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Context <p>We model a library of 36 π-conjugated small molecules of D–A–D and A′–D–A–D–A′ types, combining donor cores (6H-pyrrolo[3,4-b]pyrazine or thieno[3,4-b]pyrazine), central acceptors (benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole) or [1,2,5]thiadiazolo[3,4-g]quinoxaline), and terminal acceptors (benzotriazole, isoindole, phthalimide, benzimidazole) each with or without cyano&#xa0;group. We evaluated frontier orbital energies, open-circuit voltage (<i>V</i><sub><i>oc</i></sub>), fill factor (FF), light-harvesting efficiency (LHE), short-circuit current density (<i>J</i><sub><i>sc</i></sub>), and power conversion efficiency (PCE) for all molecules, and analyzed reorganization energies, transition-density matrix/Hirshfeld descriptors, and charge-transfer parameters for selected cases. Across the library, optical gap ≈0.72–1.96&#xa0;eV, LHE ≈0.32–0.90, FF ≈0.36–0.91, and <i>V</i><sub><i>oc</i></sub> ≈0.06–1.42&#xa0;V. Cyano substitution stabilizes frontier orbital levels. Thieno[3,4-b]pyrazine and especially the [1,2,5]thiadiazolo[3,4-g]quinoxaline core favor higher LHE. Benzotriazole and isoindole terminals fine-tune HOMO/LUMO levels and lower reorganization energies by enhancing planarity. These frameworks consistently deliver top PCE, reflecting the synergy of larger <i>V</i><sub><i>oc</i></sub>, robust LHE, and favorable FF. Across selected compounds, S₁&#xa0;state is predominantly locally excited (LE) with short-range donor-to-acceptor charge transfer, whereas higher singlets often show stronger charge transfer character. Collectively, these trends link donor depth, acceptor electron deficiency, and terminal substitution to key photovoltaic descriptors, providing rational guidelines for designing high-efficiency OPV materials.</p> Method <p>Molecular geometries were optimized and electronic properties calculated using DFT at the B3LYP/6-31G level with Gaussian 16. Excited-state properties were obtained with TD-DFT at the same level of theory. Transition-density matrix, Hirshfeld electron–hole analyses and charge transfer analyses were carried out with Multiwfn 3.8_dev.</p> Graphical Abstract <p></p>

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Density functional modeling of cyano-tuned donor–acceptor molecules for organic photovoltaics

  • 期刊论文

  • 发表日期：

    2025年12月6日

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  • Pinar Seyitdanlioglu

摘要

Context

We model a library of 36 π-conjugated small molecules of D–A–D and A′–D–A–D–A′ types, combining donor cores (6H-pyrrolo[3,4-b]pyrazine or thieno[3,4-b]pyrazine), central acceptors (benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole) or [1,2,5]thiadiazolo[3,4-g]quinoxaline), and terminal acceptors (benzotriazole, isoindole, phthalimide, benzimidazole) each with or without cyano group. We evaluated frontier orbital energies, open-circuit voltage (Voc), fill factor (FF), light-harvesting efficiency (LHE), short-circuit current density (Jsc), and power conversion efficiency (PCE) for all molecules, and analyzed reorganization energies, transition-density matrix/Hirshfeld descriptors, and charge-transfer parameters for selected cases. Across the library, optical gap ≈0.72–1.96 eV, LHE ≈0.32–0.90, FF ≈0.36–0.91, and Voc ≈0.06–1.42 V. Cyano substitution stabilizes frontier orbital levels. Thieno[3,4-b]pyrazine and especially the [1,2,5]thiadiazolo[3,4-g]quinoxaline core favor higher LHE. Benzotriazole and isoindole terminals fine-tune HOMO/LUMO levels and lower reorganization energies by enhancing planarity. These frameworks consistently deliver top PCE, reflecting the synergy of larger Voc, robust LHE, and favorable FF. Across selected compounds, S₁ state is predominantly locally excited (LE) with short-range donor-to-acceptor charge transfer, whereas higher singlets often show stronger charge transfer character. Collectively, these trends link donor depth, acceptor electron deficiency, and terminal substitution to key photovoltaic descriptors, providing rational guidelines for designing high-efficiency OPV materials.

Method

Molecular geometries were optimized and electronic properties calculated using DFT at the B3LYP/6-31G level with Gaussian 16. Excited-state properties were obtained with TD-DFT at the same level of theory. Transition-density matrix, Hirshfeld electron–hole analyses and charge transfer analyses were carried out with Multiwfn 3.8_dev.

Graphical Abstract