A strategy to enhance VOC of π-conjugated molecules based on thieno[2,3-b] indole for applications in bulk heterojunction organic solar cells using DFT, TD-DFT, and 3D-QSPR modeling studies

Seven novel organic compounds BHJ-i (i = 1–7) based on carrying 8-alkyl-8H-thieno [2,3-b] indole as a donor, thiophene as a bridge and different acceptors were used for bulk heterojunction organic solar cells (BHJ). The main objective of this work was to find a better acceptor for π-conjugated molecules used in photovoltaic solar cells in order to improve their efficiency. The study was through DFT and TD-DFT quantum methods. Several optoelectronic properties of these materials, electronic properties (EHOMO, ELUMO, and Egap), natural bond orbital (NBO) analysis, quantum chemical parameters (chemical hardness (η), chemical potential (μ) and electronegativity (χ)), UV-vis spectra and the open-circuit photovoltage (Voc), were calculated. We also developed the 3D-QSPR model based on CoMFA and CoMSIA approaches to predict the most important three-dimensional properties of the structure of 8-butyl-8H-thieno [2,3-b] indol-2-yl) thiophen-2-yl) methylene derivatives, which allowed us to design new molecules and optimize their properties for a high-performance Voc. The results indicated that the molecules in this work exhibit a theoretical power conversion efficiency of 7%. Finally, due to 3D-QSPR results, we have designed 10 new molecules, which have very interesting Voc values.