Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1347-4065/acc813

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.35848/1347-4065/acb779

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Effective strategies for improving the performance of a droplet-based electricity generator (DEG) remain a challenge. Herein, we propose to introduce an intermediate layer of cyclic transparent optical polymer (CYTOP) by adjusting the thickness, injecting ionized ions into the surface, and increasing the surface area. We observed the positive effects of the introduction of a CYTOP layer on outputs, especially with a greater thickness, surface ionized-air modification and larger surface area, which could promote the practical application of DEG in energy harvesting.

DOI： 10.35848/1347-4065/acaca7

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Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/acaca7/pdf

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.tsf.2022.139597

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Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.35848/1347-4065/ac4077

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Publishing type：Research paper (scientific journal)   Publisher：{AIP} Publishing  

DOI： 10.1063/5.0083812

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acsami.1c23070

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

This study describes the fabrication of silicon nanocrystals (Si NCs) in silicon oxide layers, which led to high-performance passivation and enhanced carrier transport in crystalline silicon (c-Si) solar cells. These Si NCs comprised nanocrystalline transport pathways in ultrathin dielectrics for reinforced passivating contact structures (NAnocrystalline Trans-port path in Ultrathin dielectrics for Reinforcing (NATURE) contacts). Si NCs were formed in silicon oxide layers by depositing hydrogenated amorphous silicon oxide (a-SiOx:H) with different oxygen concentrations, followed by postdeposition annealing (PDA). Based on microscopic images, the silicon oxide layer was maintained after PDA, and the Si NCs were formed in the silicon oxide matrix, leading to a relatively low recombination current (178.8 fA/cm(2)) compared with simple a-SiOx:H layer structures. Furthermore, the contact resistivity for the NATURE contact was 13.1 m omega center dot cm(2), which was comparable to that of a single a-SiOx:H layer with a low oxygen concentration. The developed NATURE contact structure expands the design flexibility scope for various functional devices containing a passivation contact layer. It allows for the production of c-Si solar cells with passivating contacts using thicker dielectric layers for improved reliability and long-term stability.

DOI： 10.1021/acsanm.1c03355

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)  

We report on the application of Bayesian optimization (BO), which could accelerate the time-intensive process optimization of many parameters, to fabrication of the high-performance titanium oxide/silicon oxide/crystalline silicon passivating contact. The process contains pre-deposition treatment to form SiOy interlayer, atomic layer deposition (ALD) of TiOx, and hydrogen plasma treatment (HPT) as post-process. We attempted to optimize seven parameters for ALD and HPT by dealing with samples treated by three kinds of chemical solutions in the same batch. This permits to perform BO for each structure at the same time and determine the superior pre-deposition treatment. Consequently, carrier selectivity S10 estimated by independent measurements of the saturation current density and contact resistance was significantly improved by BO of only 12 cycles and 10 initial random experiments. These results certify that BO could efficiently provide experimental conditions in multidimensional parameter space although we need to consider the impact of the metallization process on the passivation performance.

DOI： 10.1016/j.solmat.2021.111251

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.35848/1347-4065/ac23ec

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/pssa.202100296

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/en14154538

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

We apply NAnocrystalline Transport path in Ultra-thin dielectrics for Reinforced passivating contact (NATURE contact) to crystalline silicon solar cells for simultaneous achievement of passivation and carrier extraction. The Si nanocrystals are formed in silicon oxide by deposition of hydrogenated amorphous silicon oxide with different oxygen concentration and subsequent annealing. NATURE contact with total layer thickness of 8 nm exhibits reasonably good passivation performance. Furthermore, we demonstrate that NATURE contact can be successfully implemented to the both sides of crystalline silicon solar cells. NATURE contact, which permits flexible structural and chemical design of a passivation contact layer, will open a possibility for various functional devices.

DOI： 10.1109/PVSC43889.2021.9519096

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Variable-angle spectroscopic ellipsometry analysis is performed to study the impact of post-deposition annealing on the passivation performance of the heterocontacts consisting of titanium oxide and silicon oxide on crystalline silicon (c-Si) prepared by atomic layer deposition (ALD) for the development of high-performance ALD-TiOx/SiOy/c-Si heterocontacts. The highest lifetime of 1.8 ms is obtained for the TiOx/SiOy/c-Si heterocontacts grown at 175 degrees C after annealing at 275 degrees C for 3 min. With increasing annealing temperature, the TiOx layers of the TiOx/SiOy/c-Si heterocontacts become dominant. Furthermore, the amplitude of dielectric functions of the ALD-TiOx layer decreases as annealing temperature increases, which suggests that enhanced diffusion of Ti into SiOy interlayers at higher annealing temperature. The sufficient diffusion of Ti atoms into SiOy interlayers is caused by annealing at 275 degrees C for 3 min, yielding high-quality interface passivation.

DOI： 10.35848/1347-4065/abd6dd

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A comparative experimental and theoretical study of the role of H incorporation in As-doped BaSi2 films has been carried out based on the experimental results that an optimal time of H treatment for the increase in photoresponsivity and carrier lifetime was in the range of 1 ? 20 min. Adequate theoretical representation of the decay curves in the framework of the model for non-radiative processes accounted for various trap-related recombination mechanisms to estimate the trap concentration to be in the range of 1.9 ? 1013 to 1.7 ? 1014 cm-3. Additionally, the extended theoretical ab initio quantum-chemical simulation of the electronic structure of the studied systems was performed. It was revealed that interstitial As atoms can mostly provide trap states in the gap while H atoms neutralize such traps. The experimentally observed unexpected switching in conductivity from n-type to p-type and vice versa in As-doped BaSi2 with H incorporation was explained to specific configurations of point defects (an As impurity with a H atom in different positions and various interatomic As-H distances) which affect the position of states in the gap.

DOI： 10.1016/j.tsf.2021.138629

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We applied hydrogen plasma treatment (HPT) on a titanium oxide/silicon oxide/crystalline silicon heterostructure to improve the passivation performance for high-efficiency silicon heterojunction solar cells. To accelerate the time-intensive process optimization of many parameters, we applied Bayesian optimization (BO). Consequently, the optimization of six process parameters of HPT was achieved by BO of only 15 cycles and 10 initial random experiments. Furthermore, the effective carrier lifetime after HPT on the optimized experimental conditions became three times higher compared with that before HPT, which certifies that BO is useful for accelerating optimization of the practical process conditions in multidimensional parameter space.

