Regensburg 2013 – scientific programme

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O: Fachverband Oberflächenphysik

O 84: Photovoltaics (jointly with CPP, DS and HL)

O 84.7: Talk

Friday, March 15, 2013, 10:45–11:00, H2

The role of defects in nanocrystalline zinc oxide interlayers for polymer-based solar cells — •Sebastian Wilken, Dorothea Scheunemann, Florian Witt, Jürgen Parisi, and Holger Borchert — University of Oldenburg, Department of Physics, Energy and Semiconductor Research Laboratory, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany

In polymer-based bulk heterojunction solar cells, the absorber blend has intrinsically no preferential transport direction for photogenerated charge carriers due to the statistical intermixing of both the donor and acceptor phase. Therefore, additional charge-selective interfacial layers, which are semipermeable membranes for either electrons or holes in an ideal case, are widely used in order to achieve efficient charge extraction at the respective contacts. One well established material for electron collection is zinc oxide (ZnO), which can be processed at moderate temperatures and deposited via solution-based techniques in form of colloidal nanocrystals (NCs). Here, we discuss the influence of defect states in interlayers made of ZnO NCs on the overall solar cell performance. For that purpose, ZnO NCs with different surface-to-volume ratios were wet-chemically synthesized and introduced into indium tin oxide-free polymer solar cells in the inverted device architecture. As indicated by photoluminescence, we show that surface defects play a more and more dominant role with decreasing NC size and, thus, limit the photovoltaic efficiency. For a more detailed analysis of the involved defect states, photo-induced current transient spectroscopy (PICTS) was performed for devices with varying amount of surface defects.