Solution-Based Electrical P-type Doping of Semiconducting Polymer Films Over a Limited Depth in High-Performance Organic Photovoltaic Devices
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The objective of this research is to explore a simple way of electrically doping organic semiconducting films for applications in high efficiency organic photovoltaic devices. Solution-based electrical doping protocols may allow more versatility in the design of organic electronic devices; yet, controlling the diffusion of dopants in organic semiconductors and their stability has proven challenging. Here a solution-based approach is presented for electrical p-doping of films of donor-like conjugated organic semiconductors and their blends with acceptors over a limited depth with a decay constant of 10-20 nm by post-process immersion into a polyoxometalate solution (phosphomolybdic acid, PMA) in nitromethane. PMA-doped films show increased electrical conductivity and work function, reduced solubility in the processing solvent, and improved photo-oxidation stability in air. This approach is applicable to a variety of organic semiconductors used in photovoltaics and field-effect transistors. PMA doping over a limited depth of bulk heterojunction polymeric films in which amine-containing polymers were mixed in the solution used for film formation enables single-layer organic photovoltaic devices, processed at room temperature, with power conversion efficiencies up to 5.9 ± 0.2% and stable performance on shelf-lifetime studies at 60 °C for at least 280 h.