DOI： 10.35848/1882-0786/abd869

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The theoretical lateral current of the surface inversion layer in a crystalline silicon (cSi) surface for a p-aSi:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was calculated using computer simulation and was compared with the experimental one to study defects/traps at the aSi:H/cSi interface and/or in the cSi surface and to detect the acceptor concentration (N-a) in p-aSi:H. To experimentally extract the lateral surface inversion layer current, a field-effect transistor type test element group device was co-integrated with SHJ cells on the same wafer. From the correlation between the experimental and calculated lateral surface inversion layer current, the density of defects/traps (D-it) at the aSi:H/cSi interface and/or in the cSi surface and the value of N-a were extracted. The calculated lateral surface inversion layer current stayed unchanged for various minority carrier lifetimes in the substrate, suggesting that this method is not suffered from the variation in the material parameters in the substrate.

DOI： 10.35848/1347-4065/abdd02

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

The impact of hydrogen desorption on the electrical properties of TiOx on crystalline silicon (c-Si) with SiOy interlayers is studied for the development of high-performance TiOx carrier-selective contacts. Compared with the TiOx/c-Si heterocontacts, a lower surface recombination velocity of 9.6 cm/s and lower contact resistivity of 7.1 m Omega cm(2) are obtained by using SiOy interlayers formed by mixture (often called SC2). The hydrogen desorption peaks arising from silicon dihydride (alpha 1) and silicon monohydride (alpha 2) on the c-Si surface of the as deposited samples are observed. The alpha 1 peak pressure of as-deposited heterocontacts with SiOx interlayers is lower than that of heterocontacts without a SiOy interlayer. Furthermore, the hydrogen desorption energies are found to be 1.76 and 2.13 eV for the TiOx/c-Si and TiOx/SC2-SiOy/c-Si heterocontacts, respectively. Therefore, the excellent passivation of the TiOx/SC2-SiOy/c-Si heterocontacts is ascribed to the relatively high rupture energy of bonding between Si and H atoms.

DOI： 10.1016/j.cap.2020.10.002

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Publishing type：Research paper (scientific journal)  

In this paper, the Ge self-assembled islands grown at different temperatures were used as an etching mask for selective anisotropic etching of crystalline silicon (c-Si) in order to form a textured Si surface. The effects of Ge deposition temperature on the texture morphology as well as the parameters of c-Si solar cells fabricated on such structures were studied with the range of temperature from 500 °C to 800 °C. The textures on Si surface with low (<1 μm) etching margin were successfully fabricated for all investigated structures. It was revealed that usage of rapid annealing of Si wafer at 800 °C prior to epitaxial growth along with the low Ge deposition temperature of 500 °C allowed to achieve the relatively high effective carrier lifetime as compared to structures formed at higher (≥700 °C) temperatures thanks to the reduced degradation of Si wafer characteristics. Furthermore, the structure obtained using the lowest deposition temperature of 500 °C exhibited the highest light absorption among all studied samples thanks to the most homogeneous and most pyramidal texture morphology. As a result, the calculated short circuit current density JSC for the sample in which Ge islands were grown at 500 °C was as high as 35.89 mA/cm2. The proposed approach of surface texturing meets the requirements for thin c-Si solar cells due to small etching margin and the obtained results pave the way for increase the efficiency of thin c-Si solar cells by engineering the surface morphology to improve light absorption.

DOI： 10.1016/j.mssp.2020.105065

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We report on the effect of sputtering deposition of indium tin oxide (ITO) as the transparent conductive oxide layer on the passivation performance of hydrogenated amorphous silicon/crystalline silicon heterojunctions. The influence of sputtering damage on passivation performance is studied by varying the ITO layer thickness from 0 nm to 80 nm. The passivation performance decreases considerably up to 10 nm and increases gradually from 20 nm to 80 nm, indicating that damage and recovery stages are present during the sputtering process. We focus on the injection energy as the cause of the recovery phenomenon. To optimize the passivation performance by intentionally enhancing the effect of the recovery stage while minimizing the initial damage at the heterointerface, we develop a two-step sputtering process in which the radiofrequency power is changed from 50 W to 100 W during deposition to prepare ITO double layers. Two step sputtering gives the lower damage, and the properties of ITO double layers are better than those of ITO single layers. These results show that two-step sputtering can realize greater a-Si:H passivation. Furthermore, better optical properties are obtained in ITO double layers compared with conventional ITO single layers. Therefore, modulating the radiofrequency power during ITO deposition can offer higher conversion efficiency.

DOI： 10.1063/5.0009994

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Semiconducting barium disilicide (BaSi2) is an emerging material for solar cell applications, and therefore, defect passivation is critical for improving its solar cell performance. Herein, the effect of atomic hydrogen (H) on the photoresponsivity of 500 nm-thick boron (B)-doped p-BaSi2 films was examined. The photoresponsivity reached similar to 4 A/W (about twice the highest reported value for H-passivated undoped BaSi2 films) in B-doped p-BaSi2 films exposed to an atomic H supply for 5-10min because of an increased minority-carrier lifetime, as measured by the microwave-detected photoconductivity decay. Furthermore, a >= 15 min atomic H supply was found to degrade photoresponsivity. Ab initio studies were used to interpret and understand experimental observations by analyzing states in the gap region, which can act as traps, in B-doped p-BaSi2 with H incorporation. The effect that atomic H had on the performance of B-doped p-BaSi2/n-Si heterojunction solar cells was also studied. The saturation current density was found to decrease by three orders of magnitude with the atomic H supply, and the conversion efficiency was increased up to 6.2%. Deep-level transient spectroscopy revealed a reduction of defect densities induced by the atomic H supply. Both experimental and theoretical viewpoints show that an atomic H supply is beneficial for BaSi2 solar cells.

