Three‐Step Holistic Treatment on Carbon‐Electrode Based Low‐Temperature Mesoscopic Perovskite Solar Cells to Achieve PCE > 18% and T80 > 500 h in Open Air

Abstract Carbon‐ electrode (CE) based, hole‐conductor‐free mesoscopic perovskite solar cells (meso‐CPSCs) offer the merits of high stability and low cost, but they contain a large number of nanosized perovskite (PVSK) crystallites in the CE region. These crystallites contribute little to light absorption, but bring risks of charge recombination. Herein, a three‐step holistic treatment is introduced to address this issue, such as treatment‐1 (T1): partial CE peeling; treatment‐2 (T2): octylammonium iodide modification; and treatment‐3 (T3): coating of a secondary layer of CE. Low‐temperature meso‐CPSCs are chosen as the model platform to perform the strategy. It is observed that the strategy removes the redundant PVSK crystallites, induces the formation of tilt‐stacked two‐dimensional (2D) PVSK, and strengthens interfacial contact of PVSK/CE, which reduces the recombination risks and facilitates interfacial charge‐extraction, and finally elevates the power conversion efficiency (PCE) of the low‐temperature meso‐CPSCs from 14.25(±0.69)% to 16.05(±0.40)%(optimized to 17.28%). The efficiency is further upgraded to 18.07% after additional optimization on internal resistance and substrate transparency. Such performance achieves an increment of ≈50% when comparing to the efficiency of ≈12% that was firstly reported in 2020. In more, the T 80 lifetime of ≈525 h has been obtained during the quasi‐maximum power point tracking test in open air (device unsealed).