2-Fluoroethylamine Hydrochloride Additive for Highly Efficient and Stable FAPbI₃ Perovskite Solar Cells

Adding short-chain methylammonium chloride (MACl) into the precursor solution of formamidine lead iodide (FAPbI3) is a commonly adopted strategy. This addition facilitates the generation of the α-phase and increases the grain size significantly. These changes in turn optimize the light absorption characteristics of perovskite thin films, thereby obtaining a high-quality perovskite thin film with uniform morphology and at the same time enhancing the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, there are few reports of the use of longer alkylammonium chloride salts added to perovskite precursor solutions. Herein, we deliberately elected to introduce 2-fluoroethyl-1-amine hydrochloride (FEACl) into FAPbI3 as an alternative to MACl. The results indicate that FEACl can interact with perovskite precursors; this approach effectively enhances the crystallinity of perovskite thin films while promoting the stabilization of the α-FAPbI3 phase. Moreover, the large cations of FEACl are not incorporated into the lattice, which minimizes the change in the band gap of FAPbI3. The results show that PCE of the optimal device has increased from 23.07% of MACl treatment to 24.30% of FEACl treatment, and the filling factor (FF) has also increased from 81.95 to 84.37%, respectively. When unpackaged devices are stored at room temperature with a relative humidity ranging from 20 to 30% for 1000 h, the PCE is observed to be maintained at 83.57% of its initial value.