Simultaneous modification of interface and modulation of crystal growth by deep eutectic solvent for FACs-Based perovskite solar cells

Improving the interface property and crystallographic orientation of perovskite films has been considered as the bottleneck to improve the optoelectronic performance of perovskite solar cells (PSCs). However, the precise manipulation of preferential crystal orientation by interfacial layers and their underlying impact mechanism on the device performance is still not well understood. In this study, deep eutectic solvent (DES), which is prepared by mixing choline chloride (Chcl) and propanedioic acid (PA) in a molar ratio of 1:1, is employed as a buried interface layer to finely adjust the preferred crystal orientation of the FACs-based perovskite. On the one hand, the DES can modify SnO2, which is conducive to improving electron extraction and transport abilities. On the other hand, the DES can interact with perovskite by forming coordination bonds, electrostatic interactions, and hydrogen bonds, which is beneficial for inducing perovskite crystal orientation along the (1 0 0) crystal plane, causing reduced trap density and hence retarded non-radiative recombination of PSCs. The preferred crystal orientation enhances the quality of the perovskite film. Consequently, a power conversion efficiency (PCE) of 21.11 % is obtained, which is higher than 18.11 % of the pristine PSC. Moreover, the unencapsulated device maintains 87 % of its initial PCE after aging for more than 1100 h in the air. This work presents a feasible method for controlling perovskite orientation growth by interface DES layer.