Carbon-Based Hole Transport Layer-Free Perovskite Solar Cells with an Efficiency beyond 18% Boosted by a Methylammonium Chloride Additive

Carbon-based perovskite solar cells (C-PSCs) hold great prospects for commercialization due to their lower manufacturing cost and better stability when compared with metal electrode perovskite. Nevertheless, their power conversion efficiency (PCE) is lower than those of metal-based perovskite solar cells because of the inadequate interface contact between the carbon electrode and the perovskite layer. In this study, the hole transport layer (HTL)-free carbon-based perovskite configuration is utilized to further reduce the cost, and the methylammonium chloride (MACl) additive is introduced to passivate the defects of the perovskite and enhance the interface contact performance. The results indicate that the MACl additive can improve the crystal quality of the perovskite film, reduce the density of defect states, fill the vacancies of the iodide ion, and inhibit the formation of the δ-phase. The optimized C-PSC exhibits an increased carrier lifetime, resulting in improved stability and PCE, with a champion efficiency of 18.04%. Additionally, the device demonstrates ultrahigh photoelectrical stability during continuous light illumination. The unpackaged device with the MACl additive retained 80% of its initial PCE after being operated for 1000 h under double 85 conditions (i.e., at 85 relative humidity (RH) and 85 °C). This work provides an extremely effective strategy for optimizing the interface contact of carbon-based perovskites and preventing the formation of the δ-phase, thereby leading to more efficient and stable optoelectronic devices.