Flexible Narrow Bandgap Sn–Pb Perovskite Solar Cells with 21% Efficiency Using N,N′-Carbonyldiimidazole Treatments

Abstract

Flexible tin−lead (Sn−Pb) mixed perovskite solar cells (PSCs) are among the promising flexible photovoltaics, owing to the narrow bandgap (NBG) of Sn−Pb perovskites, flexible and wearable features, and their role as a critical component in allperovskite tandem photovoltaics. However, the flexible Sn−Pb PSCs suffer from a low power conversion efficiency, no higher than 18.5%, along with limited stability. Herein, we reported an efficient and stable flexible NBG Sn−Pb PSC via an N,N′-carbonyldiimidazole (CDI) passivation strategy. CDI, with strong adsorption energy, preferentially binds to Sn 2+ compared with oxygen (O 2 ), thus effectively inhibiting the adsorption of O 2 on perovskite surfaces. The transfer of electron density around Sn 2+ dramatically decreased, thus suppressing Sn 2+ oxidation. The CDI treatments endowed the Sn−Pb mixed films with fewer defects, improved crystallinity, better morphology, and matched energy-level alignment. The flexible Sn−Pb devices exhibited a high PCE of 21.02%. Besides, the devices showed enhanced stability and promoted flexibility. This work provides a pathway to visibly increase the efficiency and stability of the flexible Sn−Pb mixed photovoltaic cells.