Suppressing Multi-Dimensional Defects in Cs_0.05FA_0.95PbI₃ Single Crystals Enables Efficient and Stable Back-Contacted...

Back-contacted architectures offer cost and stability advantages for perovskite solar cells (PSCs), yet their efficiencies have plateaued at ∼12% due to defect-induced recombination and limited carrier diffusion in thin single crystals. Herein, a multi-dimensional defect suppression strategy is reported to overcome this bottleneck by incorporating N-methylformamidinium (MFA⁺) into Cs_0.05FA_0.95PbI₃ (FA = CH(NH₂)₂ ⁺) crystals. MFA⁺ strengthens interaction between A-site cations with iodide ions, thereby suppressing iodide vacancies (point defects), relieving tensile microstrain, and eliminating dislocations and surface wrinkles (line and plane defects). This approach yields high-quality crystals with extended electron diffusion lengths (∼400 µm). As a result, an impressive efficiency of 17.35% is obtained, representing a substantial advance over reported back-contacted PSCs. Moreover, the devices exhibit excellent operational stability with no performance degradation after 1350 h of continuous light illumination. This work highlights the importance of suppressing multi-dimensional defects for enhancing carrier transport, which is instructive for developing efficient back-contacted PSCs.