SnO 2 is widely used and one of the most efficient electron transport layers in perovskite solar cells (PSCs). However, SnO 2 films often contain detrimental defects and may also have mismatches in energy level alignment with perovskite films, thus limiting the open-circuit voltage (V OC ). Managing the defects and band structure are critical to reduce energy loss in PSCs. Herein, cobalt chloride hexahydrate (CoCl 2 •6H 2 O) is introduced into a SnO 2 film, which shows favorable energy level alignment and better charge extraction. Correspondingly, an enhanced V OC up to 1.20 V was achieved along with an efficiency of 23.82%, which is the record open-circuit voltage at the optical band gap of 1.54 eV in planar structure PSCs. Moreover, the target devices show enhanced stability, which retains 83.5% of their initial efficiencies after 200 h under continuous irradiation. The doping method provides an effective strategy for reducing energy loss to further enhance the efficiency of PSCs.

In recent years, perovskite/silicon tandem solar cells (PK/c‐Si tandem) have demonstrated high power conversion efficiency (PCE) and demonstrated great application potential in photovoltaic (PV) systems. However, the PCE of PK/c‐Si tandem devices is still below the theoretical limit. From a broader perspective, their poor stability and difficulty in large‐area realization are crucial barriers for commercial viability. In this report, the detailed constraints facing high PCE of tandem devices and the corresponding solutions are discussed. The authors propose that the main obstacle comes from the limitation of the perovskite top cell. However, careful understanding of the optical and electrical properties of each functional layer is expected to be the core process to further promote efficiency. Regarding the environmental and intrinsic instability issues, encapsulation is considered to be the most effective method to address environmental instability. Preventing ion migration is one of the fundamental methods to eliminate intrinsic instability. It is believed that low dimensional perovskite materials will become a competitive solution to simultaneously solve these two instabilities. Finally, some suggestions for reducing costs and preparation of PK/c‐Si tandem on a large‐scale are also discussed which provides guidance for further boosting the development of PK/c‐Si tandem.

The perovskite/silicon tandem solar cell (PK/c‐Si TSC) is a reasonable choice that can break through the efficiency limitations of silicon cells. Here, the p‐i‐n perovskite solar cell is conformally grown by the evaporation–solution combination technique on fully‐textured silicon heterojunction cells to realize two‐terminal PK/c‐Si TSCs. Due to the adverse effect of the residual PbI2 at the bottom of the perovskite bulk on device performance, a thermal‐evaporated CsBr thin layer is introduced between the perovskite layer and the hole transport layer to construct a gradient perovskite absorber for optimized energy level alignment, so as to improve the open‐circuit voltage and fill factor of the device. Finally, the PK/c‐Si tandem cell achieves an efficiency of 27.48% and is stable in nitrogen over 10 000 h.