Fabrication of Highly Efficient and Stable Hole‐Transport Material‐Free Perovskite Solar Cells through Morphology and Interface Engineering: Full Ambient Process

Carbon‐based hole‐transport material (HTM)‐free perovskite solar cells (PVSCs) with low cost and high stability attract research interest. Herein, a facile way to improve the performance of HTM‐free PVSCs by employing two strategies is reported: first, adding a small amount of tetrahydrofuran (THF) in lead iodide (PbI 2 )/ N , N ‐dimethylformamide (DMF) solution to improve the quality of the perovskite film; second, introducing an ultra‐thin Al 2 O 3 film at the interface of TiO 2 /perovskite to reduce charge recombination. THF is found to facilitate the formation of homogenous perovskite films with better coverage, while the ultra‐thin Al 2 O 3 layer avoids the direct contact of TiO 2 with CH 3 NH 3 PbI 3 . The Al 2 O 3 layer can effectively block holes and prevent charge recombination, thus leading to a dramatic improvement of open‐circuit voltage and fill factor in PVSCs. Moreover, the PVSCs show excellent long‐term stability with no degradation for 1000 h under ambient conditions. A facile way for the future commercialization of efficient low‐cost HTM‐free PVSCs is provided.