17.3% Efficiency CsPbI2Br Solar Cells by Integrating a Near-infrared Absorbed Organic Bulk-heterojunction Layer

All-inorganic perovskite solar cells (PSCs) have gained extensive attention owing to the excellent intrinsic thermal stability, but their power conversion efficiencies (PCEs) still lag behind those of organic-inorganic hybrid PSCs due to their relatively wide bandgap. To extend the absorption of CsPbI2Br based all-inorganic PSCs, in this work, a low bandgap organic active layer of PM6:Y6 is integrated on the top of CsPbI2Br layer. Compared with CsPbI2Br PSCs using PM6 as hole transport layer, the integrated solar cells (ISCs) obtained an extended photo-response range to 950 nm and improved short-circuit current density (JSC) from 14.25 to 15.44 mA cm-2, as well as promoted PCE from 15.31% to 17.33%. Furthermore, the photoluminescence (PL), time-resolved-photoluminescence (TRPL), photoinduced transient absorption spectroscopy (TAS), transient photocurrent (TPC), and transient photovoltage (TPV) results demonstrate the effective carriers' bidirectional transport and suppressed carriers' recombination at CsPbI2Br/PM6:Y6 interface, which is the basis for ISCs to obtain high efficiency. Our findings demonstrate that ISC is a promising strategy to extend the photo-response range and improve the performance of CsPbI2Br based PSCs, and give a deeper understanding of carrier transfer in ISCs.