Theoretical design and prediction of novel fluorene-based non-fullerene acceptors for environmentally friendly organic solar cell

Abstract

Organic solar cells (OSCs) with electron-withdrawing cyano-group (−C≡N) have created massive interest by exhibiting higher efficiencies. Nevertheless, introducing the − C≡N group through malononitrile during their synthesis is highly toxic and harmful to the environment. Therefore, the development of environmentally friendly OSCs (EFOSCs) is of utmost importance. Taking inspiration from the recent reports, this manuscript looks to suggest more efficient novel fluorene-based EFOSCs based on DTC-T-F type molecule containing fluorene as central core and thiophene as the linker. The − C≡N of 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene) malononitrile (TC) present as an end-capped acceptor in DTC-T-F is replaced with non-toxic electron-pulling units -CF3, -SO3H, –NO2 and a novel series developed through quantum chemical calculation of fluorene-based photovoltaic materials (C1- C9). Frontier molecular orbital, density of state, heat maps of TDM, and finally, the charge shift process is observed by blending the C3 acceptor with donor polymer PTB7-Th (HOMOPTB7-Th-LUMOC3). The designed molecules gave comparable and better results from reference C. The minimum energy gap is observed in C3, C6 and C9 molecules with 2.29 eV, 2.28 eV and 2.27 eV energy gap values respectively. The proposed C9 compound exhibits a prominent redshift in solvent (681.82 nm) and gas phase (618.88 nm). Open circuit voltage (Voc) is the key parameter while assessing the OSC efficiency. The highest Voc is possessed by C5 (2.05 V). Exciton binding energy (Eb) is computed, and C7 has the lowest value of Eb = 0.38 eV. Finally, the reorganization energy values shown by proposed molecules indicate that fluorene-based series are effective candidates for manufacturing EFOSCs. All of the data showed that the designed molecules not only have superior optoelectronic properties to those of the synthetic compound, but also possess environmentally benign properties. This theoretical understanding will provide a CNfree strategy for developing next-generation EFOSCs and novel fluorene-based environmentally friendly materials for OSCs applications.

Keywords

• DFT
• Fluorene
• Non-fullerene acceptors
• Environmental friendly organic solar cells
• Photovoltaic properties