Layered organic-inorganic hybrid perovskites have emerged as more intrinsically stable materials for solar cells. While most works employed simple organic cations (such as butylammonium and phenethylammonium), there is an urgent need to go beyond these simple organics to understand how the chemical nature of (complex) organic cations affects the properties of the hybrid perovskites and related devices.
The You group at UNC Chapel Hill has been focusing on the development and understanding of the function of organic cations in these layered organic-inorganic hybrid perovskites, in particular, the structure-property relationships. Depending upon the functions that these organics can offer, we can arbitrarily group these organic cations into three main categories: non-covalent interactions, optoelectronic properties and chirality. For the non-covalent interactions, we found that these weak interactions indeed play important roles in the crystal formation and significantly affect the film properties. As a result, the photovoltaic devices based on these layered perovskites can be greatly improved by tuning the non-covalent interactions, e.g., mono-fluorination of phenethylammonium. We also designed perfluorophenethylammonium and introduced strong aryl-perfluoroaryl interaction to enhance the stability of photovoltaic devices. For optoelectronic properties, we have designed and synthesized conjugated thiophene oligomers for hybrid perovskites. Through collaborations with HYBRID3 teams, crystal structures of different hybrid perovskites have been determined, and interesting fundamental phenomenon (e.g., energy transfer/charge transfer) were discovered and carefully investigated. Finally, we are designing and synthesizing new chiral organic cations to investigate the properties of such chiral molecules based organic-inorganic hybrid perovskites and developing spintronic devices based on these novel materials.