The Impact of Backbone Fluorination and Side-Chain Position in Thiophene-Benzothiadiazole-Based Hole-Transport Materials on the Performance and Stability of Perovskite Solar Cells.

Perovskite solar cells (PSCs) currently reach high efficiencies, while their insufficient stability remains an obstacle to their technological commercialization. The introduction of hole-transport materials (HTMs) into the device structure is a key approach for enhancing the efficiency and stability of devices. However, currently, the influence of the HTM structure or properties on the characteristics and operational stability of PSCs remains insufficiently studied. Herein, we present four novel push-pull small molecules, H1-4 , with alternating thiophene and benzothiadiazole or fluorine-loaded benzothiadiazole units, which contain branched and linear alkyl chains in the different positions of terminal thiophenes to evaluate the impact of HTM structure on PSC performance. It is demonstrated that minor changes in the structure of HTMs significantly influence their behavior in thin films. In particular, H3 organizes into highly ordered lamellar structures in thin films, which proves to be crucial in boosting the efficiency and stability of PSCs. The presented results shed light on the crucial role of the HTM structure and the morphology of films in the performance of PSCs.