On the Exciton Blocking Layer at the Interface Organic/Cathode in Multiheterojunction Organic Solar Cells

A successful approach to improve organic photovoltaic cell performance is the introduction of a thin layer called the electron-blocking layer (EBL) at the interface organic material/cathode. Here, the effect of the EBL is discussed through the use of different multiheterojunction organic solar cells configurations. It is shown that, whatever the configuration used, classical or inverted cells, the EBL allows to significantly improve the solar cells performances. The optimum thickness of this layer is, whatever the solar cell configuration, 8-9 nm. Both cell families permit achieving high short circuit current through this quite thick insulating layer. This invalidates the justification, proposed in the case of classical solar cells, based on Al diffusion into the exciton-blocking layer, since there is no metal deposition onto the exciton blocking layer in the case of inverted structure. Different hypothesis explaining the high electron current through the 8-9 nm of the large band gap EBL are proposed.