Comparative study of different silicon oxides used as interfacial passivation layer (SiNy:H / SiOx /n+-Si) in industrial monocrystalline silicon solar cells

Abstract

Ultrathin silicon oxide (SiOx) is used as a passivating and tunneling layer in high efficiency passivated contact silicon (Si) wafer solar cells. In this work, the emitter surface passivation quality using a low-cost, low-temperature (40 °C), non-acidic and safe chemical oxide passivation process (named as NCPRE-oxide) grown using sodium hypochlorite solution is compared with other existing oxide growth or deposition processes such as dry thermal oxide, Radio Corporation of America standard clean-2 (RCA-2) chemical oxide, nitric acid based oxide, sulphuric acid based (Piranha) oxide, ozone based oxide and deposited oxide by plasma enhanced chemical vapour deposition on standard 6-inch textured Si wafers. All the oxides layers are capped with hydrogenated amorphous silicon nitride (SiNy:H) improve passivation of the n+-type Si surface. There is a substantial improvement in the effective minority carrier lifetime (τeff) for SiOx/SiNy:H stack on the phosphorous diffused pyramidal textured Si surface. Further, to compare the influence of NCPRE-oxide process with other oxide processes on the electrical performance of the final device, these different processes were included in the fabrication of large area industrial aluminum-back surface field (Al-BSF) solar cells. A comprehensive analysis based on ellipsometry for film thickness measurement, τeff measurement, cell current-voltage characteristics, photoluminescence imaging, internal quantum efficiency mapping, and front surface recombination velocity measurement is presented. The NCPRE-oxide process resulted in a similar improvement in passivation and cell efficiency as other oxide processes for Al-BSF cells. In addition, its low-cost, low thermal budget, easy waste disposal, and single-component nature make it viable for industrial scale implementation.