Highly Efficient and Stable Pure Two-Dimensional Perovskite-Based Solar Cells with the 3‑Aminopropionitrile Organic Cation

Pure two-dimensional (2D) perovskite (n = 1)-based perovskite solar cells (PSCs) have been proven to have excellent stability against humidity, but the photovoltaic performance is very poor due to the parallel orientation to the substrate and mismatched energy alignment in the PSC device. We report herein a novel bulky organic cation of 3-aminopropionitrile (3-APN) for constructing a pure 2D hybrid lead–iodide perovskite. The crystal structure of (3-APN)₂PbI₄ features a stable layered and undistorted PbI₆ octahedral geometry (∠Pb–I–Pb = 180°) with a small I···I distance (4.66 Å), and the crystals grow in a dominant out-of-plane direction to the substrate. In addition, the existence of an intramolecular H bond between cyano groups and ammonium heads result in an appropriate valence band level of (3-APN)₂PbI₄ for a well-matched energy level alignment in the device, benefitting the interfacial charge transfer and hence a better photovoltaic performance. As a result, the PSC with the pure 2D (3-APN)₂PbI₄ perovskite-based PSC achieves a power conversion efficiency of 3.39%, which is the highest value thus far for the pure 2D lead–iodide perovskite family, to the best of our knowledge. More importantly, this pure 2D (3-APN)₂PbI₄ perovskite-based PSC demonstrates excellent stability against humidity. This work demonstrates that there is great potential to realize efficient and stable pure 2D perovskite-based PSCs through the wise design of organic cations.