The Second Spacer Cation Assisted Growth of a 2D Perovskite Film with Oriented Large Grain for Highly Efficient and Stable Solar Cells

The fabrication of high‐quality film with large grains oriented along the direction of film thickness is important for 2D Ruddlesden–Popper perovskite‐based solar cells (PVSCs). High‐quality 2D BA2MAn−1PbnI3n+1 (BA+=butylammonium, MA+=methylammonium, n=5) perovskite films were fabricated with a grain size of over 1 μm and preferential orientation growth by introducing a second spacer cation (SSC+) into the precursor solution. Dynamic light scattering showed that SSC+ addition can induce aggregation in the precursor solution. The precursor aggregates are favorable for the formation of large crystal grains by inducing nucleation and decreasing the nucleation sites. Applying phenylethylammonium as SSC+, the optimized inverted planar PVSCs presented a maximum PCE of 14.09 %, which is the highest value of the 2D BA2MAn−1PbnI3n+1 (n=5) PVSCs. The unsealed device shows good moisture stability by maintaining around 90 % of its initially efficiency after 1000 h exposure to air (Hr=25±5 %). Hochwertiger 2D‐Perowskitfilm: Der Zusatz von Phenylethylammoniumiodid (PEAI) zu einer Vorstufenlösung kann deren Aggregation induzieren. Die Vorstufenaggregate begünstigen die Bildung von orientierten Ruddlesden‐Popper‐Perowskit‐Filmen mit erhöhten Korngrößen >1 mm. Der Wirkungsgrad der Solarzellen steigt drastisch von 2.32 % (0 PEAI) auf 14.09 % (0.1 PEAI).