Study of Amorphous Silicon Based Thin-Film Solar Cells with Full Spectrum Splitting Technique

This thesis describes the results of research on the numerical analysis and elemental technology for full spectrum splitting thin-film solar cell to improve conversion efficiency. The first theoretical analyses of amorphous silicon solar cell are studied. The model of the solar cell structure assumes a p-i-n superstrate structure. For electrical and optical parameters were taken from experimental results and refered literature. Each layer using spectroscopic ellipsometry (SE) analysis results by using Tauc-Lorentz model. In order to investigate that how the devices structure influences the solar cell performance of a-Si:H solar cells under various parameter such as band gap, thickness. Then best performance solar cell parameter has been calculated and based on these parameter, spectrum splitting structure simulation has been studied. a-Si:H and CIGS cells are having thousands of variable parameters in the splitting structure. Among them, main parameters are considered to be the splitting wavelength, which is the exact number of wavelength that divided the solar spectrum into two parts or more, and band gap and thickness of absorber materials. The total efficiency under the different range of splitting wavelength. The total efficiency for the combination of the top cell with wider band gap and the bottom cell with narrow band gap shows higher total efficiency. In this simulation, when splitting wavelength is 600nm, we can obtain the best total simulated splitting efficiency of 24.1% (Eg = 2.0 eV, Jsc = 11.7 mA/cm2, Voc = 1200 mV, FF = 70 %, Eff. = 10.7 % for the top cell and Eg = 1.1 eV, Jsc = 27.9 mA/cm2, Voc = 607 mV, FF = 79 %, Eff. = 13.4 % for the bottom cell). It was found from the simulation that the total efficiency of nearly 25% can be obtained at the splitting wavelength of 600 nm with top cell using higher band gap material. The experiment has been carried out to verify the simulation results. The a-Si:H solar cells with i-layers having its band gap of 1.9 eV have been fabricated by 60 MHz VHF-PECVD with solar cell area of 0.086 cm2 . The cell structure basically is glass /TCO( ZnO:B, SnO2:F) / p-a-SiC:H / buffer / i-a-Si:H (1.9 eV, 300 nm) / n-μc-SiO:H / Ag / Al. In order to get wider band gap for a-Si:H solar cell, low temperature and high H2 dilution (ratio of SiH4/H2=8) have been employed while substrate temperature , inter-electrode distance, VHF power density and chamber pressure were kept constant at 150℃, 2 cm, 1 mW/cm2 and 50 Pa, respectively. Then this solar cell has been measured by spectrum splitting technique. As a result, the total efficiency of 22% has been developed as been guided by the simulation.

identifier:oai:t2r2.star.titech.ac.jp:50247879

identifier:oai:t2r2.star.titech.ac.jp:50247880