Effect of thermal annealing on the optical and electrical properties of boron doped a-SiOx:H for thin-film silicon solar cell applications

Abstract

The p-type layer in a p-i-n thin-film solar cell plays a crucial role in determining efficiency. The requirements for p-type layer films are high optical band gap (Eg), narrow valence band tail to minimize optical absorption, high dark conductivity, and low activation energy to reduce the parasitic series resistance of the solar cell. We investigated the effects of temperature during film growth and post-deposition thermal annealing on the optical and electronic properties of p-type amorphous silicon oxide films (p-a-SiOx:H) for thin-film silicon solar cell applications. The activation energy of thermally annealed p-a-SiOx:H film prepared at low substrate temperature decreased from 0.72eV to 0.56eV with similar Eg. Our improvements are explained in the changed ratio of conjugation with the three- and four-fold coordinated boron atoms by the shift of the B (1s) X-ray photoelectron spectrum. Taking into account the reversible electrical change by thermal annealing while maintaining high optical properties, we propose necessary process-procedure conditions for obtaining high photovoltaic performance in thin-film-Si solar cells with high-quality p-a-SiOx:H. We carried out device modeling of p-i-n junction amorphous silicon solar cells by employing a thermal annealing effect on p-type a-SiOx:H layer, using an advanced semiconductor analysis simulator. Due to reduced Ea with high Eg of p-type a-SiOx:H layer after thermal annealing, the solar cell performance of the open circuit voltage, fill factor, and conversion efficiency improved by 11.1%, 60.42%, and 53.75%, respectively.