Enhanced photovoltaic performance in MA-free triple-cation-based perovskite solar cells with guanidinium modification

Hybrid halide perovskite (HHP)-based solar cells have revolutionized the photovoltaic landscape with their exceptional photovoltaic performance and potential as a low-cost solar technology. Herein, we demonstrate the use of guanidinium cation (GA⁺) as a dopant to tailor the properties of the mixed cation perovskite, formamidinium–cesium lead triiodide (FA_0.83Cs_0.17PbI₃), for improved photovoltaic performance in perovskite solar cells (PSCs). X-ray diffraction (XRD) results reveal that the GA content plays a pivotal role in the formation of α and δ phases in the resultant perovskite structure. Our results indicate that the low/high concentration of GA improves/diminishes device performance. The champion PSC device demonstrates an incredible power conversion efficiency (PCE) of 20.7% and an impressive open-circuit voltage (V_oc) of 1.12 V under one sun illumination and an optimal content of 3% GA⁺ dopant, which is remarkable for an MA-free device. Furthermore, the GA-incorporated perovskite films show much improved moisture and thermal stabilities and increased carrier lifetimes compared with FA–Cs counterparts. This work underscores the potential of GA-doped FA–Cs perovskites in the development of high-performance, stable, and MA-free PSCs, paving the way for their applications in commercial photovoltaic technologies.