Systematic Modeling of N-Type D-A-D Conjugated Small Molecule-Based Nonfullerene Acceptors for Organic Photovoltaics

This study investigates the impact of six novel (SPZ1-SPZ6) small molecular conjugated nonfullerene acceptors (NFAs), for organic solar cells (OSCs). The designed NFAs are characterized by various advanced quantum chemical simulations of density functional theory (DFT) and time-dependent (TD-DFT) approaches. We revealed in-depth information regarding molecules' structural-property relationship charge transfer and optical absorption characteristics of designed molecules and compared them with synthetic reference molecules (R). The designed SPZ1-SPZ6 molecules exhibit red-shifted absorption, reduced bandgaps and increased extinction coefficients, indicating improved molecular phase separation during thin-film deposition during device fabrication. Moreover, the modeled SPZ1-SPZ6 molecules significantly enhance photophysical, optoelectronic and photovoltaic parameters compared to R. Among these, the designed small molecule SPZ2 exhibits superior UV-Vis absorption of 730.44 nm, surpassing R and others. SPZ2 features the smallest bandgap (2.00 eV) and has a substantial improvement over R's 2.37 eV, and this is due to our efficient molecular modeling strategy. Further investigation revealed efficient charge transfer between the SPZ2 acceptor molecule and PTB7-Th donor molecule complex, making this design capable of producing efficient OSCs in the future.