An investigation into the paintbrush deposition technique for P3HT:PCBM based organic heterojunction solar cells

摘要

Research in organic semiconductor materials and devices has increased dramatically in the last decade, particularly in the photovoltaics field. Organic based solar cells with record power conversion efficiencies of 8% to 9% have recently been reported, and future expectations for organic solar cell power conversion efficiencies are believed to approach 15%. Organic semiconductors hold interest due to their flexible mechanical properties and their ability to be solution processed. Processing techniques such as: spin coating, drop casting, roll painting, and ink jet printing can be readily used to deposit dissolved solutions of polymers and fullerenes to create organic solar cells. One novel, minimally researched solution processing technique for the deposition of polymer and fullerene solutions is paint brushing. Current research on paintbrushed solar cells has shown that solar cell efficiencies close to 5% can be obtained from active layer paint brushing on heated indium-tin-oxide covered glass substrates. In this study, organic solar cells are fabricated from P3HT and PCBM in chlorobenzene solution via paint brushing technique. Unlike previous studies, no heat treatment is applied to P3HT:PCBM active layers during or after device production. Paint-brushed devices are compared to spin-coated devices fabricated from the same P3HT:PCBM chlorobenzene solution in an effort to further investigate why paint-brushed solar cell devices perform better than non-annealed, spin-coated solar cell devices. Results from a full device characterization process including light current-voltage measurements, dark current-voltage measurements, active layer absorbance measurements, and external quantum efficiency measurements for both paint-brushed and spin-coated devices will be shown and discussed. Atomic Force Microscopy is used to provide active layer thickness data and film morphology information for both paint-brushed and spin-coated devices. Practical issues concerning using the paint-brush technique for organic solar cell fabrication are also covered.