DOI： 10.1063/5.0005763

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

p-type BaSi2/n-type crystalline Si (p-BaSi2/n-Si) heterojunction solar cells with various BaSi2 thickness (d(BaSi2)) from 20 to 100 nm were fabricated using a simple preparation method, that is, post-annealing of undoped n-type BaSi2 prepared by thermal evaporation. With decreasing dBaSi(2), short-circuit current density increased due to the reduction of the parasitic absorption in p-BaSi2. On the other hand, open-circuit voltage and fill factor decreased due to the increase of the leakage current. As a consequence, the solar cell with dBaSi(2) = 80 nm showed a maximum conversion efficiency. (c) 2020 The Japan Society of Applied Physics

DOI： 10.35848/1882-0786/ab8727

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We grew 500-nm-thick lightly As-doped n-BaSi2 epitaxial films at 600 degrees C by molecular beam epitaxy, and supplied atomic H in durations (t(BaSi:H)) of 0-30 min, followed by capping with a 3-nm-thick amorphous Si layer at 180 degrees C. The photoresponsivity of the BaSi2 films was enhanced by approximately five times by As doping. Deep-level transient spectroscopy measurement revealed the disappearance of two previously reported electron traps. The photoresponsivity was further enhanced by approximately six times after H supply. It reached a maximum at t(BaSi:H) = 1-10 min, owing to the reduction of defects.

DOI： 10.35848/1882-0786/ab8725

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The lateral transport of minority carriers in the surface inversion layer of a crystalline silicon (cSi) surface for a p-aSt:H/i-aSi:H/cSi heterojunction (SHJ) solar cell was experimentally analyzed to study defects/traps at the aSi:H/cSi interface and/or on the cSi surface. To extract the lateral surface inversion layer current, a field-effect transistor type test element group device was designed and fabricated on a cSi wafer where SHJ cells were co-integrated. By analyzing the lateral surface inversion layer current, the effective surface minority carrier mobility was calculated. The extracted mobility was one order of magnitude smaller than that of a reference MoOx/i-aSi:H/cSi structure but it increased by low-temperature post-deposition annealing with respect to the reference, This method is highly sensitive to the quality of the aSi:H/cSi interface and/or the cSi surface, The density of trap sites was estimated to be of the order of 10(11) cm(-2) at the aSi:H/cSi interface and/or an the cSi surface. (C) 2020 The Japan Society of Applied physics

DOI： 10.35848/1347-4065/ab70a0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the synthesis of Mg2Si thin films from a Mg-Si solution by thermal treatment of Mg on a Si substrate under an Ar gas atmosphere. The Mg was prepared by two methods. One is to deposit Mg films by thermal evaporation, and another is to simply place Mg ribbons on Si. After thermal treatment, a two-layer structure consisting of oxide and similar to 1 mu m-thick Mg2Si films with {100} preferential orientation was observed for the sample prepared by thermal evaporation. On the other hand, similar to 10 mu m-thick single layer Mg2Si with more random orientations and cracks was formed for the Mg ribbon contact samples. Possible mechanisms for different structures, crystal orientations, and crack formation are discussed. (c) 2020 The Japan Society of Applied Physics

DOI： 10.35848/1347-4065/ab6b79

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Publishing type：Research paper (international conference proceedings)  

We formed carbon (C)-doped BaSi2 films by RF sputtering of BaSi2 and SiC targets simultaneously, and measured their optical properties. In the Raman spectra of BaSi2 films, peaks corresponding to vibrational modes of Si tetrahedra in the lattice of BaSi2 appear. On the other hand, in C-doped BaSi2 films, new peaks at around 260, 310, and 630 cm-1 other than those of BaSi2 films were observed. As the RF power of the SiC target (P SiC) increased, these intensities increased. The absorption edge of C-doped BaSi2 films was shifted to higher energies from 1.19 to 1.30 eV with increasing P SiC. We achieved the highest photoresponsivity of 1 A W-1 ever achieved for BaSi2 films at a bias voltage of 0.1 V applied between the top and bottom electrodes. The marked enhancement of photoresponsivity was interpreted to originate from the increased carrier lifetime in C-doped BaSi2 films.

DOI： 10.35848/1347-4065/ab69dc

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The effects of vapor composition during evaporation and post-annealing conditions on the carrier density of undoped BaSi2 films were investigated. Regardless of the vapor composition during evaporation, the carrier density after post-annealing changed in the range between 10(16) and 10(17) cm(-3) by changing the post-annealing temperature. In addition, post-annealing above 920 degrees C induced carrier type transition from n-type to ptype. The temperature at which the carrier type transition occurred was found to depend on the surface covering material during post-annealing, which implies that the carrier type transition could originate from the change of the BaSi2 film composition to Si-rich. (c) 2020 The Japan Society of Applied Physics

DOI： 10.7567/1347-4065/ab6418

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：A V S AMER INST PHYSICS  

The authors report on the effect of hydrogen plasma treatment (HPT) on the passivation performance of titanium oxide (TiOx) on crystalline silicon (c-Si) fabricated by atomic layer deposition. Recently, TiOx has gathered attention as an electron-selective contact material for silicon heterojunction (SHJ) solar cells due to its preferable work function and band lineup. Moreover, TiOx has excellent light transmission properties due to its large bandgap energy. In order to improve the power conversion efficiency of SHJ solar cells with TiOx, it is necessary to enhance the passivation performance. The effective carrier lifetime representing the passivation performance is enhanced by HPT and amounts to 407.2 mu s after HPT at 200 degrees C for 1min. This value is twice as high as after forming gas annealing, which is the standard method to enhance the passivation performance of TiOx/c-Si heterostructures. Nuclear reaction analysis clarifies that the hydrogen concentration (C-H) at the TiOx/c-Si interface of the HPT-processed sample is higher than that of an as-deposited sample and that the peak position of the C-H distribution is shifted closer to the TiOx/c-Si heterointerface after HPT. Moreover, thermal desorption spectroscopy shows that Si-H and Si-H-2 hydrogen bonds increase with HPT. These results indicate that the atomic hydrogen produced by the hydrogen plasma diffuses toward the TiOx/c-Si interface and terminate the local dangling bonds, which is responsible for the improved passivation performance.

