Dark Self-Healing-Mediated Negative Photoconductivity of a Lead-Free Cs₃Bi₂Cl₉ Perovskite Single Crystal

Abstract

Recently, halide perovskites have emerged as a promising material for device applications. Lead-based perovskites have been widely explored, while investigation of the optical properties of lead-free perovskites remains limited. Lead-halide perovskite single crystals have shown light-induced positive photoconductivity, and as lead-free perovskites are optically active, they are expected to demonstrate similar properties. However, we report here light-induced negative photoconductivity with slow recovery in lead-free Cs₃Bi₂Cl₉ perovskite. Femtosecond transient reflectance (fs-TR) spectroscopy studies further reveal that these electronic transport properties are due to the formation of light-activated metastable trap states within the perovskite crystal. The figure of merits were calculated for Cs₃Bi₂Cl₉ single-crystal detectors, including responsivity (17 mA/W), detectivity (6.23 × 10¹¹ Jones), and the ratio of current in dark to light (∼7160). These observations for Cs₃Bi₂Cl₉ single crystals, which were optically active but showed retroactive photocurrent on irradiation, remain unique for such materials.