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Influence of Hole‐Transport Layers and Donor Materials on Open‐Circuit Voltage and Shape of I– V Curves of Organic Solar Cells
Author(s) -
Tress Wolfgang,
Leo Karl,
Riede Moritz
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201002669
Subject(s) - organic solar cell , open circuit voltage , heterojunction , materials science , diffusion , polymer solar cell , acceptor , hybrid solar cell , optoelectronics , voltage , solar cell , condensed matter physics , thermodynamics , physics , composite material , polymer , quantum mechanics
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.