Development of high conducting phosphorous doped nanocrystalline thin silicon films for silicon heterojunction solar cells application

Abstract

We have investigated the PECVD growth of the phosphorus-doped hydrogenated nanocrystalline silicon (n-nc-Si:H) film as an electron-selective layer in silicon heterojunction (SHJ) solar cells. The effect of power densities on the precursor gas dissociation are investigated using optical emission spectra and the crystalline fraction in n-nc-Si:H films are correlated with the dark conductivity. With the Pd of 122 mW/cm2 and ~2% phosphorus doping, we observed Raman crystallinity of 53%, high dark conductivity of 43 S/cm, and activation energy of ~23 meV from the ~30 nm n-nc-Si:H film. The n-nc-Si:H layer improves the textured c-Si surface passivation by two-fold to ~2 ms compared to the phosphorus-doped hydrogenated amorphous silicon (n-a-Si:H) layers. An enhancement in the open-circuit voltage and external quantum efficiency (from >650 nm) due to the better passivation at the rear side of the cell after integrating the n-nc-Si:H layer compared to its n-a-Si:H counterpart. An improvement in the charge carrier transport is also observed with an increase in fill factor from ~71 % to ~75 %, mainly due to a reduction in electron-selective contact resistivity from ~271 mΩ-cm2 to ~61 mΩ-cm2. Finally, with the relatively better c-Si surface passivation and carrier selectivity, a power conversion efficiency of ~19.90% and pseudo-efficiency of ~21.90% have been realized from the SHJ cells.