A 2D/3D heterojunction engineered for carbon-based hole-transport-layer-free perovskite solar cells

The formation of a two-dimensional (2D) perovskite layer on the top of three-dimensional (3D) perovskite has been demonstrated to be effective in reducing interfacial charge recombination and improving the performance and stability of perovskite solar cells (PSCs). However, it is difficult to fabricate a 2D/3D perovskite heterojunction with accurate composition and structure through a solution-only process, and the location of the 2D perovskite is also difficult to regulate owing to the uncontrolled cation exchange between organic constituents, which results in mismatched energy level arrangements. Herein, a 2D perovskite with a spacer cation of 1,4-dimethylphenylene ammonium is grown on 3D perovskite film by the solid-state heat-pressure method. The relevant growth process, light absorption ability, energy level regulation, and stability of the samples are systematically investigated. A broad range of experimental characterizations show that the introduction of 2D perovskite improves the energy level alignment with the adjacent carbon electrode and enhances the hydrophobic property of the perovskite sample. As a result, a remarkable power conversion efficiency (PCE) of 15.63% is achieved for the carbon-based hole-transport-layer-free PSCs based on 2D/3D heterojunction, which is higher than that of the control 3D device (11.88%). Simultaneously, the improved device retains 90% of its initial performance after aging for 1000 h in ambient conditions. The present work opens a new avenue for designing 2D/3D perovskite heterojunctions and improving the performance and stability of PSCs.