Modified processing conditions for optimized organic solar cells with inkjet printed P3HT:PC61BM active layers

Inkjet printing can be used to deposit the functional layers of organic solar cells and it offers advantages over spin coating such as the possibility to print films with user-defined patterns. In this study, inkjet printing was utilized to deposit polymer:fullerene solar cell active layers and different drying and annealing conditions were examined in order to optimize device performance. Low fill factors of approximately 30% were found for devices with printed active layers that were dried at 100 °C and a considerable shift in the fill factor of up to 60% was seen after post-annealing at 150 °C. Changes in the fill factor corresponded to an increase in device efficiency from ∼1.3% to ∼2.4% after post-annealing. An alternative active layer drying procedure was used based on solvent annealing which resulted in high fill factors of 60% and efficiencies of ∼2.4% without post-annealing. Blend films were examined with atomic force microscopy, ultra-violet visible spectroscopy and X-ray photoelectron spectroscopy. It was determined that solvent annealed, inkjet printed active layers are considerably rougher and show enhanced organization with respect to films that were dried at 100 °C. Two preparation routes are provided for devices with printed active layers with acceptable efficiencies based on quick drying and post-annealing or slow drying (solvent annealing).