High-Voltage Photogeneration Exclusively via Aggregation-Induced Triplet States in a Heavy-Atom-Free Nonplanar Organic Semiconductor

Nicholas C. Davy, Marius Koch, Guy Olivier Ngongang Ndjawa, Xin Lin, Gabriel J. Man, Yun Hui L. Lin, Jeni C. Sorli, Barry P. Rand, Antoine Kahn, Gregory D. Scholes, Yueh Lin Loo

Research output: Contribution to journalArticle

Abstract

The electron–hole recombination kinetics of organic photovoltaics (OPVs) are known to be sensitive to the relative energies of triplet and charge-transfer (CT) states. Yet, the role of exciton spin in systems having CT states above 1.7 eV—like those in near-ultraviolet-harvesting OPVs—has largely not been investigated. Here, aggregation-induced room-temperature intersystem crossing (ISC) to facilitate exciton harvesting in OPVs having CT states as high as 2.3 eV and open-circuit voltages exceeding 1.6 V is reported. Triplet excimers from energy-band splitting result in ultrafast CT and charge separation with nonradiative energy losses of <250 meV, suggesting that a 0.1 eV driving force is sufficient for charge separation, with entropic gain via CT state delocalization being the main driver for exciton dissociation and generation of free charges. This finding can inform engineering of next-generation active materials and films for near-ultraviolet OPVs with open-circuit voltages exceeding 2 V. Contrary to general belief, this work reveals that exclusive and efficient ISC need not require heavy-atom-containing active materials. Molecular aggregation through thin-film processing provides an alternative route to accessing 100% triplet states on photoexcitation.

Original languageEnglish (US)
Article number1901649
JournalAdvanced Energy Materials
Volume9
Issue number48
DOIs
StatePublished - Dec 1 2019

All Science Journal Classification (ASJC) codes

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

Keywords

  • electro-optical materials
  • intersystem crossing
  • luminescence
  • organic electronics
  • photovoltaic devices
  • solar cells
  • triplet excitons

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