Buried Interface Optimization for Flexible Perovskite Solar Cells with High Efficiency and Mechanical Stability.

The power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) are significantly reduced by defect-induced charge non-radiative recombination. Also, unexpected residual strain in perovskite films leads to an unfavorable impact on the stability and efficiency of PSCs, notably flexible PSCs (f-PSCs). Considering these problems, a thorough and effective strategy is proposed by incorporating phytic acid (PA) into SnO 2 as an electron transport layer (ETL). With the addition of PA, the Sn inherent dangling bonds are passivated effectively and thus enhance the conductivity and electron mobility of SnO 2 ETL. Meanwhile, the crystallization quality of perovskite is increased largely. Therefore, the interface/bulk defects are reduced. Besides, the residual strain of perovskite film is significantly reduced and the energy level alignment at the SnO 2 /perovskite interface becomes more matched. As a result, the champion f-PSC obtains a PCE of 21.08% and rigid PSC obtains a PCE of 21.82%, obviously surpassing the PCE of 18.82% and 19.66% of the corresponding control devices. Notably, the optimized f-PSCs exhibit outstanding mechanical durability, after 5000 cycles of bending with a 5 mm bending radius, the SnO 2 -PA-based device preserves 80% of the initial PCE, while the SnO 2 -based device only remains 49% of the initial value.