DOI： 10.1116/1.5134720

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：A V S AMER INST PHYSICS  

Crystalline silicon (c-Si) heterojunction solar cells using carrier-selective contacts have drawn considerable attention due to their high power conversion efficiency with a simple fabrication process. Titanium oxide (TiOx) is one of the most promising materials that can provide excellent surface passivation as well as carrier-selective transport. In this study, the authors fabricate the TiOx/SiOx/c-Si heterocontacts by atomic layer deposition (ALD) and investigate the effect of the forming gas annealing (FGA) on hydrogen content and surface morphology by utilizing nuclear reaction analysis (NRA) and atomic force microscope (AFM) measurements, respectively. The highest effective carrier lifetime (tau(eff)) of 891 mu s is realized for TiOx/SiOx/c-Si heterocontacts after FGA at 400 degrees C for 3 min, indicating that high surface passivation performance is obtained. NRA clarifies that the hydrogen content in the TiOx/SiOx/c-Si heterocontacts decreases with increasing FGA temperature and duration. With increasing FGA temperature and duration, also the surfaces of the TiOx/SiOx/c-Si heterocontacts are roughened, which means enhanced crystallization of the TiOx/SiOx/c-Si heterocontacts. From the NRA and AFM analyses, the authors conclude that there is a trade-off relationship between the hydrogen content in the TiOx/SiOx/c-Si heterocontacts and the crystallization of the TiOx layers.

DOI： 10.1116/1.5134719

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGEROPEN  

Silicon quantum dot (Si-QD) embedded in amorphous silicon oxide is used for p-i-n solar cell on quartz substrate as a photogeneration layer. To suppress diffusion of phosphorus from an n-type layer to a Si-QD photogeneration layer, niobium-doped titanium oxide (TiOx:Nb) is adopted. Hydrofluoric acid treatment is carried out for a part of the samples to remove the thermal oxide layer in the interface of TiOx:Nb/n-type layer. The thermal oxide acts as a photo-generated carrier-blocking layer. Solar cell properties using 10-nm-thick TiOx:Nb without the thermal oxide are better than those with the thermal oxide, notably short circuit current density is improved up to 1.89 mA/cm(2). The photo-generated carrier occurs in Si-QD with quantum confinement effect. The 10-nm-thick TiOx:Nb with the thermal oxide layer effectively blocks P; however, P-diffusion is not completely suppressed by the 10-nm-thick TiOx:Nb without the thermal oxide. These results indicate that the total thickness of TiOx:Nb and thermal oxide layer influence the P-blocking effect. To achieve the further improvement of Si-QD solar cell, over 10-nm-thick TiOx:Nb is needed.

DOI： 10.1186/s11671-020-3272-8

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We apply silicon nanocrystals as a carrier transport route in silicon oxide for polycrystalline silicon on oxide (POLO) junctions. The Si nanocrystals are formed in silicon oxide by deposition of hydrogenated amorphous silicon oxide with different oxygen concentration and subsequent annealing. From cross-sectional transmission electron microscopy (TEM) images, the Si nanocrystals are observed for the sample at annealing temperature of 750 degrees C. The highest average effective lifetime of about 630 mu s and contact resistivity of 25.5 m Omega.cm are obtained before hydrogenation process.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We investigate an influence of thermal treatment on the properties of tin-doped indium oxide (ITO) and In2O3 on glass and hydrogenated amorphous silicon (a-Si:H)/glass. Work function (WF), electron density and mobility of the In2O3 are dependent on a-Si:H underlayer possibly due to H diffusion from -Si:H underlayer by annealing. In addition, WF of the In2O3 is higher than that of the ITO regardless of presence of a-Si:H underlayer. Furthermore, the ITO/In2O3 double layers are fabricated for silicon heterojunction (SHJ) solar cells. The electrical and optical properties of the ITO/In2O3 stacks are adequate for transparent conductive oxide (TCO) layer.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Carrier-selective contacts prepared by atomic layer deposition (ALD) have received significant attention for developing high-efficiency solar cells. Herein, the electrical properties of titanium oxide (TiOx) prepared by ALD are manipulated by modulating the deposition temperature during ALD. Tunable electrical properties are possible due to the existence of oxygen vacancies in TiOx prepared at low deposition temperatures. TiOx layers prepared at 100 and 150 degrees C provide a low contact resistivity and high passivation performance, respectively. A high carrier selectivity of 13.5 is achieved by stacking the TiOx layers prepared at 100 and 150 degrees C, compared with a single TiOx layer. Modulating the deposition temperature can, therefore, improve the electrical properties of ALD-TiOx. This approach can be used to optimize the functionality of ALD-based materials.

DOI： 10.1002/pssa.201900495

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We studied the effect of deposition temperature on the hydrogen distribution and the passivation performance of hydrogenated amorphous silicon (a-Si:H) coated crystalline silicon (c-Si) heterojunctions as a model of high efficiency solar cell structures. Nuclear reaction analysis (NRA) was employed to obtain hydrogen depth profiles of the heterojunctions prepared at temperatures from 80 to 180 degrees C. The implied open circuit voltage (i-V-OC) and carrier lifetime monotonically increased with increasing deposition temperature in the as-deposited samples. NRA clarified that the hydrogen concentration (C-H) at the a-Si:H/c-Si interface and in the a-Si:H layer decreased with deposition temperature. The hydrogen concentration around the interface was roughly 3 x 10(21) cm(-3) for the sample deposited at 180 degrees C. The NRA results are supplemented by optical constants obtained with spectroscopic ellipsometry (SE). At higher growth temperature, larger refractive indices and extinction coefficients were confirmed by SE analysis, suggesting that fewer hydrogen atoms are incorporated into the a-Si:H layers prepared at higher growth temperature. Furthermore, the passivation performance was enhanced by post deposition annealing (PDA) at 200 degrees C for 30 min. No significant change of the hydrogen distribution and optical constants was observed after PDA, suggesting that improved passivation is due to a local rearrangement of hydrogen at the molecular level that results in enhanced hydrogenation of dangling bonds.

