Highly conductive p-type nc-SiOX:H thin films deposited at 130°C via efficient incorporation of plasma synthesized silicon nanocrystals and their application in SHJ solar cells

Abstract

We present highly conductive and transparent p-type hydrogenated nanocrystalline silicon oxide (p-type nc-SiOX:H) layers produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) at 130°C and 150°C. We report on the crystalline volume fraction (XC), spectral broadening parameter C, and dark conductivity (σ) as functions of the growth temperature and RF power, and how these properties evolve with post-deposition annealing at 250°C and 300°C. Interestingly, we observe that the best layers in terms of crystalline volume fraction and conductivity are obtained at the lowest temperature and RF power, which we attribute to the soft landing of silicon nanocrystals synthesized in the plasma. The p-type nc-SiOX:H layers with the best properties on glass substrates are implemented as carrier-selective contacts in silicon heterojunction (SHJ) solar cells with the structure: (n) a-Si:H / (i) a-Si:H / n-type c-Si / (i) a-Si:H / (i) a-SiOX:H / (p) nc-SiOX:H / (p) nc-Si:H where all films are deposited by PECVD. The cells were completed with sputtered ITO on the front and rear sides plus Ag on the rear side, and Ag grid on the front, with the best devices showing conversion efficiencies of 21.8%, which, contrary to a-Si:H contact layers, are preserved or even slightly improved upon annealing at 240°C.