Microstructure and lateral conductivity control of hydrogenated nanocrystalline silicon oxide and its application in a-Si:H/a-SiGe:H tandem solar cells**Project supported by the Hi-Tech Research and Development Program of China (Grant No. 2013AA050302), the National Natural Science Foundation of China (Grant No. 61474065), Tianjin Municipal Research Key Program of Application Foundation and Advanced Technology, China (Grant No. 15JCZDJC31300), the Key Project in

Abstract

Phosphorous-doped hydrogenated nanocrystalline silicon oxide (n-nc-SiOx:H) films are prepared via radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Increasing deposition power during n-nc-SiOx:H film growth process can enhance the formation of nanocrystalline and obtain a uniform microstructure of n-nc-SiOx:H film. In addition, in 20s interval before increasing the deposition power, high density small grains are formed in amorphous SiOx matrix with higher crystalline volume fraction (Ic) and have a lower lateral conductivity. This uniform microstructure indicates that the higher Ic can leads to better vertical conductivity, lower refractive index, wider optical band-gap. It improves the back reflection in a-Si:H/a-SiGe:H tandem solar cells acting as an n-nc-SiOx:H back reflector prepared by the gradient power during deposition. Compared with the sample with SiOx back reflector, with a constant power used in deposition process, the sample with gradient power SiOx back reflector can enhance the total short-circuit current density (Jsc) and the initial efficiency of a-Si:H/a-SiGe:H tandem solar cells by 8.3% and 15.5%, respectively.