Shunsuke Kasashima

Effect of light intensity on performance of silicon-based thin film solar cells

Theoretical and experimental studies were performed to explore the effect of light intensity on the performance of silicon-based thin film solar cells. The theoretical study was conducted using AMPS-1D (Analysis of Microelectronic and Photonic Structures) to analyze how the device structure affects the performance of silicon-based solar cells under various concentration ratios of sunlight. We calculated a-Si:H and μc-Si:H p-i-n type single-junction solar cells, and also experimentally evaluated a-Si:H, a-SiO:H and μc-Si:H solar cells. From both simulation and measurement results, we confirmed that the Voc logarithmically increases with increasing the light intensity. Moreover, from simulation results, we also observed that the defect density and thickness of i-layer strongly influence the light-intensity dependence of a-Si:H solar cells.

Performance of multi-junction silicon-based thin film solar cells under concentrated sunlight

Multi-junction silicon-based thin-film concentrator solar cells are promising candidate to achieve both low-cost and high-efficiency. For the application of silicon-based thin film solar cells to concentrator photovoltaics, it is required to be revealed the light intensity dependence of the performance of silicon-based thin film solar cells. From these reasons, in this study both calculation and experimental studies were conducted with several types of single-junction and multi-junction tandem solar cells. From both simulation and measurement results, we observed that double- and triple-junction solar cells achieve high open-circuit voltage and large logarithmic increment in open-circuit voltage with increasing light intensities. On the other hand, it became clear that the drop of fill factor is required to be improved for the realization of the multi-junction silicon-based thin-film solar cells with very high efficiency under low concentration ratios of sunlight.

Amorphous silicon solar cells with novel mesh substrates for concentrator photovoltaic applications

To develop multi-junction thin-film silicon concentrator photovoltaics, we have introduced a novel mesh substrate with low sheet resistance (SANTE− substrate, developed by Cima NanoTech). In this study, we fabricated a-Si:H single junction solar cells on SANTE− substrate and successfully improved Voc and F.F. of a-Si:H solar cells on SANTE− substrate with buffer layer at TCO/p interface. We have studied the light intensity dependence of PV parameters of with various i-layer thicknesses and have shown improvement of F.F. and Eff. by the effects of both low sheet resistance TCO and reducing i-layer thickness.

Hetero-junction microcrystalline silicon solar cells with wide-gap p-μc-Si 1−x O x :H layer

Preparation of p-type hydrogenated microcrystalline silicon oxide thin films (p-μc-Si<inf>1−x</inf>O<inf>x</inf>:H) by 13.56 MHz RF-PECVD method for use as a p-layer of hetero-junction μc-Si:H solar cells is presented. We investigated effects of wide-gap p-μc-Si<inf>1−x</inf>O<inf>x</inf>:H layer on the performance of hetero-junction μc-Si:H solar cells under various light intensity. We observed that a wide-gap p-μc-Si<inf>1−x</inf>O<inf>x</inf>:H is effective to improve the open circuit voltage of the solar cells. We also confirmed that the open circuit voltage (V<inf>oc</inf>) logarithmically increased with increasing the light intensity, and the enhancement of V<inf>oc</inf> improved with increasing the band gap of p-layer. These results indicate that wide-gap p-μc-Si<inf>1−x</inf>O<inf>x</inf>:H is promising for use as window layer in hetero-junction μc-Si:H solar cells.

Application of SnO 2 substrate to top cell for spectrum splitting type solar cell

We have developed a spectrum splitting type solar cell using a-Si and CIGS as the top and bottom cells, respectively. To increase its performance the top a-Si cell with high Voc and good response at the short wavelength has to be developed. Up to now ZnO has been used as the front TCO. However, since the band gap of ZnO is lower than the one of SnO2, it is better to use SnO2 instead of ZnO. Furthermore, in this splitting solar cell there is no need for front TCO to be much textured. Here we present a initial introduction how to apply commercial and hazy SnO2 to the top cell. Ar treatment has been used in order to flatten the surface of SnO2. As the results high Voc as high as 0.967V has been achieved with smoother SnO2 surface.