A low-cost hole transport layer enables CsPbI2Br single-junction and tandem perovskite solar cells with record efficiencies of 17.8 % and 21.4 %

Among all-inorganic perovskites, CsPbI2Br possesses excellent intrinsic thermal stability, suitable bandgap and superior phase-stability, demonstrating large application potential for single-junction perovskite solar cells (PSCs) and perovskite/organic tandem solar cells (TSCs). To further improve the power conversion efficiencies (PCEs) of CsPbI2Br PSCs and TSCs, in this work, a dopant-free low-cost polymer PTQ10 is used as hole transport layer (HTL) for PSC and inter-connecting layer (ICL) for TSC. Owing to better energy level matching between PTQ10 and CsPbI2Br than the classic P3HT, as well as the surficial passivation of perovskite induced by the functional groups of PTQ10, the CsPbI2Br PSC with PTQ10 HTL achieves a champion PCE of 17.8 % with a high open-circuit voltage (VOC) of 1.4 V. Moreover, the ICL employing PTQ10 HTL also exhibits excellent optical and electrical properties for the application in monolithic CsPbI2Br/organic TSC. As a result, TSCs using the CsPbI2Br as the front cell and PM6:Y6 (or D18:Y6) as the rear cell present the highest PCE of 21.4 % (21.3 %), with the record high VOC of 2.22 V. This work shows the excellent performance of PTQ10 as HTL in CsPbI2Br based PSCs and TSCs and demonstrates that the development of efficient HTL is essential to further improve the performance of PSCs and TSCs.