Influence of Donor Groups on Benzoselenadiazole-Based Dopant-Free Hole Transporting Materials for High Performance Perovskite Solar Cells

The designed hole-transporting materials (HTMs) of asymmetric and symmetric benzoselenadiazole based molecules, referred as RSe-CF, RSe-TPA, and RSe-R, were synthesized and employed for improving the charge conduction and performance of mixed-halide (Cs0.03FA0.97PbI2.9Br0.1) perovskite solar cells (PSCs). In this work, the effects of different acceptor/donor units like 3,5-bis(trifluoromethyl) benzene (CF), alkyl thiophene (R), and triphenylamine (TPA) in benzoselenadiazole were investigated and their optoelectronic, structural, thermal, and photovoltaic properties were studied. The optical and electrochemical results of RSe-CF, RSe-TPA, and RSe-R exhibited the alternation of the energy levels for efficient interfacial charge transfer with mixed-halide Cs0.03FA0.97PbI2.9Br0.1. RSe-TPA HTM-based PSCs displayed the highest power conversion efficiency (PCE) of ∼17.3%, whereas PSCs based on RSe-CF and RSe-R HTMs displayed low PCEs of ∼12.4% and ∼15.9%, respectively. The PCE with a new RSe-TPA HTM is comparable to the PCE of the state-of-the-art HTM Spiro-OMeTAD. Observation of large quenching in photoluminescence spectra of the HTM/Cs0.03FA0.97PbI2.9Br0.1 thin film supported the effective hole injection from perovskite's valence band to HOMO of HTMs, resulting in high PCE and high photocurrent density.