Theoretical investigation by DFT and TDDFT the extension of π-conjugation of novel carbazole-based donor materials for bulk heterojunction organic solar cell applications

In this study, we have proposed seven designed symmetrical compounds (C-2-C-8) having a D-pi-A-pi-D structure based on derivative carbazole as a donor by introducing various pi-spacer groups into the reference compound C-1-Ref having a D-A-D structure in order to understand the influence of different pi-spacers on their efficiency in BHJ solar cells. Various parameters such as geometrical structures, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), nonlinear optical properties (NLO), optical properties, light-harvesting efficiency (LHE), reorganization energy, chemical reactivity indices, exciton binding energy (E-b), open-circuit voltage (V-OC), and fill-factor (FF) have been investigated using the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The results show that the extended pi-conjugation of the designed compounds (C-2-C-8) produces a lower energy gap (E-g), a stronger and broader absorption spectrum, lower reorganization energies and exciton binding, and higher nonlinear optical properties compared to C-1-Ref, indicating that these designed compounds are promising as electron donors in BHJ-OSCs. Additionally, the calculated V-oc, FF, and LHE of all compounds showed that the C-2, C-3, C-4, C-5, and C-7 compounds have the best performance in BHJ solar cells compared to the others. In particular, C-4 and C-5 are excellent candidates for the effective donor materials of BHJ solar cells due to their large V-oc, FF, and LHE than the other compounds. This theoretical investigation is expected to provide new strategies to synthesize efficient donor materials for BHJ-OSCs.

Automated summary

In this study, seven designed symmetrical compounds were proposed and analyzed for their performance in BHJ solar cells. The results showed that the designed compounds exhibited superior optical and electrical properties, with C-4 and C-5 compounds performing the best in BHJ solar cells.