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The poor film stability of Sn-Pb mixed perovskite film and the mismatched interface energy levels pose significant challenges in enhancing the efficiency of tin–lead (Sn-Pb) mixed perovskite solar cells. In this study, polyvinylpyrrolidone (PVP) is introduced into the PVK perovskite precursor solution, effectively enhancing the overall stability of the film. This improvement is achieved through the formation of robust coordination bonds between the carbonyl (C=O) in the pyrrole ring and the undercoordinated SnII and PbII, thereby facilitating the passivation of defects. Furthermore, the introduction of PVP inhibits the oxidation of tin (Sn), thereby enhancing the n-type characteristics of the perovskite film. This adjustment in the energy level of the PVK perovskite film proves instrumental in reducing interface energy loss, subsequently improving interface charge transfer and mitigating device recombination. Consequently, perovskite solar cells incorporating PVP achieve an outstanding champion power conversion efficiency (PCE) of 21.31%. [ABSTRACT FROM AUTHOR]

Efficient electron transport layer-free perovskite solar cells (ETL-free PSCs) are promising designs because they offer low-cost, simpler device configuration and greatly promote the large area flexible application of PSCs. Meanwhile, compared to traditional PSCs with ETL, the development of ETL-free PSCs is hindered by their low performance due to serious interfacial energy loss. Herein, we reveal that ETL-free devices with relatively low carrier lifetimes of perovskite films exhibit more substantial photogenerated carrier loss, resulting in a lower electron-injection rate at the FTO (fluorine-containing tin oxide)/perovskite interface, which is mainly responsible for the performance loss. Moreover, we demonstrate that improving the carrier lifetimes of perovskite films can remedy the poor carrier extraction efficiency at the FTO/perovskite interface through three typical perovskite films. Similarly, for all-inorganic perovskite with lower carrier lifetime and hole transport layer-free devices, prolonging carrier lifetime may be an important measure to improve the device performance. Benefiting from this discovery, increasing the carrier lifetime of the perovskite films can counterbalance the inferior device interfaces, endowing the ETL-free PSCs with high performance close to that of the ETL devices. Our research provides insights into ETL-free PSCs and offers opportunities for high-performance ETL-free PSC device design. [ABSTRACT FROM AUTHOR]

CsPbI2Br all-inorganic perovskite solar cells (PSCs) have attracted much attention due to their suitable bandgap and outstanding thermostability. However, the large energy loss of CsPbI2Br PSCs generally endows low open circuit voltage (VOC) and unsatisfactory power conversion efficiency (PCE), which severely hamper its further development. Herein, we proposed a facile route to modify the ZnO electron transporting layer (ETL) by in situ chemical doping strategy with metal ions. The doped ZnO ETL with Pb(Ac)2 or CsAc cannot only effectively tune its energy levels, conductivity, and charge extraction but also ameliorate the crystallization and morphology of upper perovskite films. Particularly, Pb(Ac)2-doped ZnO (ZnO:Pb) induces an energy level offset of 0.15 eV relative to the conduction band of CsPbI2Br with largely reduced Ohmic loss. Thus, the highest VOC is significantly boosted to above 1.3 V for the CsPbI2Br PSCs with a champion PCE of 16.36%, while the reference PSC just yields a moderate PCE of 14.43% with a low VOC of 1.168 V. Moreover, considerable improvements in device stability are achieved for the PSCs with doped ZnO ETLs than those of the ZnO-based device. Our work provides a promising strategy to alleviate the VOC deficit toward the attainment of highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]