Molecule-triggered strain regulation and interfacial passivation for efficient inverted perovskite solar cells

Residual tensile strain impedes the improvement of efficiency and intrinsic stability of perovskite solar cells (PSCs), resulting from the perovskite lattice distortion and different thermal expansion coefficients. Herein, we propose a molecule-triggered strain regulation and interfacial passivation strategy to enhance the efficiency and stability (especially photostability) of PSCs, which utilizes the [2 + 2] cycloaddition reaction of 6-bromocoumarin-3-carboxylic acid ethyl ester (BAEE), consuming the incident UV light to suppress the tensile strain evolution. Meanwhile, the BAEE can form a strong bond with NiO_x, assisting the perovskite growth and the interface defect passivation. We obtain the efficiency of 26.32% (certified 26.08%), the open-circuit voltage (V_oc) up to 1.201 V with low V_oc loss (0.342 V), as well as the long-term stability (continuous 365 nm UV illumination: T₉₀ > 110 h in N₂, T₉₀ > 6 h in ambient air, and continuous LED white light irradiation at 100 mWcm⁻²: T₉₀ > 1,000 h).