Influence of hole-transport layers and donor materials on open-circuit voltage and shape of I-V curves of organic solar cells

Journal article

The effect of injection and extraction barriers on flat heterojunction (FHJ) and bulk heterojunction (BHJ) organic solar cells is analyzed. The barriers are realized by a combination of p-type materials with HOMOs varying between -5.0 and -5.6 eV as hole-transport layer (HTL) and as donor in vacuum-evaporated multilayer p-i-metal small-molecule solar cells. The HTL/donor interface can be seen as a model for the influence of contacts in organic solar cells in general. Using drift-diffusion simulations we are well able to reproduce and explain the experimental I-V curves qualitatively. In FHJ solar cells the open-circuit voltage (V_OC) is determined by the donor and is independent of the HTL. In BHJ solar cells, however, V_OC decreases if injection barriers are present. This different behavior is caused by a blocking of the charge carriers at a spatially localized donor/acceptor heterojunction, which is only present in the FHJ solar cells. The forward current is dominated by the choice of HTL. An energy mismatch in the HOMOs leads to kinks in the I-V curves in the cases for which V_OC is independent of the HTL. Copyright © 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

Authors: Tress, W; Leo, K; Riede, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Wiley
• Journal: Advanced Functional Materials
• Volume: 21
• Issue: 11
• Pages: 2140-2149
• Publication date: 2011-06-07
• DOI: 10.1002/adfm.201002669
• EISSN: 1616-3028
• ISSN: 1616-301X
• Language: English
• Keywords: modeling; heterojunctions; organic solar cells; S-kink; charge transport