A wide range of characterization techniques are used to study spin-coated films of zinc oxide (ZnO) obtained from thermal decomposition of zinc acetylacetonate hydrate. Inverted organic solar cells with ZnO transport layers were prepared. Deposition conditions of the solution onto the substrate (e.g. substrate temperature) were found to be crucial in order to obtain well-performing inverted cells. Interestingly, it is demonstrated that full conversion of the precursor into crystalline ZnO is not necessary to prepare well-operating cells.