Vertical and lateral morphology effects on solar cell performance for a thiophene–quinoxaline copolymer:PC 70BM blend

Hansson, Rickard; Ericsson, Leif K. E.; Holmes, Natalie P.; Rysz, Jakub; Opitz, Andreas; Campoy-Quiles, Mariano; Wang, Ergang; Barr, Matthew G.; Kilcoyne, A. L. David; Zhou, Xiaojing; Dastoor, Paul; Moons, Ellen

doi:10.1039/C5TA00683J

Vertical and lateral morphology effects on solar cell performance for a thiophene–quinoxaline copolymer:PC ₇₀BM blend

Journal Article · Fri Feb 13 00:00:00 EST 2015 · Journal of Materials Chemistry. A

DOI:https://doi.org/10.1039/C5TA00683J· OSTI ID:1214432

Hansson, Rickard ^[1]; Ericsson, Leif K. E. ^[1]; Holmes, Natalie P. ^[2]; Rysz, Jakub ^[3]; Opitz, Andreas ^[4]; Campoy-Quiles, Mariano ^[5]; Wang, Ergang ^[6]; Barr, Matthew G. ^[2]; Kilcoyne, A. L. David ^[7]; Zhou, Xiaojing ^[2]; Dastoor, Paul ^[2]; Moons, Ellen ^[1]

Karlstad Univ., Karlstad (Sweden)
Univ. of Newcastle, Callaghan (Australia)
Jagiellonian Univ., Krakow (Poland)
Humboldt Univ. of Berlin, Berlin (Germany)
Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Bellaterra (Spain)
Chalmers Univ. of Technology, Goteborg (Sweden)
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

The distribution of electron donor and acceptor in the active layer is known to strongly influence the electrical performance of polymer solar cells for most of the high performance polymer:fullerene systems. The formulation of the solution from which the active layer is spincoated plays an important role in the quest for morphology control. We have studied how the choice of solvent and the use of small amounts of a low vapour pressure additive in the coating solution influence the film morphology and the solar cell performance for blends of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and [6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₀BM). We have investigated the lateral morphology using atomic force microscopy (AFM) and scanning transmission X-ray microscopy (STXM), the vertical morphology using dynamic secondary ion mass spectrometry (d-SIMS) and variable-angle spectroscopic ellipsometry (VASE), and the surface composition using near-edge X-ray absorption fine structure (NEXAFS). The lateral phase-separated domains observed in films spincoated from single solvents, increase in size with increasing solvent vapour pressure and decreasing PC₇₀BM solubility, but are not observed when 1-chloronaphthalene (CN) is added. A strongly TQ1-enriched surface layer is formed in all TQ1:PC₇₀BM blend films and rationalized by surface energy differences. The photocurrent and power conversion efficiency strongly increased upon the addition of CN, while the leakage current decreased by one to two orders of magnitude. The higher photocurrent correlates with the finer lateral structure and stronger TQ1-enrichment at the interface with the electron-collecting electrode. This indicates that the charge transport and collection are not hindered by this polymer-enriched surface layer. Neither the open-circuit voltage nor the series resistance of the devices are sensitive to the differences in morphology.

View Accepted Manuscript (DOE)

Research Organization:: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

Grant/Contract Number:: AC02-05CH11231

OSTI ID:: 1214432

Journal Information:: Journal of Materials Chemistry. A, Journal Name: Journal of Materials Chemistry. A Journal Issue: 13 Vol. 3; ISSN JMCAET; ISSN 2050-7488

Publisher:: Royal Society of ChemistryCopyright Statement

Country of Publication:: United States

Language:: English

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