Stearic acid as a potential interlayer at the FAPI/hole transport layer interface

Abstract

In this study, we explore the potential of using an ultra-thin film of stearic acid (SA) as an interlayer at the interface between the active material and the hole transport layer (HTL) in perovskite solar cells (PSCs). The FAPbI3 active material thin film was fabricated under ambient conditions using the antisolvent method, followed by the deposition of stearic acid overlayers of varying coverages/thicknesses. By adjusting the coverage/thickness of the SA overlayer, the electronic structure of the perovskite surface can be finely tuned, which may potentially lead to favorable energy level alignment at the perovskite/HTL interface. The interaction between the perovskite thin film and the stearic acid overlayer is expected to involve coordination between defects on the perovskite surface and the carboxyl group of stearic acid. The presence of the nonpolar alkyl chain of stearic acid on the perovskite surface enhances material stability by preventing water and oxygen ingress. Our findings suggest that introduction of SA interlayer at the perovskite/HTL interface may enhance operational stability and efficiency of PSCs by improving the charge transfer across the interface through optimization of energy level alignment and reduction of recombination sites, and protect the absorber from environmental factors like water and oxygen.