Issue 26, 2019

Tailoring exciton diffusion and domain size in photovoltaic small molecules by annealing

Abstract

Exciton diffusion is an important part of light harvesting in organic photovoltaics (OPVs) because it enables excitons to reach the interface between donor and acceptor and contribute to the photocurrent. Here we used simple and cost-effective techniques of thermal annealing and solvent vapour annealing to increase the exciton diffusion coefficient and exciton diffusion length in two liquid crystalline electron donor materials BQR and BTR. We found that the three-dimensional exciton diffusion length increased to ∼40 nm upon annealing in both materials. Grazing-incidence wide angle X-ray scattering (GIWAXS) measurements show an increase of crystallite size to ∼37 nm in both materials after thermal annealing. We determined an average domain size of these materials in the blends with PC71BM using diffusion-limited fluorescence quenching and found that it increased to 31 nm in BTR PC71BM blends and to 60 nm in BQR PC71BM blends. Our results provide understanding of how annealing improves device efficiency.

Graphical abstract: Tailoring exciton diffusion and domain size in photovoltaic small molecules by annealing

Supplementary files

Article information

Article type
Paper
Submitted
18 fev 2019
Accepted
08 apr 2019
First published
19 apr 2019

J. Mater. Chem. C, 2019,7, 7922-7928

Tailoring exciton diffusion and domain size in photovoltaic small molecules by annealing

M. T. Sajjad, Y. Zhang, P. B. Geraghty, V. D. Mitchell, A. Ruseckas, O. Blaszczyk, D. J. Jones and I. D. W. Samuel, J. Mater. Chem. C, 2019, 7, 7922 DOI: 10.1039/C9TC00951E

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