DEVELOPMENT OF NOVEL ULTRATHIN TUNNEL LAYERS FOR CARRIER SELECTIVE PASSIVATED CONTACTS IN SOLAR CELLS

Abstract

Tunnel layer passivated contacts have enabled low recombination losses and high energy conversion efficiencies for silicon solar cells. This work is aimed at investigating if the presence of high interface charge in tunnel layers can further enhance carrier selectivity of passivated contacts and in turn solar cell efficiencies. Novel material systems such as silicon oxide (SiOx), aluminium oxide (AlOx), and silicon nitride (SiNx) were systematically studied along with p-/n- doped polycrystalline silicon or low-temperature, dopant-free, organic PEDOT:PSS as the capping layer. Several process parameters were optimized i.e. (i) annealing conditions, (ii) surface pre-treatment, and (iii) tunnel layer thickness to maximize charge (and thus minimize recombination) and minimize tunnelling resistance. It is experimentally proven here that substitution of ultrathin SiOx by SiNx (high positive charge) or AlOx (high negative charge) aids the extraction of electrons or holes respectively and enhances the selectivity and efficiency potential of the passivated contact. Processed SiNx/n+-poly-Si and AlOx/PEDOT:PSS passivated contacts have measured efficiency potential of 28.3% and 25.9% which is 0.4% absolute and 1% absolute higher than using the reference SiOx tunnel layer.