DFT analysis of different substitutions on optoelectronic properties of carbazole-based small acceptor materials for Organic Photovoltaics

Abstract

In this present study, we have investigated a series of six new novels A-π-D-π-A type small non-fullerene acceptor molecules to enhance the efficiency of organic solar cells. The designed acceptors consist of carbazole moiety as donor (central core) and 3-ethylrhodanine moiety as end-capped acceptor group which is linked via different conjugated π-linkers namely benzo[c][1,2,5]thiadiazole, benzo[c][1,2,5]oxadiazole, thiophene, furan, and [1,2,5]oxadiazolo[3,4-c]pyridine. DFT (HSE06) and TD-DFT (M05) calculations have been carried out with 6-311G(d,p) basis set to investigate the effect of different π-linkers on the charge transfer rate, stability, and optoelectronic properties. Different π-linkers have resulted in smaller HOMO-LUMO energy gap as compared to reference. All investigated molecules M1, M2, M4, M5 and M6 have shown significant bathochromic shift of 31, 12, 92, 78 and 47 nm compared to R except M3 which has shown slightly blue shift of 22 nm, respectively. The reorganization energy analysis predicted the ambipolar behavior of designed molecules. Molecular electrostatic potential maps (MEP), the density of state (DOS), and electron density difference maps (EDDM) analysis have shown the stability parameters and confirmed the higher charge transfer between different fragments within the designed molecules. Thusly, energy level analysis indicates that designed molecules M1, M2, M4 and M5 could act as suitable non-fullerenes acceptors with previously designed PffBT4T-2OD donor for practical solar cells applications.