Suppressing weak-light voltage attenuation in Sb₂S₃ indoor photovoltaics using Li-doped TiO₂ layer

Antimony sulfide (Sb₂S₃) thin film have a suitable band gap (1.73 eV) and high absorption coefficient, indicating potential prospects in indoor photovoltaics. The open-circuit voltage (V_OC) attenuation under indoor weak light limits the performance and application, which is affected by the heterojunction interface quality. Hence, we propose a hole transport layer free Sb₂S₃ indoor photovoltaic cell using Li-doped TiO₂ as the electron transport layer to overcome weak-light V_OC loss. The Li-doped TiO₂ films prepared by spray pyrolysis LiCl additive precursor reveal higher surface potentials, enhancing electron collections. The doped interface also promoted subsequent grain growth of Sb₂S₃ thin film. The champion device, configured as FTO/TiO₂:Li/Sb₂S₃/Au, achieves an efficiency of 6.12% with an optimal Li doping ratio of 8% in the TiO₂ layer. The Li introduction at the junction interface suppresses the photocarrier recombinations under indoor light, thus improving device performance. The indoor power conversion efficiency of the Li-TiO₂ based Sb₂S₃ device reaches 12.7% under the irradiation of 1000-lux LED, showing 48% improvement compared with the undoped device. The Li-doped TiO₂/Sb₂S₃ photovoltaic device demonstrates significant advantages, particularly in cold and monochromatic light conditions, opening new prospects for indoor application.