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

The all-inorganic CsPbI 2 Br material shows promise for indoor photovoltaics but suffers from a severe open-circuit voltage (V oc ) 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 PbI 2 , outcompeting DMSO and increasing the activation energy for CsPbI 2 Br nucleation. This yields CsPbI 2 Br 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 V oc 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 V oc deficit and instability of CsPbI 2 Br indoor photovoltaics.