Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 40: [CPP] Organic Electronics and Photovoltaics II (Joint Session DS/CPP/HL/O)

O 40.7: Vortrag

Dienstag, 23. März 2010, 15:15–15:30, H37

Influence of injection and extraction barriers realized by choice of donor and HTL on organic solar cell performance — •Wolfgang Tress, Ellen Siebert, Karl Leo, and Moritz Riede — TU Dresden, Institut für Angewandte Photophysik

In the p-i-n solar cell architecture, the active materials of a donor/acceptor flat heterojunction are sandwiched between two doped transport layers, which provide a highly conductive contact to the cathode metal and the ITO, respectively. This concept allows for a systematic study of the influence of the HOMO of the donor and the adjacent hole transport layer (HTL) on the open circuit voltage (V_oc) and the shape of the IV curve. This approach avoids the main problems emerging by metal-organic interfaces like varying work functions, unpredictable interface dipoles, etc.. Additionally, extraction barriers, which cannot be realized by the choice of metal, can be adjusted in a controlled way by a HOMO of the HTL lying deeper than the HOMO of the donor. Using donor and HTL materials with a HOMO between 5.0 and 5.6 eV in combination with C₆₀ as acceptor, we demonstrate a systematic dependence of V_oc on the HOMO of the donor, whereas the built in field is goverened by the HOMO of the strongly doped HTL. The fill factor (FF) is mainly influenced by the HOMO offset between donor and HTL. Both types of barriers (extraction and injection) decrease FF resulting in s-shaped curves with different characteristics. The experimental results are interpreted by comparison to simulation data of a drift-diffusion model, treating the HOMO barrier with a field dependent lowering effect.