DOI： 10.1063/1.5100086

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A new aspect of solute PEDOT:PSS was explored, its function as an excellent passivation material. Solute PEDOT:PSS with a thickness of 9.4 nm exhibited an effective carrier lifetime of 940 mu s at an injection level of 1 x 10(14) cm(-3). A new architecture of hybrid crystalline silicon solar cells with highly conductive PEDOT:PSS on the front side and solute PEDOT:PSS on the backside was demonstrated. The reverse saturation current density Jo of 9.4 nm-thick solute PEDOT:PSS was evaluated as 2.2 x 10(-14) A cm(-2), which is ten times lower than that without solute PEDOT:PSS on the backside, 1.45 x 10(-13) A cm(-2). With the introduction of 7.5 nm-thick solute PEDOT:PSS on the backside, the performance drastically improved with an open-circuit voltage V-OC of 618 mV, short-circuit current density J(SC) of 28.33 mA cm(-2) and power conversion efficiency E-ff of 11.45% owing to efficient passivation. Employment of solute PEDOT:PSS as an efficient passivation material opens a new route for the fabrication of hybrid c-Si solar cells, which is facile, reproducible and environmentally friendly.

DOI： 10.1039/c9se00093c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Passivation of barium disilicide (BaSi2) films is very important for their use in solar cell applications. In this paper, we demonstrated the effect of hydrogen (H) passivation on both the photoresponsivity and minority-carrier lifetime of BaSi2 epitaxial films grown by molecular beam epitaxy. First, we examined the growth conditions of a 3-nm-thick hydrogenated amorphous silicon (a-Si) capping layer formed on a 500-nm-thick BaSi2 film and found that an H supply duration (ta-Si:H) of 15 min at a substrate temperature of 180 degrees C sizably enhanced the photoresponsivity of the BaSi2 film. We next supplied atomic H to BaSi2 epitaxial films at 580 degrees C and changed supply duration (t(BaSi;H)) in the range of 1-30 min, followed by capping with an a-Si layer. The photoresponsivity of the films changed considerably depending on t(BaSi;H )and reached a maximum of 2.5 A/W at a wavelength of 800 nm for the sample passivated for t(BaSi;H )= 15 min under a bias voltage of 0.3 V applied to the front-surface indium-tin-oxide electrode with respect to the back-surface aluminum electrode. This photoresponsivity is approximately one order of magnitude higher than the highest value previously reported for BaSi2. Microwave photoconductivity decay measurements revealed that the minority-carrier lifetime of the BaSi2 film with the highest photoresponsivity was 14 mu s, equivalent to its bulk carrier lifetime ever reported. We performed theoretical analyses based on a rate equation including several recombination mechanisms and reproduced the experimentally obtained decay curves. We also calculated the total density of states of BaSi2 by ab initio studies when one Si vacancy existed in a unit cell and one, two, and three H atoms occupied Si vacancy or interstitial sites. A Si vacancy caused a localized state with two energy bands to appear close to the middle of the band gap. In certain cases, H passivation of the Si dangling bonds can markedly decrease trap concentration. From both experimental and theoretical viewpoints, we conclude that an atomic H supply is beneficial for BaSi2 solar cells.

DOI： 10.1103/PhysRevMaterials.3.065403

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on a simple liquid-phase epitaxy (LPE) of SiGe on Si (100) substrate based on printing and firing. LPE was performed using an Al-Ge mixed paste screen-printed on a Si (100) substrate followed by annealing above the Al-Ge eutectic temperature in air or in an Ar atmosphere. In the case of annealing in air at 800 degrees C, SiGe was formed between the mixed paste and the surface of the Si substrate. However, a wave-like oxide film was confirmed at the SiGe/Si interface, which hindered the growth of SiGe. On the other hand, annealing in the Ar atmosphere at 800 degrees C led to the successful formation of a more continuous, thicker SiGe film by suppressing the oxidation of Al. It can be concluded that LPE growth using printing and firing of Al-Ge mixed paste is a suitable method to grow SiGe with a low-cost and simple high-speed process. (C) 2019 The Japan Society of Applied Physics

DOI： 10.7567/1347-4065/ab00e5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The impact of the size distributions of Ge islands on the structural and optical characteristics of anti-reflection structures was investigated. The variation of island size distribution was achieved through the variation of growth temperature in gas-source molecular beam epitaxy at 700 degrees C-800 degrees C. Ge islands were utilized as etching masks to form the anti-reflection structures. By using lower growth temperature of 700 degrees C and subsequent etching, larger texture without many hollows was formed in contrast to that using 800 degrees C. Broader size distribution of islands formed at 700 degrees C was found to lead to larger texture size. Smaller texture is formed by smaller islands and short etching, whereas larger texture is formed by erosion of smaller texture during long etching. A potential short-circuit current density of 36.75 mA cm(-2) was obtained for the sample by the islands grown at 700 degrees C with reduced etching margins, comparable to that of conventional pyramid textures. (C) 2019 The Japan Society of Applied Physics

DOI： 10.7567/1347-4065/ab003b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Silicon nanowires (SiNWs) show a great potential for energy applications because of the optical confinement effect, which enables the fabrication of highly efficient and thin crystalline silicon (c-Si) solar cells. Since a 10-m-long SiNW array can absorb sufficient solar light less than 1200nm, the 10-m-long SiNW was fabricated on Si wafer to eliminate the influence of the Si wafer. On the other hand, Surface passivation of the SiNWs is a crucial problem that needs to be solved to reduce surface recombination and enable the application of SiNWs to c-Si solar cells. In this study, aluminum oxide (Al2O3) was fabricated by atomic layer deposition for the passivation of dangling bonds. However, owing to a complete covering of the SiNWs with Al2O3, the carriers could not move to the external circuit. Therefore, chemical-mechanical polishing was performed to uniformly remove the oxide from the top of the SiNWs. A heterojunction solar cell with an efficiency of 1.6% was successfully fabricated using amorphous silicon (a-Si). The internal quantum efficiencies (IQE) of the SiNW and c-Si solar cells were discussed. In the wavelength region below 340nm, the IQE of the SiNW solar cell is higher than that of the c-Si device, which results in an increase of the absorption of the SiNW cells, suggesting that SiNWs are promising for crystalline-silicon thinning.

