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

Lee TH, Park SY, Du X, Park S, Zhang K, Li N, Cho S, Brabec C, Kim JY (2020)

Publication Type: Journal article

Publication year: 2020

Journal

DOI: 10.1021/acsami.0c16854

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.

Authors with CRIS profile

Involved external institutions

Ulsan National Institute of Science and Technology (UNIST) / 울산과학기술원 Korea, Republic of (KR) University of Ulsan / 울산대학교 Korea, Republic of (KR)

How to cite

APA:

Lee, T.H., Park, S.Y., Du, X., Park, S., Zhang, K., Li, N.,... Kim, J.Y. (2020). Effects on Photovoltaic Characteristics by Organic Bilayer- And Bulk-Heterojunctions: Energy Losses, Carrier Recombination and Generation. ACS Applied Materials and Interfaces. https://dx.doi.org/10.1021/acsami.0c16854

MLA:

Lee, Tack Ho, et al. "Effects on Photovoltaic Characteristics by Organic Bilayer- And Bulk-Heterojunctions: Energy Losses, Carrier Recombination and Generation." ACS Applied Materials and Interfaces (2020).

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