Formation of Quasi-2D Perovskites using In Situ Multimodal Spin Coater with Grazing Incidence X-Ray Scattering

Hybrid perovskites are a class of ideal absorbing materials for solar cells that suffer from moisture and temperature instability. Single junction PVs using the hybrid perovskites MAPbI₃ and FAPbI₃ (MA= H₃CNH₃, FA= NH₂CHNH₂) have achieved a certified power conversion efficiency (PCE) over 25%, which is very close to the premier silicon PVs. To combat the instability of hybrid perovskites, 2D perovskites that feature large organic ligands that replace MA⁺ or FA⁺ in the 3D structure. Introducing electronically insulating moieties into perovskites makes crystal orientation critical to device efficiency. Nucleation and crystallization mechanisms for large organic ligands remains unknown and can be investigated thoroughly by in situ GIWAXS/SAXS and are vital to the development of stable perovskite solar cells.<br/><br/>The exploration of incorporating ligands into 2D perovskites is allows another tunability parameter to control the mechanical and optoelectronic properties of perovskite materials. While incorporating organic ligands improves moisture stability, it also introduces electronically inactive components, making crystal orientation critical to photovoltaic power conversion efficiency. There have been several efforts to vertically align 2D perovskites by changing thermodynamic procedure conditions, precursor concentration, and precursor type. While there have been efforts to characterize the crystallization dynamics with the 3D perovskites (e.g.MAPbI₃), the dynamics of 2D crystallization are not well understood. To study the formation of quasi-2D films, we have fabricated a custom-made in situ multimodal spin coater system with an integrated heating stage that can be programmed with spinning and heating recipes and coupled with synchrotron-based grazing-incidence WAXS and SAXS (GI-WAXS/GI-SAXS).<br/><br/>Studying the crystallization of quasi-2D perovskite films using synchrotron radiation allows for reduced exposure times, ensuring high time-resolution data that is paired with in situ photoluminescence to understand how the choice of ligand affects film crystallization kinetics, crystallinity, and orientation – all of which are crucial to increasing efficiency. Using the new stage, we have studied the formation of various bithiophene-based (2T) organic ligands at a variety of n-numbers (3, 5, and 10) and compared them to the well-established butylammonium (BA) ligand. In addition, the new stage allows us to control the temperature of the substrate, allowing for the elucidation of how thermal effects can be used to leverage the formation kinetics, thus paving the way for more stable, high efficiency perovskite solar cell materials.