Determination of Solvent Systems for Blade Coating Thin Film Photovoltaics

With lab-scale solution-processed thin film photovoltaic (TFPV) devices attaining market relevant efficiencies, the demand for environmentally friendly and scalable deposition techniques is increasing. Replacing toxic halogenated solvents is a priority for the industrialization of solution-processed TFPV. In this work, a generalized five-step process is presented for fabricating high-performance devices from nonhalogenated inks. Resulting from this process, several new solvent systems are introduced based on thiophene, tetralin, 1,2,4-trimethylbenzene, o-xylene, and anisole for blade coating of three different diketopyrrolopyrrole-based (pDPP5T-2, pPDPP5T-2S, and P390) bulk heterojunctions applied in organic photovoltaic devices. Devices based on pDPP5T-2S and P390 attain 5.6% and 6.1% efficiency, respectively, greater than the efficiency either material reached when processed from the halogenated solvent system commonly used. These processes are implemented without post-deposition annealing treatments or additives. The Hansen solubility parameters of the pDPP5T-2 material are obtained, and are used, along with wettability data on a variety of substrates, to determine optimum solvent combinations and ratios for deposition. This generalized five-step process results in new nonhalogenated solvent pathways for the scalable deposition of thin film photovoltaic materials.