Constructing n/n − Type Perovskite Homojunctions to Achieve High‐Efficiency and Stable Printable Mesoscopic Perovskite Solar Cells

In recent years, carbon-based printable mesoscopic perovskite solar cells (p-MPSCs) without hole transport layers have garnered considerable interest because of their outstanding benefits in terms of stability and cost. However, the use of carbon electrodes instead of hole transport materials and noble metal electrodes leads to energy level mismatch, which limits the power conversion efficiency (PCE) of p-MPSCs. In this work, a molecular doping strategy is proposed employing cyclopentylmethanamine to passivate surface and subsurface crystal defects in perovskite layers while inducing an energy shift toward the p-type in the perovskite region within carbon electrodes. This approach facilitates the formation of a perovskite homojunction at carbon micro-interfaces between carbon electrodes and perovskites. Results demonstrate that the formation of this homojunction optimizes the internal energy level alignment of devices, thereby increasing driving force for hole transfer to carbon electrodes. Ultimately, the devices optimized through this strategy increase the PCE from 17.50% to 19.50% while retaining over 92% of the initial PCE after over 150 days in air ambiance. This study provides a straightforward and effective approach for designing high-efficiency and stable p-MPSCs.