Suppressing Metallic Bi0 Defects in Pb-Free Rudorffite Indoor Photovoltaics via Hot-Air-Assisted Modulated Crystallization

Abstract

Perovskite solar cells contain Pb and have low stability, which limits their commercialization, particularly in indoor applications. Rudorffites (Ag_xBi_yI_x+3y) are promising Pb-free, stable absorbers for indoor photovoltaics. Hot air processing is facile, environmentally friendly, and suitable for large-scale manufacturing. This work introduces, for the first time, hot-air-processed rudorffite thin films. The AgBiI₄ thin films had a wide band gap (1.97 eV) and captured light within the spectrum of a white-light-emitting diode. Hot air processing reduced the amount of metallic Bi⁰, which suppressed recombination and reduced leakage current. Therefore, the performance parameters, including power conversion efficiencies (PCEs), of the hot-air-processed devices exceeded those of non-hot-air-processed devices. The optimal device achieved a stabilized output of 3.4% (11.1 μW/cm²) under 1000 lx. Under ambient conditions without encapsulation, the hot-air-processed devices retained 88.9% of their initial PCE under 1000 lx after 35 days. The improved performance and stability are correlated with the modulated crystallization of the solvated intermediate adducts.