Optical properties of porous Si/PECVD SiN_X:H reflector on single crystalline Si for solar cells

The improvement of optical confinement on the back crystalline silicon solar cell is one of the factors leading to its better performance. Porous silicon (PS) layer can be used as a back reflector (BR) in solar cells. In this work, single layers of porous silicon were grown by electrodeposition on a single crystalline silicon substrate. The measurement of the total reflectivity (R_T) on Si/PS surface showed a significant improvement in optical confinement compared to that measured on Si/standard Al back surface field (BSF). The internal reflectivity (R_B) extracted from total reflectivity measurements achieved 86 % for the optimized single PS layer (92 nm thick layer with 60 % porosity) in the wavelength range between 950 and 1200 nm. This improvement was estimated as more than 17 % compared to that measured on the surface of Si/BSF Al contact. To improve the stability and passivation properties of PS layer BR, silicon nitride layer (SiN_x) was deposited by PECVD on a PS layer. The maximum measured total reflectivity for PS/SiNx achieved approximately 56 % corresponding to an improved R_B of up to 83 %. The PS formation process in combination with the PECVD SiN_x, can be applied in the photovoltaic cell technology and offer a promising technique to produce high-efficiency and low-cost c-Si solar cells.