Indole‐2‐Carboxylic Acid Ligand‐Mediated Synthesis of Stable Perovskite Nanocrystals for Fast Responsive Photodetector

Abstract Cesium lead bromide perovskite nanocrystals (NCs) show great potential for photoelectric properties. However, due to their poor stability and the insulating nature of passivating ligands, they suffer from practical applications. Herein, in an approach to passivate the NCs surface by introducing a ligand, Indole‐2‐carboxylic acid (ICA), we synthesized a mixed CsPbBr 3 /Cs 4 PbBr 6 NCs by a ligand‐assisted reprecipitation approach. Incorporating the ICA ligand in place of long‐chain insulating Oleic acid (OA) effectively reduced the loss of nonradiative recombination induced by surface trap states. Through all the performed compositional and structural characterization, the existence of CsPbBr 3 /Cs 4 PbBr 6 mixed NCs was confirmed. The obtained CsPbBr 3 /Cs 4 PbBr 6 mixed NCs show green emission at 518 nm and superior stability under ambient conditions compared to CsPbBr 3 NCs. The photoluminescence (PL) of the CsPbBr 3 /Cs 4 PbBr 6 mixed NCs increased approximately three times, and the PL quantum yield (PLQY) increased from 75 ± 2% to 94 ± 2% as compared to CsPbBr 3 NCs. To demonstrate the potential application of the material in optoelectronics, a photodetector based on mixed CsPbBr 3 /Cs 4 PbBr 6 NCs is fabricated, which exhibits the maximum responsivity of 1.133 mA/W at 9 mW/cm 2 incident power density and faster rise and fall times of 0.31 ms and 1.19 ms, respectively. The specific detectivity of the device is 1.608 × 10⁹ Jones with an incident power of 9 mW/cm 2 .