Solar cell fill factors: General graph and empirical expressions

In this study, we present the design of five new hole-transporting materials (ZM1, ZM2, ZM3, ZM4, and ZM5) based on dimethylfluorene through end-capped acceptors via thiophene linkers. We aimed to enhance the photovoltaic properties of hole-transporting materials (HTMs) for potential use in high-efficiency perovskite solar cells (PSCs). We employed density functional theory (DFT) based calculations to investigate the electronic and photovoltaic properties of the designed HTMs. Our results demonstrated that designed HTMs possess superior planarity, deeper HOMOs energies, and high solubility with small energy band gap (Eg) compared to the reference (ZR) and Spiro-OMeTAD HTMs, leading hole extraction and efficacious solution processing properties. This effectively drives the transport of holes from the perovskite layer with high open-circuit voltages (1.15 V to 1.25 V). The results of the hole charge transfer integral of the designed HTMs (0.244 eV to 0.346 eV) indicate their improved hole mobility rate for PSCs. Additionally, all designed HTMs exhibited superior anticipated power conversion efficiency (25.87% to 28.33%) with a higher fill factor (0.8948 to 0.9014) compared to the reference molecule (13.22%). Our findings suggested that ZM1-ZM5 molecules are advantageous HTMs for the fabrication of high-performance PSCs, which may have the potential for future commercial use in the solar industry.