A Universal Method of Perovskite Surface Passivation for CsPbX3 Solar Cells with VOC over 90% of the S-Q limit

In comparison to hybrid perovskite solar cells (PSCs), all-inorganic CsPbX3 PSCs suffer from larger V-OC deficits, leading to inferior efficiency. The perovskite surface defects like iodine vacancy (V-I) are the main sources of nonradiative recombination causing a V-OC deficit. Here, 2,5-thiophenedicarboxylic acid (TDCA) is used to passivate the surface V-I 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 V-OC 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 V-OC limit. This method also promotes the V-OC 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.