All-small-molecule organic solar cells with high fill factor and enhanced open-circuit voltage with 18.25 % PCE: Physical insights from quantum chemical calculations

All-small-molecule acceptors (ASMAs) are considered as well-defined molecular structures with good sustainability and processability. Although these acceptor molecules did not exhibit high power conversion efficiency (PCE) as compared to polymer solar cells, a lot of research is yet to be focused on the development of ASMAs. In this report, a new series of ASMAs (ZMY1 to ZMY5) has been designed by end-capped alteration of recently synthesized ZR-Si4 molecule (PCE = 10.10%). Photovoltaic, optoelectronic and geometric parameters of the newly designed molecules have been investigated through DFT and TD-DFT approaches. Additionally, power conversion efficiency along with fill factor (FF) percentage has been computed for the designed molecules. Enhanced open circuit voltage (V_oc) allows PCE at around 18.25 % which is better than the experimentally synthesized ZR-Si4 molecule. Additionally, the high mobility of electrons and hole between metal electrodes also suggested that the designed molecules are effective candidates for the development of efficient organic solar cell (OSC) applications.