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

Perovskite solar cells contain Pb and have low stability, which limits their commercialization, particularly in indoor applications. Rudorffites (Ag x Bi y I x +3 y ) 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 AgBiI 4 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 Bi 0, 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/cm 2 ) 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.