Optoelectronic Properties of a Simple Metal-Free Organic Sensitizer with Different Spacer Groups: Quantum Chemical Assessments

The optimized geometries, electronic structures, absorption spectra and non-linear optical (NLO) properties of five donor-π-spacer-acceptor (D-π-A)-based organic molecules, namely indolocarbazole-3,4-ethylenedioxythiophene, indolocarbazole-benzothiadiazole, indolocarbazole-furan, indolocarbazole-quinoxaline and indolocarbazole-benzoxadiazole (ICZS1–ICZS5), are analyzed using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The performance of three functionals, Becke’s three parameter Lee–Yang–Parr (B3LYP), Coulomb-attenuating method-B3LYP (CAM-B3LYP) and Grimme’s D2 dispersion model (WB97XD), were analyzed for indolo[3,2,1-jk]carbazole (IC-2). The computed results indicated that absorption spectra of WB97XD are closest to IC-2. As a result, the WB97XD functional was chosen for further studies of ICZS1–ICZS5 dyes. The designed molecules also show excellent performance in terms of smaller energy gap, chemical hardness, red-shifted longer wavelength, free energy change for electron injection, dye regeneration and NLO properties. The results reveal that different spacer derivatives resulted in better performance for the photovoltaic (PV) and NLO properties. In particular, ICZS2 and ICZS5 molecules produced excellent performance of the dye-sensitized solar cells (DSSCs) and NLO properties. Based on the theoretical results, the electronic structures and absorption spectra could be used for rational sensitizer design of organic dyes for optoelectronic applications.