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

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 T₈₀ lifetime of ≈525 h has been obtained during the quasi-maximum power point tracking test in open air (device unsealed).