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

The fabrication of high quality film with large grains oriented grown along the direction of film thickness is of great importance for the two-dimensional (2D) Ruddlesden-Popper perovskite-based solar cells (PVSCs) with high power conversion efficiency (PCE). In this work, for the first time, we realized the fabrication of high quality 2D BA
₂
MA
_n-1
Pb
_n
I
_3n+1
(BA
⁺
= butylammonium, MA
⁺
= methylammonium, n = 5) perovskite film, with enlarged grain size over 1 μm and preferential orientation growth by introducing a second spacer cation (SSC+) into the precursor solution. As evidenced by dynamic light scattering measurement, SSC+ addition can induce aggregation in the precursor solution. The precursor aggregates are favorable for the formation of large crystal grains via 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 BA
₂
MA
_n-1
Pb
_n
I
_3n+1
(n=5) PVSCs. The unsealed device shows good moisture stability by maintaining around 90% of its initially efficiency after 1000 hours' exposure to the air (Hr = 25±5
^%
). The present work provides a new route toward a highly efficient and stable PVSCs for future commercialization.