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

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 x 10(11) Jones), and the ratio of current in dark to light (similar to 7160). These observations for Cs3Bi2Cl9 single crystals, which were optically active but showed retroactive photocurrent on irradiation, remain unique for such materials.

Automated summary

Lead-free Cs3Bi2Cl9 perovskite exhibits light-induced negative photoconductivity with slow recovery, attributed to the formation of light-activated metastable trap states within the crystal. Studies using femtosecond transient reflectance spectroscopy reveal the unique electronic transport properties of Cs3Bi2Cl9 single crystals, which show retroactive photocurrent upon irradiation. The figure of merits for Cs3Bi2Cl9 single-crystal detectors, including responsivity, detectivity, and current ratio, demonstrate the potential of this material for device applications.