Alkyl Diamine-Induced (100)-Preferred Crystal Orientation for Efficient Pb–Sn Perovskite Solar Cells

The narrow band gap lead–tin (Pb–Sn) perovskite is a promising light absorption layer for highly efficient perovskite solar cells (PSCs), particularly for tandem applications. However, its random crystal orientation dramatically limits its power conversion efficiency (PCE). Here, a propane diamine bromide (PDABr) additive is developed to effectively modulate the Pb–Sn perovskite to grow along the (100)-preferred orientation. It is found that the PDA cations naturally anchor onto the colloidal perovskite nucleus to serve as a surface template to modulate the perovskite crystal to grow preferentially along its (100) orientation, while the bromide ions aid in increasing the grain size, resulting in a densely packed film with significantly reduced density of grain boundaries. As a result, the PDABr-based film exhibits increased carrier mobility and reduced defect density. With these merits, the PDABr-based Pb–Sn PSCs demonstrated an impressive PCE of 20.41%, which is much higher than that of the control device (16.23%). This work provides a general approach to realize the preferred crystal growth for Pb–Sn perovskite films to attain high optoelectronic performance.