Managing Crystallization of CsPbI2Br Films for High-Performance Indoor and Outdoor Photovoltaics

The all-inorganic CsPbI2Br material shows promise for indoor photovoltaics but suffers from a severe open-circuit voltage (Voc) deficit under low light due to defect-mediated recombination. Here, we introduce 3,4-thiophenedicarboxylic anhydride (TDA) into the precursor solution to synergistically retard crystallization and passivate defects. Density functional theory and synergistic experiments confirm that TDA strongly coordinates with PbI2, outcompeting DMSO and increasing the activation energy for CsPbI2Br nucleation. This yields CsPbI2Br films with larger grains, enhanced crystallinity, and reduced trap density. Residual TDA molecules can passivate uncoordinated Pb2+ at grain boundaries, suppressing nonradiative recombination. Using a dopant-free P3HT hole-transport layer, the optimized device achieves a champion power conversion efficiency (PCE) of 17.33% with a remarkable Voc of 1.42 V under standard illumination. Under 1000 lux LED indoor light, the device delivers a PCE of 36.22%. More importantly, TDA-optimized devices can retain 90% of initial efficiency after 1500 h in ambient air and 90% after 1000 h at 85 °C. This work provides a facile strategy to overcome the Voc deficit and instability of CsPbI2Br indoor photovoltaics.