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• Mandal, Arkalekha; Mohn, Chris Erik; Görbitz, Carl Henrik & Roy, Anurag (2026). Cocrystal Engineering of Organic Semiconductors for Photovoltaic Applications: Modeling Excited-State Properties of a Charge Transfer Cocrystal of a Dicarbazole Donor and a Fluoranil Acceptor. Journal of Physical Chemistry C. ISSN 1932-7447. 130(2), p. 897–897. doi: 10.1021/acs.jpcc.5c06828. Full text in Research Archive Show summary

  With the recent advancements in lightweight, flexible, and environmentally benign organic supramolecular aggregates for various optoelectronic applications, cocrystals of aromatic π-donors and π-acceptors have emerged as promising n-type semiconductors and near-infrared absorbers for enhanced photovoltaic properties. Herein, we demonstrate the electron-dominant charge transport and wide absorption spanning from ultraviolet (UV) to NIR-I region (375–800 nm) of a cocrystal with π-donor 4,4′-bis(carbazol-9-yl)biphenyl (CBP) and π-acceptor 1,4-tetrafluoro-p-benzoquinone (fluoranil) as the components. The crystal packing in CBP:(fluoranil)2 is characterized by mixed stacks of alternative CBP and fluoranil molecules tethered by strong face-to-face π···π stacking interactions. The electron-dominant charge transport in the CBP:(fluoranil)2 cocrystal is governed by the “superexchange” hopping mechanism along the D–A mixed π-stack and is dominated by factors like the energy and symmetry of the frontier molecular orbitals of the CBP and fluoranil moieties. The narrow bandgap (≈1.2 eV) and the high value of the superexchange electron transfer integral (≈100 meV) confirm the potential application of this cocrystal as the active layer material in n-type organic field effect transistors (OFETs). In addition, the strong absorption spanning from the UV to near-infrared region, narrow and direct bandgap, and low exciton binding energy indicate that the CBP:(fluoranil)2 cocrystal can also be exploited for photovoltaic applications. The electron–hole distribution offset, exciton size, and one-electron transition density matrix analyses confirm facile charge transfer exciton generation and dissociation leading to free charge carriers. The calculated value of spectroscopy-limited maximum efficiency (SLME) from periodic density functional theory (DFT) calculations for this cocrystal shows that it can reach a photoconversion efficiency (PCE) of 31%, implying its potential applicability as a practical photovoltaic material.

• Mandal, Arkalekha; Mohn, Chris Erik; Görbitz, Carl Henrik; Rogowska, Melania & Nilsen, Ola (2025). Elucidating the role of charge transfer on semiconductor properties in a new donor–acceptor cocrystal 1,5-dihydroxynaphthalene : TCNQ. Molecular Systems Design & Engineering. 10(7), p. 519–533. doi: 10.1039/d5me00033e. Full text in Research Archive Show summary

  In this work, we have investigated the semiconducting properties of an unprecedented 1 : 1 π-stacked donor–acceptor cocrystal of 1,5-dihydroxynaphthalene (DHN) as the π-donor (D) with 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) as the π-acceptor (A). Molecular semiconductors with electron dominant transport, narrow bandgap, solution processing ability, air-stability are highly sought-after for application in n-channel organic field effect transistors. The DHN : TCNQ cocrystal shows n-type semiconductor nature with a narrow bandgap of around 1 eV, and a low LUMO energy level (−3.8 eV) making it less prone to areal degradation. The electron dominant transport in this cocrystal is described by assuming that electron and hole hop via a super-exchange mechanism along the mixed ⋯D–A⋯ π-stack direction. The participation of bridging molecular orbitals other than donor HOMO make a significant contribution to the super-exchange electron transfer, thus resulting in electron hopping from acceptor to acceptor which is four times larger than the value of hole hopping from donor to donor. Detailed analysis of crystal packing and electronic properties demonstrate that the super-exchange charge carrier transport is facilitated by strong π⋯π stacking interaction between the donor and acceptor, and prominent charge transfer.

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