Simulation, design and fabrication of one-dimensional photonic crystal back reflector for silicon thin film solar cell

A new type of high-performance back reflector based on one-dimensional photonic crystal (1D PC) is introduced in this paper. The 1D PC is designed by alternately depositing a-Si and a-SiOx layers. Firstly the influences of refractive index, layer-thickness and corresponding periodicity on the band-gap of 1D PC are simulated using the finite difference time domain method. Based on the simulation results 1D PCs with different bandgaps are experimentally deposited. Just by adjusting the a-Si layer thickness, the high-reflection bandgaps in ranges of 500-750 nm and 650-1100 nm are easily achieved. The reflectivity values of 96.4% and 99% in the above-mentioned bandgaps are obtained. Comparing with the cells without a back reflector, a relative enhancement of 18.3% and 15.2% can be achieved for the short circuit current densities of a-Si:H single-junction and a-Si:H/μc-Si:H tandem solar cells, respectively, by integrating the above optimized 1D PC in the back. Also the influences of incident angles of white light, TE waves and TM waves on the reflectivity of 1D PC are studied using a software to generate spectrophotometric and ellipsometric spectra of a thin film stack. It is found that the reflectivity of 1D PC in solar cell is less affected by the changes of incident angles from air.