Probing dark exciton diffusion using photovoltage

Tyler K. Mullenbach, Ian J. Curtin, Tao Zhang, Russell J. Holmes

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

The migration of weakly and non-luminescent (dark) excitons remains an understudied subset of exciton dynamics in molecular thin films. Inaccessible via photoluminescence, these states are often probed using photocurrent methods that require efficient charge collection. Here we probe exciton harvesting in both luminescent and dark materials using a photovoltage-based technique. Transient photovoltage permits a real-time measurement of the number of charges in an organic photovoltaic cell, while avoiding non-geminate recombination losses. The extracted exciton diffusion lengths are found to be similar to those determined using photocurrent. For the luminescent material boron subphthalocyanine chloride, the photovoltage determined diffusion length is less than that extracted from photoluminescence. This indicates that while photovoltage circumvents non-geminate losses, geminate recombination at the donor-acceptor interface remains the primary recombination pathway. Photovoltage thus offers a general approach for extracting a device-relevant diffusion length, while also providing insight in to the dominant carrier recombination pathways.

Original languageEnglish (US)
Article number14215
JournalNature communications
Volume8
DOIs
StatePublished - Jan 27 2017

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (NSF) under CBET-1067681 and DMR-1307066. I.J.C. acknowledges support from the Robert and Beverly Sundahl Fellowship.

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