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

doi:10.1117/12.2528883

10 October 2019 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

Proceedings Volume 11094, Organic, Hybrid, and Perovskite Photovoltaics XX; 110941Q (2019) https://doi.org/10.1117/12.2528883
Event: SPIE Organic Photonics + Electronics, 2019, San Diego, California, United States

Abstract

Organic photovoltaic cell performance is limited in part by a short exciton diffusion length (L_D). While state-of-the-art devices address this challenge using a morphology-optimized bulk heterojunction (BHJ), longer L_D would relax domainsize constraints and enable higher efficiency in simple bilayer architectures. One approach to increase L_D 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 L_D 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 L_D 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.

Citation Download Citation

Kaicheng Shi, Ian J. Curtin, Andrew T. Healy, Tao Zhang, David A. Blank, and Russell J. Holmes "Measurements of dark triplet exciton diffusion in a phosphor-sensitized organic photovoltaic cell", Proc. SPIE 11094, Organic, Hybrid, and Perovskite Photovoltaics XX, 110941Q (10 October 2019); https://doi.org/10.1117/12.2528883

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KEYWORDS

Excitons

Diffusion

Internal quantum efficiency

External quantum efficiency

Absorption

Organic photovoltaics

Optical pumping

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