Asymmetric Fluorinated Cyclopenta[2,1-b:3,4-b']Dithiophene-Based Hole-Transporting Materials for Perovskite Solar Cell

A series of asymmetric hole-transporting materials (HTMs) based on cyclopenta[2,1-b;3,4-b’]dithiophene cores tethered with p-methoxytriphenylamines donor units with or without incorporated fluorine atoms were rationally designed, synthesized, and employed in perovskite solar cells (PSCs). A comprehensive comparison is conducted encompassing the absorption spectra, electrochemical characteristics, thermal stability, density functional theory (DFT) calculations, hole mobility, and surface morphology, as revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), steady-state and time-resolved photoluminescence measurements, water contact angle analyzes, and photovoltaic parameters of the PSCs. The fluorinated HTMs, P-oF and P-mF, demonstrated enhanced hole mobility and more efficient charge extraction at the perovskite/HTM interface compared to their non-fluorinated counterpart. Consequently, PSCs employing P-oF and P-mF achieved power conversion efficiencies (PCEs) of 21.52% and 19.78%, respectively, with negligible hysteresis, outperforming devices based on P-H, which exhibited a PCE of 17.05%. Moreover, the operational stability of the device incorporating P-series as the HTM exceeded that of the PSCs employing the benchmark material of spiro-OMeTAD. The findings presented herein underscore the facile accessibility and potential of asymmetric compounds as alternative HTMs for PSCs. The results provide valuable insights and serve as a reference for the development of optimal HTMs for PSCs.