Interface Modification by Metformin Hydrochloride for MA-Free Perovskite Solar Cells

Over the past decade, the efficiency of perovskite solar cells (PSCs) has markedly improved through strategies involving component regulation, controlled crystallization, and interface modification. In this research metformin hydrochloride (MF) was used as a post-treatment agent for MA-free (CsFA) perovskite films to mitigate defect states and enhance device performance. Utilizing dynamic spin coating with varying concentrations of MF, we identified that saturated MF solutions yield optimal results. Specifically, MF elevated the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text{OC}}$</tex> from 1.07 V to 1.12 V and increased device efficiency from 19.38 % to 21.09 %. XRD and SCLC results confirmed that MF effectively passivates surface defects without altering the perovskite crystal structure or morphology. The reduction in defect state density minimizes non-radiative recombination, thereby facilitating a larger quasi-Fermi level splitting and enhancing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text {OC }}$</tex>. These findings demonstrate that MF interface modification strategy is a viable strategy for advancing the efficiency of MA-free PSCs.