Stable and Efficient Halide Perovskite Solar Cells by Using Guanidinium-Incorporated Quasi-2D Perovskite Layer

Halide perovskite solar cells are a rising star in the photovoltaic community due to their remarkable performance and rapid progress. Solution processability of hybrid perovskite semiconductors makes these materials especially attractive for low cost and scalable manufacturing. While halide perovskite solar cells already show remarkable improvement with a power conversion efficiency above 25%, poor stability under ambient environmental conditions of heat, humidity, and light is the major issue hindering the commercialization of this technology. Layered two-dimensional (2D) perovskites have been extensively investigated for improving the stability of perovskite solar cells while sacrificing efficiency. In this study, we have explored pathways to improve the stability of perovskite solar cells while maintaining their efficiency by using a 2D perovskite layer. First, halide perovskite solar cells using quasi-2D guanidinium-based halide perovskites synthesized with lead acetate (PbAc) have higher efficiency and stability compared to perovskite solar cells with quasi-2D perovskite synthesized from traditional lead iodide (PbI). This is due to a characteristic perpendicular orientation of the quasi-2D perovskite crystal structure, which can facilitate charge extraction. The power conversion efficiency of quasi-2D perovskite solar cells using PbAc is approximately two times higher than solar cells using PbI. Another intriguing aspect of guanidinium-based quasi-2D perovskite solar cells is a continuous improvement in efficiency that spans several weeks. This observed enhancement is attributed to age-induced recrystallization, showcasing the material's potential for prolonged stability and delay in the onset of device degradation. As a result, the quasi-2D perovskite solar cells maintained almost the same performance even after 3,000 hours. Also, we present an alternative approach that improves the performance of halide perovskite solar cells by introducing an orderly stacking of MAPbI₃ film as a 3D halide perovskite light-harvesting layer on top of a quasi-2D GA₂MA₄Pb₅I₁₆ halide perovskite layer. The power conversion efficiency of quasi-2D/3D perovskite solar cells is approximately 20% higher than that observed for 3D perovskite-based solar cells fabricated under the same conditions. The observed improvement is attributed to the superior crystallinity and excellent film quality achieved by the coherent stacking of 3D MAPbI₃ on top of quasi-2D GA₂MA₄Pb₅I₁₆ perovskites. Additionally, the improved photovoltaic performance of these quasi-2D/3D perovskite solar cells does not compromise their durability. Even after 1,900 hours of storage, the devices maintained about 98% of their initial performance.