DOI： 10.1186/s11671-019-2930-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

This study proposes metal-assisted chemical etching (MAE) as a facile method to fabricate silicon nanowire (SiNW) array structures, with high optical confinement for thin crystalline silicon solar cells. Conventional SiNW arrays are generally fabricated on Si wafer substrates. However, tests on conventional SiNW-based solar cells cannot determine whether the photo-current is derived from SiNWs or from the Si wafer. Herein, SiNW arrays were fabricated on a silicon-on-insulator substrate with a 10-mu m-thick silicon layer for measuring the photo-current of the SiNW only. The 9 mu m-long p-type SiNW arrays were applied to a solar cell structure fabricated using an n-type H-doped amorphous Si layer, thereby confirming the photovoltaic effect. However, the device exhibited a conversion efficiency of 0.0017% because of a low short-circuit current (J(sc)) and a low open-circuit voltage (V-oc). The low J(sc) resulted from a high series resistance and high absorption loss from the amorphous Si layer, whereas the low V-oc resulted from the high surface recombination velocity of the SiNW array structure. Therefore, reducing the surface recombination of SiNW-based solar cells can improve their conversion efficiency.

DOI： 10.3390/app9050818

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Recent increases in the power conversion efficiency of crystalline silicon (c-Si) heterojunction (SHJ) solar cells are due to implementation of carrier-selective contacts (CSCs) with high passivation performance and low contact resistivity. These electrical properties of CSCs significantly depend on the nature of the CSCs/c-Si interface at the atomistic scale, and precise control of the interface with the SiOx interlayer is the key to obtaining superior electrical properties. It is shown that a TiOx/c-Si structure with an interlayer prepared by nitric acid at room temperature shows the best performance among points with five different interlayer formation methods. The underlying mechanisms are investigated by combining high-resolution transmission electron microscopy and electron energy loss (EEL) spectroscopy. The EEL spectra reveal that the Si:O ratio of an as-deposited SiOx interlayer is nonstoichiometric (x < 2), which could contribute to lower contact resistivity. Furthermore, the as-deposited SiOx leads to formation of a Ti containing SiOx layer with few oxygen vacancies after forming gas annealing, resulting in the significant enhancement of passivation performance. These results show that the control of the interlayer with atomistic scale is of crucial importance to realize higher power conversion efficiency of SHJ solar cells.

DOI： 10.1002/admi.201801645

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Passivation of BaSi2 film is very important for their use in solar cell applications. In this paper, we demonstrated the effect of hydrogen (H) passivation on both the photoresponsivity and minority-carrier lifetime of BaSi2 epitaxial films grown by molecular beam epitaxy. We supplied atomic H to BaSi2 epitaxial films at 580 degrees C and changed supply duration (t(H)) in the range of 0-30 min, followed by capping with an amorphous Si (a-Si) layer. The photoresponsivity of films changed considerably depending on t(H) and reached a maximum of 2.5 A/W at a wavelength of 800 nm for the sample passivated for t(H) = 15 min under the bias voltage of 0.3 V applied to the front-surface indium-tin-oxide electrode with respect to the back-surface aluminum electrode. This photoresponsivity is approximately one order of magnitude higher than the highest value previously reported for BaSi2 . Furthermore, microwave photoconductivity decay measurements revealed that the minority-carrier lifetime of the BaSi2 film with the highest photoresponsivity was 14 mu s, equivalent to its bulk carrier lifetime ever reported.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the activation mechanism of titanium oxide (TiOx) prepared by atomic layer deposition on crystalline silicon (c-Si), which is regarded as a prominent electron-selective contact with ideal band alignment and low carrier recombination for Si heterojunction solar cells. The activation energy of surface passivation was revealed to be about 0.37 eV, which was shown to be associated with the marked transformation of the chemical bonding states at the TiOx/c-Si interface. Detailed analysis confirmed that Si-O bonds are formed after postannealing, owing to the dissociation of the Si-H and Si-H-2 bonds at the interface and subsequent termination by oxygen atoms. (C) 2018 The Japan Society of Applied Physics

DOI： 10.7567/APEX.11.102301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on our attempt to increase the carrier density in the p-type polycrystalline silicon (poly-Si) layers grown by aluminum-induced crystallization (AIC) employing a B-doped Si target. Hall measurement revealed that we could obtain a lower-resistance and heavily doped p-type continuous poly-Si thin layer formed by AIC using B-doped a-Si. According to our evaluation of tunnel oxide passivated contact (TOPCon) solar cells with AIC-grown poly-Si, the AIC-TOPCon solar cells fabricated at 570 degrees C using B-doped a-Si showed higher conversion efficiency of 13.5% than that of 12.8% when using nondoped a-Si. It is considered that the cell characteristics, particularly FF and V-oc, were improved owing to the lower series resistance and higher carrier density since both Al and B were successfully incorporated into the AIC-grown poly-Si. (C) 2018 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.57.08RB12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

A light-trapping structure was fabricated on crystalline Si wafers. In this method, a Ge/Si(001) self-assembled dot structure was etched using KOH and a commercial alkaline solution including nanomask particles. Many nanoscale islands were formed by adding the nanomask particles. The enhancement of light absorption was successfully confirmed in samples with nanostructures after etching. Since the etching margin of a nanostructure was less than 2 mu m, the nanostructure could be applied to an ultrathin Si substrate. To investigate the effect of surface passivation on the nanostructure, the nanostructure was passivated using hydrogenated amorphous Si thin films by plasma-enhanced chemical vapor deposition. By quasi-steady-state photoconductance measurement, the suitable implied open-circuit voltage and implied fill factor for heterojunction solar cells were obtained. From calculations based on these parameters, solar cells with nanostructures at a substrate thickness of 100 mu m are expected to have a conversion efficiency of 23.21%. (C) 2018 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.57.08RF09

