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Kim, Jin Young
Next Generation Energy Laboratory
Research Interests
  • Polymer solar cells, QD solar cells, organic-inorganic hybrid solar cells, perovskite solar cells, OLEDs, PeLEDs, organic FETs

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Effects on Photovoltaic Characteristics by Organic Bilayer- and Bulk-Heterojunctions: Energy Losses, Carrier Recombination and Generation

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Title
Effects on Photovoltaic Characteristics by Organic Bilayer- and Bulk-Heterojunctions: Energy Losses, Carrier Recombination and Generation
Author
Lee, Tack HoPark, Song YiDu, XiaoyanPark, SujungZhang, KaichengLi, NingCho, ShinukBrabec, Christoph J.Kim, Jin Young
Issue Date
2020-12
Publisher
American Chemical Society
Citation
ACS APPLIED MATERIALS & INTERFACES, v.12, no.50, pp.55945 - 55953
Abstract
We investigate the photovoltaic characteristics of organic solar cells (OSCs) for two distinctly different nanostructures, by comparing the charge carrier dynamics for bilayer- and bulk-heterojunction OSCs. Most interestingly, both architectures exhibit fairly similar power conversion efficiencies (PCEs), reflecting a comparable critical domain size for charge generation and charge recombination. Although this is, at first hand, surprising, a detailed analysis points out the similarity between these two concepts. A bulk-heterojunction architecture arranges the charge generating domains in a 3D ensemble across the whole bulk, while bilayer architectures arrange the specific domains on top of each other, rather than sharp bilayers. Specifically, for the polymer PBDB-T-2F, we find that the enhanced charge generation in a bulk composite is partially compensated by reduced recombination in the bilayer architecture, when nonfullerene acceptors (NFAs) are used instead of a fullerene acceptor. Overall, we demonstrate that bilayer-heterojunction OSCs with NFAs can reach competitive PCEs compared to the corresponding bulk-heterojunction OSCs because of reduced nonradiative open-circuit voltage losses, and suppressed trap-assisted recombination, as a result of a vertically separated donor-to-acceptor nanostructure. In contrast, the bilayer-heterojunction OSCs with the fullerene acceptor exhibited poor photovoltaic characteristics compared to the corresponding bulk devices because of highly aggregated acceptor molecules on top of the polymer donor. Although free carrier generation is reduced in a in a bilayer-heterojunction, because of reduced donor/acceptor interfaces and a limited exciton diffusion length, more favorable transport pathways for unipolar charge collection can partially compensate the aforementioned disadvantages. We propose that the unique properties of NFAs may open a technical venue for the bilayer-heterojunction as a great and easy alternative to the bulk heterojunction.
URI
https://scholarworks.unist.ac.kr/handle/201301/50048
URL
https://pubs.acs.org/doi/10.1021/acsami.0c16854
DOI
10.1021/acsami.0c16854
ISSN
1944-8244
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