Bi doping of Sb2S3 light-harvesting films: Toward suitable energy level alignment and broad absorption for solar cells

Sb2S3 has attracted widespread attention as a photovoltaic absorber material owing to its excellent photoelectric properties. However, the performance of Sb2S3-based solar cells is partly limited by its inappropriate band structure, such as deep valence band maximum (VBM) and wide bandgap, which critically lowers hole extraction efficiency and sets a threshold for attainable short-circuit current density (Jsc). Herein, a cationic bismuth-doping is applied to manipulate the energy level of Sb2S3 film by a hydrothermal process. As a result, the alloyed (Bi, Sb)2S3 delivers a redshift of absorption edge and an upshifted VBM, which are in line with our first-principles calculation. The optimized band structure markedly increases the light-harvesting and hole extraction efficiency. Additionally, the suitable doping of Bi also enhances grain size and preferred [hk1] orientation of absorber layer, consequentially favoring the carrier transport. Finally, this Bi-doping tactic boosts the device efficiency from 3.98 to 5.20% and Jsc from 12.58 to 15.38 mA/cm2 compared with pristine Sb2S3. This work paves an avenue for cationic-doping strategy in Sb2S3 solar cell.