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Electrical and structural properties of TiO2 thin films deposited at room temperature by reactive DC sputtering have been investigated on three different substrates: high resistivity (>1000 Omega cm) float zone Si(1 1 1), float zone Si(1 00) and alkali free glass. As-deposited TiO2 films on glass substrate showed extremely high resistivity of (similar to 5.5 x 10(3) Omega cm). In contrast, lower resistivities of similar to 2 Omega cm and similar to 5 Omega cm were obtained for films on Si(1 1 1) and Si(1 0 0), respectively. The as-deposited films were found to be oxygen-rich amorphous TiO2 for all the substrates as evidenced by X-ray photoemission spectroscopy and X-ray diffraction. Subsequent annealing led to appearance of anatase TiO2 on Si but not on glass. The surface of as-deposited TiO2 on Si was found to be rougher than that on glass. These results suggest that the big difference of electrical resistivity of TiO2 would be related with existence of more anatase nuclei forming on crystalline substrates, which is consistent with the theory of charged clusters that smaller clusters tend to adopt the substrate structure. (C) 2018 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2018.04.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We studied the surface passivation effect of hydrogenated amorphous silicon (a-Si:H) layers on BaSi2 films. a-Si: H was formed by an electron-beam evaporation of Si, and a supply of atomic hydrogen using radio-frequency plasma. Surface passivation effect was first investigated on a conventional n-Si(111) substrate by capping with 20 nm-thick a-Si: H layers, and next on a 0.5 mu m-thick BaSi2 film on Si(111) by molecular beam epitaxy. The internal quantum efficiency distinctly increased by 4 times in a wide wavelength range for sample capped in situ with a 3 nm-thick a-Si: H layer compared to those capped with a pure a-Si layer. (C) 2018 Author(s).

DOI： 10.1063/1.5025021

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

RF magnetron sputtered Nb doped titanium oxide (TiO2:Nb) thin film on alkali-free glass substrate is shown to provide good transparency and low resistivity. Both the optical and electrical properties are closely dependent on the deposition parameters as well as the post-annealing process. The impact of deposition power (100-400 W), deposition temperature (25-200 degrees C) and O-2/O-2+Ar flow rate ratio (0-9.09%) on the optical and electrical properties have been studied. A significant improvement of the conductivity of TiO2:Nb thin film is observed after annealing at 600 degrees C over 60min, leading to the decrease of resistivity from 7x10(3) Omega.cm to 2x10(-3) Omega.cm and the transparency over 70% in the visible wavelength. Due to its high work function and the obtained good opto-electrical property, TiO2:Nb has a great potential as an electron selective contact for dopant-free Si solar cells or transparent conductive oxide material.

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.24752/gre.1.0_46

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

To obtain silicon quantum dot (Si-QD) multilayers, amorphous silicon oxide (a-SiOx) films have been prepared by plasma enhanced chemical vapor deposition (PECVD) using SiH4 and CO2. As increasing CO2 flow rate, crystal volume of Si was decreased and optical gap was increased. This results suggest the increasing of oxygen content in samples. From this analysis, Si-QD multilayers having different Si-QD size were fabricated and were evaluated for structural properties. A cross-sectional transmission electron microscopy image showed the formation of Si-QDs with the diameter of about 5 nm. PL spectra showed the bandgap was blue-shifted to 1.3 eV with decreasing the size of Si-QDs to 5 nm, indicating the quantum size effect appeared in these samples.

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We investigated the local structure at the interface between titanium oxide (TiOx) and crystalline Si (c-Si) with silicon oxide (SiOx) interlayers by employing the electron energy loss (EEL) spectroscopy to clarify the origin of the high performance TiOx passivating layer deposited by atomic layer deposition. Five kinds of TiOx/SiOx/c-Si structures were fabricated and the best passivation performance was achieved by the SiOx interlayer formed by nitric acid at room temperature. EEL spectra revealed that Ti-contained more stoichiometric SiOx including few oxygen vacancies and Ti-O-Si bonding would be formed after forming gas annealing, resulting in the enhancement of passivation performance.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

An intrinsic silicon nanoparticle (i-SiNP) layer was fabricated using the spin-coating technique and utilized as the active layer of a solar cell. The electrical conductivity of the i-SiNP layer was enhanced via press treatment, which increased the density and electrical conductivity of the SiNPs. Raman spectroscopy and electron-spin resonance results indicated that the SiNPs were only in contact with each other and were not bound together. To fabricate a solar cell with an i-SiNP active layer, a-Si was used to synthesize the p- and n-type doping layers. The open-circuit voltage of the cell was 140mV.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The surface passivation effect of hydrogenated amorphous silicon (a-Si:H) layers on BaSi2 film was studied. a-Si: H layers were formed by electron-beam evaporation of Si and subsequent or simultaneous supply of atomic hydrogen using a radio-frequency (RF) plasma generator. The hydrogen concentration in a-Si: H layers was measured by secondary ion mass spectrometry to be in the range of 10(21) cm(-3). The Si-H and Si-H-2 bonds were confirmed by Raman spectroscopy. Next, we applied a-Si:H layers on a medium-doped n-Si(111) substrate (resistivity rho = 6-9 Omega cm), the passivation properties were verified by quasi-steady-state photoconductivity measurement. Finally, the photoresponsivity of 500-nm-thick BaSi2 film capped with 3-nm-thick a-Si:H layers was improved by a factor of 4 compared to those capped with the pure amorphous Si (a-Si).

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Heterojunction solar cells were fabricated with novel light trapping structure formed by selective etching using Ge dots as an etching mask. The light trapping structure has a lot of islands with submicron scale and nanoscale. Etching margin was less than 2 mu m. The light trapping structure was fabricated by changing the parameter of the Ge layer. As a result, the sample fabricated at the Ge coverage of 60 monolayers (MLs) had the largest island structure. The solar cell with the structure with Ge coverage of 60MLs showed high short-circuit current density of 39.7 mA/cm(2). This is because the novel light trapping structure consisted of submicron textures and nanoscale textures and enhanced the light absorption in a wide range.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The passivation of the heterojunction interfaces between the carrier selective contact and the crystalline silicon (cSi) is crucial to achieve high power conversion efficiency in the silicon heterojunction solar cells. We develop a passivation layer applicable to the hole selective contact copper iodide (Cul) fabricated by the 2-step method which includes direct deposition of copper (Cu) on the substrate. The intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer and the intrinsic hydrogenated amorphous silicon oxide (i-a-SiOx:II) layer are stacked on c-Si substrate by the plasma enhanced chemical vapor deposition (PECVD) before Cul fabrication. We demonstrate that the i-aSiO(x):H layer prevents Cu from diffusing into the i-a-Si:H layer and degrading the minority carrier lifetime of the substrate.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

