Solution-based heteroepitaxial growth of stable mixed cation/anion hybrid perovskite thin film under ambient condition via a scalable crystal engineering approach

The performance of perovskite solar cells is under direct control of the perovskite film quality and controlling the crystalinity and orientation of solution-processed perovskite film is a fundamental challenge. In this study, we present a scalable fabrication process for heteroepitaxial growth of mixed-cation hybrid perovskites (FA1-x-yMAxCsy)Pb(I1-xBrx)3 in ambient atmospheric condition by using a Crystal Engineering (CE) approach. Smooth and mesoporous thin film of pure crystalline intermediate phase of PbX2.2DMSO is formed by deposition of supersaturated lead/cesium halides solution. Kinetically fast perovskite nucleation is achieved by rapid intercalation of formamidinium iodide (FAI) and methylammonium bromide (MABr) into the intermediate layer trough solvent assisted SN1 ligand exchange. Finally, heteroepitaxially perovskite growth is accomplished via Volmer−Weber crystal growth mechanism. All the layers are deposited under atmospheric condition (relative humidity (RH) 50–75%) with high reproducibility for various device and module dimensions. In particular, perovskite solar modules (Pmax ~550 mW) are successfully fabricated by blade coating under atmospheric condition. The CE approach remarkably improves the device performance by reaching a power conversion efficiency of 18.4% for small area (0.1 cm2), 16.5% on larger area (1 cm2) devices, and 12.7% and 11.6% for blade-coated modules with an active area of 17 and 50 cm2, respectively. Non-encapsulated triple cation solar cells and modules show promising stability under atmospheric shelf life and light soaking conditions.