Composite Layers for Organic Solar Cells

The donor-acceptor heterojunction is built up from poly(3-(4 -(l ,4 ,7 -triox-aoctyl)phenyl)thiophene) (PEOPT) and C60. The device consisted of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(styrenesulfonate) (PSS) (PEDOT-PSS) layers spin-coated onto an indium tin oxide (ITO)/glass substrate as the hole-collecting electrode, and A1 as the electron-collecting electrode. The PEDOT-PSS layer is used because the injection/collection conditions for electrons/holes are better, and this results in improved current-voltage characteristics for the device. 

A significant improvement was achieved compared to the layered structure when the heterojunction was realized in bulk (involving a large interfacial area) by 

As the molecular-scale heterogeneity of the active layer greatly influences the power conversion efficiency, it is fundamentally important to identify and control the structural and optical properties and their relation to the function of a photovoltaic device. Ellipsometry is especially useful in determining the complex index of refraction and layer thickness, as well as structural details in thin-film geometry [69-72]. This information is needed to calculate the internal optical electric field distribution and the resulting photocurrent action spectra with respect to the efficiency of thin-film devices [66]. 

Although the above blends, when applied in organic photovoltaic devices, are not - strictly-speaking - a mixture of two or more polymers, their characterization by ellipsometry is analogous to that of polymer blend systems, and offers 

As a basic study, modeling of the photocurrent action spectrum in thin-film organic photovoltaic devices vas reported [66] vith the use of complex indices of refraction and layer thickness of the materials determined with SE. 

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