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From generation to collection – impact of deposition temperature on charge carrier dynamics of high-performance vacuum-processed organic solar cells

Richard Adam Pacalaj Orcid Logo, Yifan Dong Orcid Logo, Ivan Ramirez Orcid Logo, Roderick C. I. MacKenzie Orcid Logo, Seyed Mehrdad Hosseini, Eva Bittrich Orcid Logo, Julian Eliah Heger Orcid Logo, Pascal Kaienburg Orcid Logo, Subhrangsu Mukherjee, Jiaying Wu Orcid Logo, Moritz Riede Orcid Logo, Harald Ade, Peter Müller-Buschbaum Orcid Logo, Martin Pfeiffer, James Durrant Orcid Logo

Energy & Environmental Science

Swansea University Author: James Durrant Orcid Logo

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DOI (Published version): 10.1039/d4ee03623a

Abstract

Vacuum-processed organic solar cells (VP-OSCs) possess many advantages for scalability. However, as the academic community focusses on high performing solution-processed OSCs, detailed studies about the relation between morphology and device characteristics in VP-OSCs are rare. Here, we present a st...

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Published in: Energy & Environmental Science
ISSN: 1754-5692 1754-5706
Published: Royal Society of Chemistry 2024
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URI: https://cronfa.swan.ac.uk/Record/cronfa68098
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Abstract: Vacuum-processed organic solar cells (VP-OSCs) possess many advantages for scalability. However, as the academic community focusses on high performing solution-processed OSCs, detailed studies about the relation between morphology and device characteristics in VP-OSCs are rare. Here, we present a study on a model donor/fullerene VP-OSC system deposited at different substrate temperatures. Substrate heating results in increases in current density and fill factor (FF). Changes in morphology are characterised by grazing-incidence wide-angle scattering (GIWAXS) and resonant soft X-ray scattering (RSoXS). The increase in the degree of crystallinity and preferential orientation of the donor molecule in heated samples results in enhanced absorption increasing current density. The exciton and charge separation efficiency were studied by transient absorption and photoluminescence quenching and only showed minor differences. To study the FF differences, charge transport and non-geminate recombination are studied by optoelectronic measurements and device simulations. The charge carrier kinetics are governed by a large density of trap states. While the energetic disorder and non-geminate recombination under open circuit conditions remain largely unchanged, the increased effective mobility and lower transport disorder observed in photocurrent transients explain the increased collection efficiency for heated devices. We relate this to the increased donor phase purity. Our results suggest that charge recombination and transport are governed by different aspects of disorder related to amorphous and crystalline donor phases. Quantitative comparison with high FF solution-processed OSCs reveals that the low mobility limits FF. Finally, drift-diffusion simulations give an outlook for possible performance increases through further optimisation of the deposition control.
College: Faculty of Science and Engineering
Funders: We gratefully acknowledge Heliatek GmbH and in particular Dr Marieta Levichkova for supplying the tested samples and useful discussions. We would further like to thank Dr Tack-Ho Lee for supplying solution processed reference devices and Dr Weidong Xu for help with the collection of the photoluminescence spectra. R. A. P., Y. D. and J. R. D. would further like to acknowledge the financial support from the EPSRC (project ATIP EP/T028513/1 and Plastic Electronics CDT, EP/L016702/1). R. A. P. would further like to acknowledge the Korean NRF GRL project (NRF-2017K1A1A2013153). P. K. acknowledges financial support from the EPSRC (EP/V035770/1) for his Postdoctoral Fellowship and David Clarke Fellowship and further wishes to thank Linacre College for the award of a Junior Research Fellowship. The work at NCSU was supported by the Office of Naval Research (N000142012155 and N000142412104) and Goodnight Foundation Endowment. J. E. H. and P. M.-B. acknowledge funding from Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – EXC 2089/1 – 390776260 (e-conversion) and by the Bavarian State Ministry of Science, Research, and Arts in the context of the Bavarian Collaborative Research Project Solar Technologies Go Hybrid (SolTech). E. B. acknowledges funding by the Saxon State Ministry of Science and Art within the project STEEP UP. The project was selected in the Joint Transnational Call 2022 of M-ERA.NET 3, an EU-funded network of about 49 funding organisations (Horizon 2020 grant agreement no. 958174).

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