Assessing the Impact of Defects on Lead-Free Perovskite-Inspired Photovoltaics via Photoinduced Current Transient Spectroscopy

The formidable rise of lead-halide perovskite photovoltaics has energized the search for lead-free perovskite-inspired materials (PIMs) with related optoelectronic properties but free from toxicity limitations. The photovoltaic performance of PIMs closely depends on their defect tolerance. However, a comprehensive experimental characterization of their defect-level parameters—concentration, energy depth, and capture cross-section—has not been pursued to date, hindering the rational development of defect-tolerant PIMs. While mainstream, capacitance-based techniques for defect-level characterization have sparked controversy in lead-halide perovskite research, their use on PIMs is also problematic due to their typical near-intrinsic character. This study demonstrates on four representative PIMs (Cs₃Sb₂I₉, Rb₃Sb₂I₉, BiOI, and AgBiI₄) for which Photoinduced Current Transient Spectroscopy (PICTS) offers a facile, widely applicable route to the defect-level characterization of PIMs embedded within solar cells. Going beyond the ambiguities of the current discussion of defect tolerance, a methodology is also presented to quantitatively assess the defect tolerance of PIMs in photovoltaics based on their experimental defect-level parameters. Finally, PICTS applied to PIM photovoltaics is revealed to be ultimately sensitive to defect-level concentrations <1 ppb. Therefore, this study provides a versatile platform for the defect-level characterization of PIMs and related absorbers, which can catalyze the development of green, high-performance photovoltaics.