Evaporated, Semitransparent Rudorffite AgBiI₄ Films for Pb-Free Indoor Photovoltaics

The toxicity of Pb continues to pose a significant risk to the commercialization of perovskite solar cells, particularly in indoor applications. Rudorffite Ag_xBi_yI_x+3y (ABI) with wide bandgap emerges as a promising Pb-free absorber for indoor photovoltaics. Vapor processing allows for precise thickness control, easy multilayer film formation, and the potential for large-scale production. This study introduces the photovoltaic performance of devices employing vapor-processed ABI thin films under indoor light illumination for the first time. The hexagonal rudorffite AgBiI₄ thin films, possessing a bandgap of 1.89 eV, were produced via sequential evaporation of BiI₃ and AgI, effectively capturing the spectrum of the white light-emitting diode. Moreover, the transmittance of these ∼65 nm thick AgBiI₄ thin films demonstrates their potential in semitransparent devices. Devices with these evaporated, semitransparent AgBiI₄ absorbers achieved a power conversion efficiency of 2.12% (7.02 μW/cm²) under 1000 lx. The stability of these devices was tested in an ambient atmosphere without encapsulation. Accelerated degradation was observed under 1000 lx compared to 1 sun, indicating increased sensitivity to aging under low light intensities.