Achieving over 20 % Efficiency in Laminated HTM‐Free Carbon Electrode Perovskite Solar Cells through In Situ Interface Reconstruction

Abstract Laminating a free‐standing carbon electrode film onto perovskite film is a promising method for fabricating HTM (hole transport material)‐free carbon electrode perovskite solar cells (c‐PSCs), offering more flexibility by decoupling the processes of carbon electrode and perovskite layer formation. However, the power conversion efficiency (PCE) of laminated HTM‐free c‐PSCs (<16.5 %) remains lower compared to c‐PSCs with printed carbon pastes (>20 %), primarily due to poor interfacial contact between the perovskite and carbon layers. Herein, we report a chemical‐mechanical driven in situ interface reconstruction strategy to solve such interface contact issues. The in situ interface reconstruction is firstly triggered by methylammonium chloride (MACl) surface treatment to chemically activate the film and then mechanically laminate the carbon electrode onto the softened perovskite film under heating. The perovskite film undergoes in situ regrowth and the carbon film starts to cure simultaneously, dynamically reconstructing the perovskite/carbon electrode interface. A tighter and conformal contact is achieved, greatly facilitating the carrier transport and extract. Ultimately, a champion PCE of 20.31 % is achieved with enhanced stability. Our in situ interface reconstruction strategy which is combinating the chemical and mechanical process offers a new choice for the further design of low‐cost and efficient HTM‐free c‐PSCs.