The great challenge of the 21st century will be the generation of cheap energy for the increasing demand for power. Solar energy is a promising candidate for renewable power production. In the last years the interest in organic photovoltaics grew rapidly, because plastic solar cells have the potential for cheap mass production. There are different crucial starting points to improve the efficiency of this new generation of photovoltaics. The author of this book, Sebastian Mhlbach, focuses on the morphology of the organic layers - one of the most important elements of this type of solar cells. Different methods are used to change this parameter and thus to improve the efficiency.