Amino acid functionalised perylene bisimides for aqueous solution-deposited electron transporting interlayers in organic photovoltaic devices

Abstract

Solution-processable organic solar cells have the potential to offer a low-cost renewable energy source with low energy intensive processing. However, the range of materials that are compatible for forming multilayer photovoltaic devices beyond a bulk heterojunction layer is limited due to a requirement for orthogonal processing to avoid dissolution of layers. Improving charge transport is a key challenge in the pursuit of high efficiency organic photovoltaics. Therefore, the development of solution-processable electron transport layers that are suitable for orthogonal processing is important for the feasibility of solution-processed devices. Here, we present a series of amino acid appended perylene bisimides (PBIs) which have been used as electron transporting interlayers in P3HT/PC₆₁BM based organic photovoltaic cells. These PBIs are easily soluble in water at high pH, allowing for easy solution processability. Despite minimal changes in molecular structure in the series of PBIs, there are profound differences in performance of the solar cells, with the phenylalanine derivative showing the most promising performance. The absorbance, morphology and photoconductivity properties of the PBIs have a strong influence on the suitability of the material as an effective interlayer.