The analysis of light trapping and internal quantum efficiency of a solar cell with grating structure

A multiple light paths analysis of the internal quantum efficiency (IQE) of a silicon solar cell with back reflector using grating structure to improve the light trapping is presented and the contributions of diffusion length of base regions to IQEs are simulated. An optical model for the determination of generation profiles of the cell is adopted and for a refractive index n material up to 4n2 light paths are considered and compared with no light trapping structure. It is found that the spatial widths of the cell, the increase of diffusion length, the diffraction angle distribution, number of light trapping paths and transmitted angle can significantly affect the IQEb for lower absorption wavelength (i.e., 1000-1100 nm). With 4nSi2 light trapping paths, the simulation results show that the best IQEs (≈IQEb) with transmitted angle can reach up to 73% which is 14% more than that with normal incident, the best achievable IQEb with grating structure is 49% at cell thickness wb = 50 μm, and the IQEb with diffraction angle θm = 60° is 9% and 39% larger than that with transmitted angle θl = 0° and without light trapping, respectively. For the case of normal transmitted angle, the IQEb with diffusion length 1000 μm is about 81% and is 37% higher than that with diffusion length 25 μm. The obtained results can provide essential information for designing a high-efficiency solar cell.