Wide band gap semiconductors are important due to their optical response at ultraviolet wavelengths. ZnO with a nominal band gap at 3.37 eV is one of them. Specially prepared ZnO surfaces alter significantly the mechanical thermal and optical properties. These newly developed surfaces offer possibilities in a cross disciplinary variety of applications ranging from photovoltaic elements to bio-active materials.
In order to understand a variety of properties of such materials one needs to investigate the primary processes that occur following their excitation. A variety of intrinsic and extrinsic defects (impurities, vacancies and others) introduce a high degree of complexity in the ultrafast electronic and lattice interactions. These ultrafast properties are investigated by using pump-probe experiments . It was found that electron scattering and trapping occurs more efficiently to the nanostructured surface than on a flat ZnO film. This is attributed to the defects and imperfections that are introduced by the micro-conical shape and the nanometer-sized roughness.
In continuing experiments we investigate the influence of the characteristics of nanostructured hybrid (organic-inorganic) solar cells on their photovoltaic response and long term performance. The photoresponse mechanism is based on the ultrafast photogeneration, dissociation and recombination of excitons as well as transport of the generated charge towards the electrodes. The effect of the composition of the material as well as the structural/morphological characteristics of the photoactive layer and the overall architecture on the above mechanisms is being investigated.
 E. Magoulakis, E. L. Papadopoulou, E. Stratakis, C. Fotakis, and P. A. Loukakos, Appl. Phys. A 98 701 (2010).