Systematic variation of the stabilizer to reduce the annealing temperature of sol-gel derived titanium oxide in inverted organic solar cells

Solution-processed titanium oxide is used as an electron selective window layer in inverted organic solar cells. For the goal of roll-to-roll processed organic photovoltaics annealing temperatures of 150 °C and above have to be avoided. Therefore the influence of different stabilizers (complexing agents) on the required annealing temperature for the TiOxTiOx layers is investigated. A clear connection between the boiling points of the different complexing agents and the annealing temperature is observed. In total a series of four different stabilizers with boiling points ranging from 55 °C to 140 °C have been studied. By applying a low boiling complexing agent in the synthesis of the TiOxTiOx-nanoparticles the required annealing temperature could be brought down from 150 °C to 85 °C while maintaining a power conversion efficiency of 3.4% using a mixture of Poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl-C61-butyric acid methyl ester as the photoactive layer.