Measurements of dark triplet exciton diffusion in a phosphor-sensitized organic photovoltaic cell

Kaicheng Shi, Ian J. Curtin, Andrew T. Healy, Tao Zhang, David A. Blank, Russell J. Holmes

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Organic photovoltaic cell performance is limited in part by a short exciton diffusion length (LD). While state-of-the-art devices address this challenge using a morphology-optimized bulk heterojunction (BHJ), longer LD would relax domainsize constraints and enable higher efficiency in simple bilayer architectures. One approach to increase LD is to exploit long-lived triplet excitons in fluorescent materials. Though these states do not absorb light, they can be populated using a host-guest triplet-sensitized architecture. Photogenerated host singlets undergo energy transfer to a guest, which rapidly forms triplets that are transferred back to the long-lived host triplet state. Previous efforts have been focused on Pt-and Irbased guests. Here, a host-guest pairing of metal-free phthalocyanine (H2Pc) and copper phthalocyanine (CuPc) is explored, advantageous as the guest also has strong and complementary optical absorption. In optimized devices (20 vol.% CuPc), the short-circuit current is enhanced by 20%. To probe the origin of the enhancement, the exciton LD is measured using a device-based methodology that relies on fitting ratios of donor-to-acceptor internal quantum efficiency as a function of layer thickness. Compared with the neat H2Pc, the LD of the 20 vol.% CuPc doped layer increases from (8.5 ± 0.4) nm to (13.4 ± 1.6 nm), confirming the increased device current comes from enhanced exciton harvesting.

Original languageEnglish (US)
Title of host publicationOrganic, Hybrid, and Perovskite Photovoltaics XX
EditorsZakya H. Kafafi, Paul A. Lane, Kwanghee Lee
ISBN (Electronic)9781510628816
StatePublished - 2019
EventOrganic, Hybrid, and Perovskite Photovoltaics XX 2019 - San Diego, United States
Duration: Aug 12 2019Aug 15 2019

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceOrganic, Hybrid, and Perovskite Photovoltaics XX 2019
Country/TerritoryUnited States
CitySan Diego

Bibliographical note

Funding Information:
The authors acknowledge the financial support by National Science Foundation (NSF) Solid-State and Materials Chemistry DMR-1708177.

Funding Information:
support by National Science Foundation (NSF)

Publisher Copyright:
© 2019 SPIE.


  • Exciton Diffusion Length
  • Organic Photovoltaic Cells
  • Triplet Excitons
  • Triplet Sensitizers


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