Modulation of intermolecular interactions in hole transporting materials for improvement of perovskite solar cell efficiency: a strategy of trifluoromethoxy isomerization

Rational design of hole transport materials (HTMs) can significantly enhance the performance of perovskite solar cells (PSCs). In this work, in order to provide a strategy of molecular design, three HTMs (JY4-JY6) are designed through modulating the intermolecular interactions within carbazole-diphenylamine-based HTMs for enhancing the efficiency of PSCs. On the basis of the DFT, TD-DFT, Marcus theory, and MD simulations, though the designed HTMs exhibit similar electron structures, optical properties and solubility, trifluoromethoxy isomerization in the designed HTMs can yield different intermolecular interactions and surface adsorption on perovskite films. Specifically, the molecule of JY6 demonstrates an inter-molecular co-directional alignment, which can offer an additional C-H/pi stacking pathway for promoting a strong electronic-coupling between the adjacent molecules. Related experiments further confirmed heightened hole mobility, smoother film morphology, enhanced hole extraction and reduced charge recombination at the perovskite/JY6 interface. Therefore, PSC devices based on JY6 achieve a champion PCE of 22.06% compared to the devices based on JY4 (PCE of 18.84%) and JY5 (PCE of 20.94%) under equivalent conditions. Through a combination of theoretical calculations and experimental exploration, we substantiate the feasibility of obtaining potential HTMs via trifluoromethoxy isomerization to modulate the intermolecular interactions for enhancing the efficiency of PSCs. A trifluoromethoxy isomerization strategy to modulate intermolecular interactions is proposed to balance the intermolecular interactions of hole transport materials and their interface interactions with perovskites.