Coupled DFT and SCAPS-1D investigation of a novel small-molecule for organic solar cells

Herein, we theoretically developed and studied a novel small-molecule donor, SA1, a phenazine-based derivative, for organic solar cells (OSCs). Density functional theory (DFT) analysis was performed to optimize its electronic and molecular characteristics, which were then employed as input parameters for solar cell capacitance simulator (SCAPS-1D) calculations to explore the photovoltaic properties of the OSC. The SA1 structure incorporated a thieno[3,2-b]thiophene bonded with thioxothiazolidin-4-one as an electron-rich part to improve the lowest unoccupied molecular orbital (LUMO) level, while a dibenzo[a,c]phenazine core operated as a weak electron-acceptor part to enhance the highest occupied molecular orbital (HOMO) level. The influences of different layer parameters, such as thickness, doping level, bulk defect density, and density of states, were systematically studied. The effects of fundamental merits, such as electrode work function, parasitic resistances, and temperature, on OSC efficiency were also discussed. After optimization, our OSC device demonstrated a remarkable power conversion efficiency (PCE) of 16.94%, a fill factor (FF) of 87.34%, an open-circuit voltage (V _OC) of 1.27 V, and a short-circuit current (J _SC) of 15.26 mA cm^-2. Additionally, the designed SA1-based cell showed predictable high thermal stability at 145 °C based on simulation results, along with a high external quantum efficiency (EQE) of 95% in the visible spectrum.