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"Nanorod metal oxide based electrodes and their application in hybrid photovoltaics."

As a result of quickly increasing energy consumption, together with the need to produce this energy in a clean and sustainable fashion, photovoltaics is attracting abundant interest in the scientific community. Nowadays, the third generation photovoltaics poses a promising approach to further lower the production cost of solar cells. One of the representatives in this breed of photovoltaics is the hybrid solar cell, which is based on the combination of an inorganic and an organic semiconductor. Generally, an n-type inorganic semiconductor acts as the electron acceptor and a p-type semiconducting polymer serves as an light absorber and electron donor. Currently, metal-oxides such as ZnO and TiO2 have attracted a lot of interest for the integration into hybrid solar cells due to their low-cost synthesis, reduced amount of toxicity compared to other inorganic semiconductors, good stability, and convenient electrical and optical properties.

The big challenge remains to control the dimensions and morphology of metal oxides for the development of hybrid solar cells with high performances. To this end, vertically ordered nanorods arrays are a promising solution. Charge transport is highly dependent on the pathway of the charge carriers, so the one-dimensional structure of the nanorods provides a highway for electrons to the electrode. Moreover, this morphology ensures a large interface where electron-hole pairs can be split.

In this PhD-thesis, we demonstrate the latest developments in our research towards application of metal oxides nanorod arrays/polymer for hybrid solar cells. Recently, we published a 40% increase in efficiency and for hydrothermally grown ZnO nanorods combined with poly-(3-hexylthiophene-2,5-diyl) (P3HT) through optimization of the ZnO/polymer interfacial area in combination with appropriate blocking layers for holes and electrons. Further enhancement of the efficiency for this type of solar cells is achieved by controlling the diameter and the packing density of the metal oxide nanorods, which lead to a record efficiency for ZnO nanorods/P3HT hybrid solar cells. Another important highlight, from an environmental point of view, is the possibility of creating a fully water-based hybrid solar cell. This work demonstrates the potential of hybrid photovoltaics and their viability concerning environmentally friendly device processing