Dual Sub-Cells Modification Enables High-Efficiency n-i-p Type Monolithic Perovskite/Organic Tandem Solar Cells

Monolithic perovskite/organic tandem solar cells (POTSCs) have attracted increasing attention owing to ability to overcome the Shockley-Queisser limit. However, compromised sub-cells performance limits the tandem device performance, and the power conversion efficiency (PCE) of POTSCs is still lower than their single-junction counterparts. Therefore, optimized sub-cells with minimal energy loss are desired for producing high-efficiency POTSCs. In this study, an ionic liquid, methylammonium acetate (MAAc), is used to modify wide-bandgap perovskite sub-cells (WPSCs), and bathocuproine (BCP) is used to modify small-bandgap organic solar cells. The Ac- group of MAAc can effectively heal the Pb defects in the all-inorganic perovskite film, which enables a high PCE of 17.16% and an open-circuit voltage (V-oc) of 1.31 V for CsPbI2.2Br0.8-based WPSCs. Meanwhile, the BCP film, inserted at the ZnO/organic bulk-heterojunction (BHJ) interface, acts as a space layer to prevent direct contact between ZnO and the BHJ while passivating the surface defects of ZnO, thereby mitigating ZnO defect-induced efficiency loss. As a result, PM6:CH1007-based SOSCs exhibit a PCE of 15.46%. Integrating these modified sub-cells enable the fabrication of monolithic n-i-p structured POTSCs with a maximum PCE of 22.43% (21.42% certified), which is one of the highest efficiencies in such type of POTSCs.

Automated summary

This study uses an ionic liquid, methylammonium acetate (MAAc), and bathocuproine (BCP) to modify wide-bandgap perovskite sub-cells and small-bandgap organic solar cells. MAAc effectively heals the defects in the perovskite film, improving the energy conversion efficiency, while BCP acts as a space layer to prevent direct contact between ZnO and the organic bulk-heterojunction, mitigating efficiency loss. The integration of these modified sub-cells enables the fabrication of monolithic n-i-p structured tandem solar cells with a maximum PCE of 22.43%.