Inhibition of Pb0/I0 by polyoxometalate-driven redox strategy enables efficient and stable perovskite solar cells

Persistent illumination inevitably leads to the formation of Pb⁰ and I⁰ species in perovskite film, serving as non-radiative recombination centers and thus limiting the process of the commercial application. Herein, we propose a redox strategy to dynamically eliminate the defective Pb⁰ and I⁰ generated during device operation using polyoxometalate (POM) as an additive. Benefiting from the reversible W^5+/6+ redox activity and the structural stability when accepting and donating electrons from perovskite film, POMs play a role of the redox shuttle that oxidizes Pb⁰ into Pb²⁺ and reduces I⁰ into I⁻, consequently inhibiting the formation of Pb⁰ and I⁰ species and reducing the film defects, which benefits the improvement of stability and performance. As a result, the efficiency of carbon-based all-inorganic CsPbI₂Br cell is significantly improved to 15.12% and the efficiency of the organic-inorganic hybrid (Cs_0.05MA_0.05FA_0.9)Pb(I_0.93Br_0.07)₃ cell is also increased to 24.20%. More importantly, the target device shows superior stability under air conditions after storage for 1500 h, high temperature after 750 h, and persistent irradiation over 200 h, respectively, providing a new method for efficient and stable perovskite solar cells.