Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors

Biwen Li; Petri Murto; Rituparno Chowdhury; Laura Brown; Yutong Han; Giacomo Londi; David Beljonne; Hugo Bronstein; Richard H Friend

doi:10.1038/s41563-025-02362-z

Intrinsic intermolecular photoinduced charge separation in organic radical semiconductors

Nat Mater. 2026 Jan;25(1):100-106. doi: 10.1038/s41563-025-02362-z. Epub 2025 Sep 30.

Authors

Biwen Li¹, Petri Murto^{1

2

3}, Rituparno Chowdhury¹, Laura Brown², Yutong Han⁴, Giacomo Londi⁵, David Beljonne⁶, Hugo Bronstein^{7

8}, Richard H Friend⁹

Affiliations

¹ The Cavendish Laboratory, University of Cambridge, Cambridge, UK.
² Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
³ Department of Chemistry and Materials Science, Aalto University, Espoo, Finland.
⁴ Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK.
⁵ Department of Chemistry and Industrial Chemistry, University of Pisa, Pisa, Italy.
⁶ Laboratory for Chemistry of Novel Materials, University of Mons, Mons, Belgium.
⁷ The Cavendish Laboratory, University of Cambridge, Cambridge, UK. hab60@cam.ac.uk.
⁸ Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK. hab60@cam.ac.uk.
⁹ The Cavendish Laboratory, University of Cambridge, Cambridge, UK. rhf10@cam.ac.uk.

Abstract

Organic radicals based on tris(2,4,6-trichlorophenyl)methyl (TTM) radicals show efficient photoluminescence from excitons in the spin-doublet manifold, but their potential in charge photogeneration remains unexplored. Here we report that when TTMs are in contact, photoexcitation generates TTM anion-TTM cation pairs. These can decay radiatively or be fully separated under an electric field bias. We use a triphenyl-substituted TTM (P₃TTM) in which the phenyl end groups enhance intermolecular interactions. In dilute (5 wt%) films in a wide-energy-gap organic semiconductor host, we observe prompt photoluminescence from the excited radical at 645 nm, and a delayed component, beyond 1 μs, at 800 nm due to recombination of P₃TTM anion-cation pairs. Measurements of photocurrent made with diode structures with 100% P₃TTM showed close-to-unity charge collection efficiency in reverse bias. We have found 'homojunction' intermolecular charge separation, made possible when the extra energy for double occupancy of the non-bonding radical level on the anion is lower than the energy of the doublet exciton. This opens possibilities for light harvesting using single-material molecular semiconductors.