Determination of Solvent Systems for Blade Coating Thin Film Photovoltaics

With lab-scale solution-processed thin fi lm photovoltaic (TFPV) devices attaining market relevant effi ciencies, 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 fi ve-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% effi ciency, respectively, greater than the effi ciency 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 fi ve-step process results in new nonhalogenated solvent pathways for the scalable deposition of thin fi lm photovoltaic materials.

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