BaSi2 films were fabricated on textured Si(001) substrates that consisted of {111} facets using molecular beam epitaxy. The light-trapping effect of these films and their performance when incorporated into solar cells were measured. X-ray diffraction and reflectivity measurements showed that the BaSi2 films were grown epitaxially on the textured Si(001) substrate and confirmed the light-trapping effect. The critical thickness over which BaSi2 relaxes increased from approximately 50 to 100 nm when comparing the BaSi2 films on a flat Si(111) substrate and the textured substrate, respectively. p-BaSi2/n-Si solar cells were fabricated with varying BaSi2 layer thickness and with hole concentrations in the range between 2.0 x 10(18) and 4.6 x 10(18) cm (3). These cells exhibited a maximum energy conversion efficiency of 4.62% with an open-circuit voltage of 0.30 V and a short-circuit current density of 27.6 mA/cm(2) when the p-BaSi2 layer was 75 nm-thick. These results indicated that the use of BaSi2 films on textured Si (001) substrates in solar cells shows great promise. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2017.06.017

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We applied aluminum-induced crystallization (AIC) as a technique to realize heavily doped p-type polycrystalline Si layer at low temperature for the rear side of tunnel oxide passivated contact concept solar cell. Systematic temperature variation of AIC revealed that annealing at a temperature slightly lower than the eutectic temperature (577 degrees C) is effective to improve solar cell performance. This is explained by reduced resistivity for low contact resistance while avoiding melting of Al-Si.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We report on structural and optical properties of copper iodide (CuI) on crystalline Si (c-Si) and properties of the diode with intrinsic type (i-type) hydrogenated amorphous Si (aSi: H) at CuI/c-Si interface. The i-type a-Si: H layer was deposited on n-type c-Si by catalytic chemical vapor deposition (Cat-CVD) prior to deposition of CuI by spin-coating method. Higher rotational speed of 4000 rpm was found to be useful to suppress generation of large particles and absorption by CuI. The effective carrier lifetime was characterized for CuI/a-Si: H/c-Si/a-Si: H/CuI structures and it strongly depended on a-Si: H. The CuI/a-Si: H/cSi diodes showed rectification behavior.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

We studied on surface morphology, optical properties and passivation performance of copper iodide (CuI) on crystalline silicon (c-Si) deposited by spin-coating for application to hole-selective contacts to realize high performance and low-cost c-Si solar cells. Absorbance was increased by depositing CuI on c-Si owing to absorption and antireflection effect of Cut From surface images by scanning electron microscope measurements, discontinuous layer was observed for CuI deposited Si. Effective lifetime was characterized for c-Si with ultra-thin oxide covered by CuI both sides by using a microwave photoconductive decay. The lifetime increased from 2 mu s to order of 10 mu s by introducing CuI layer possibly due to large conduction band offset. (C) 2017 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2017.09.081

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

We fabricated 20-layer-stacked Ge/Si1-xCx quantum dots (QDs) by solid source molecular beam epitaxy, for the realization of Si-based, strain-compensated Ge QDs. We inserted 2-nm-thick Si mediating layers between the Ge QDs and the Si1-xCx strain-compensating spacer layers (SCLs) and evaluated their influence on the structural and optical properties of the obtained system. High density QDs with a size fluctuation of approximately 14% were successfully maintained independent of the number of stacked layers in the case of QDs with Si mediating layers, while the QD size monotonically increased with a number of stacked layers in the case of QDs without Si mediating layers. The sheet density of QDs with Si mediating layers reached 1.2 x 10(11) cm(-2). A strong photoluminescence (PL) emission with a line-width of 96.7 meV was obtained for the QDs with Si mediating layers. The improvement of the aforementioned properties was caused by both the absence of C bonds at the surface and the improved surface roughness obtained by introducing Si mediating layers. The QD size increased for the 20-layer-stacked Ge/Si QDs samples grown with 10-nm-thick spacer layers, due to the accumulation of internal strains. By contrast, the size distribution of QDs was almost constant for the range of spacer layer thicknesses used in the present work (between 10 am and 40 nm), implying that the tensile-strained Si1-xCx SCLs compensated a certain fraction of the strain field created by the compressive-strained Ge QDs. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2015.02.043

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

We have studied the effect of the deposition rate on the structural and optical characteristics of five-layer-stacked Ge self-assembled quantum dots (QDs) on a Si (001) substrate grown by molecular beam epitaxy. Ge QDs were formed using a pulse growth technique, which consists of high-rate Ge deposition and an interruption in growth. In this work, the deposition rate was varied from 1.1 angstrom/s to 2.8 angstrom/s. Pyramid-shaped QDs with a monomodal size distribution were obtained at 2.8 angstrom/s, while a bimodal size distribution including pyramid-shaped QDs and multifaceted dome-shaped QDs was observed between 1.1 angstrom/s and 2.2 angstrom/s. As a result, an improved size fluctuation of 11.1% and highest sheet density of 5.6 x 10(10) cm(-2) were achieved for the QD sample grown at 2.8 angstrom/s. As for the optical characteristics, a single photoluminescence (PL) emission line at 0.825eV with a width of 86.1 meV was observed at 12K. Furthermore, we found that the PL emission from the Ge QDs shows type-II emission characteristics, i.e., the shift of the PL peak energy with respect to the PL excitation power (P-exc) was proportional to P-exc(1/3). (c) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2013.10.071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have studied Ge self-assembled quantum dots (QDs) grown by molecular beam epitaxy on Si (001) substrates. We investigated the effect of a pulse growth technique, which involves the combination of a high deposition rate of 2.8 angstrom/s and a 5-s growth interruption (GI) time, on the properties of 20-layer stacked Ge QDs. We found that both the size and size dispersion of the QDs grown using the pulse growth technique were successfully maintained without generating any dislocations even after 20 layers of stacking. Further, a high sheet density of 6.9 x 10(10) cm(-2) and better size dispersion of 12.4% can be achieved. In photoluminescence (PL) measurements, PL emission at 0.833 eV with line width of 71.2 meV was clearly observed at 12 K for 20-layer stacked Ge QDs grown using the pulse growth technique. (c) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2012.12.121

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Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2020.9

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Event date： 2020.9

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Event date： 2020.9

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Event date： 2020.9

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Event date： 2020.9

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Event date： 2020.6

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