In comparison to hybrid perovskite solar cells (PSCs), all‐inorganic CsPbX3 PSCs suffer from larger VOC deficits, leading to inferior efficiency. The perovskite surface defects like iodine vacancy (VI) are the main sources of nonradiative recombination causing a VOC deficit. Here, 2,5‐thiophenedicarboxylic acid (TDCA) is used to passivate the surface VI through the strong coordination interaction between the thiophene unit of TDCA and the undercoordinated Pb2+ of perovskite. TDCA passivation also elevates the perovskite surface valence band position, leading to a better interfacial energy alignment. Consequently, the VOC of CsPbI2.25Br0.75 PSCs is remarkably improved from 1.36 to 1.43 V (efficiency from 15.55% to 16.72%), reaching 92% (record‐high among CsPbX3 PSCs) of the Shockley–Queisser VOC limit. This method also promotes the VOC of CsPbI1.5Br1.5 cell from 1.42 to 1.51 V (90% of the limit) and CsPbIBr2 cell from 1.44 to 1.54 V (87% of the limit), demonstrating its universality for CsPbX3 perovskites.
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Zhao et al. (2022) studied this question.