Elucidation of the role of guanidinium incorporation in single-crystalline MAPbI3 perovskite on ion migration and activation energy

Abstract

Ion migration plays a significant role in the overall stability and power conversion efficiency of perovskite solar cells (PSCs). This process was found to be influenced by the compositional engineering of the A-site cation in the perovskite crystal structure. However, the effect of partial A-site cation substitution in a methylammonium lead iodide (MAPbI₃) perovskite on the ion migration process and its activation energy is not fully understood. Here we study the effect of a guanidinium (GUA) cation on the ion transport dynamics in the single crystalline GUA_xMA_1-xPbI₃ perovskite composition using temperature-dependent electrochemical impedance spectroscopy (EIS). We find that the small substitution of MA with GUA decreases the activation energy for iodide ion migration in comparison to pristine MAPbI₃. The presence of a large GUA cation in the 3D perovskite structure induces lattice enlargement, which perturbs the atomic interactions within the perovskite lattice. Consequently, the GUA_xMA_1-xPbI₃ crystal exhibits a higher degree of hysteresis during current-voltage (J-V) measurements than the single-crystalline MAPbI₃ counterpart. Our results provide the fundamental understanding of hysteresis, which is commonly observed in GUA-based PSCs and a general protocol for in-depth electrical characterization of perovskite single crystals.