Multilayer organic photovoltaic devices fabricated by electrospray deposition technique and the role of the interlayer

Multilayer organic photovoltaic (OPV) devices were fabricated using the electrospray deposition method. The film-formation conditions and particularly the solvent composition were investigated to reveal the importance of the boiling point and polarity of the component solvents. The deposited film must be semi-wet to form a flat film by slow-drying at ambient conditions, resulting from the high boiling point and high affinity of o-dichlorobenzene for poly(3-hexylthiophene) (P3HT) and [6,6]-C70-butyric acid methyl ester (PC70BM). On the other hand, a polar solvent assists in the formation of an electrospray with a wide spray range under an applied voltage. Employing the film formation conditions, double-layered (P3HT and PC70BM) and triple-layered (P3HT, interlayer, and PC70BM) OPV devices were fabricated. A diketopyrrolopyrrole derivative, which is a near-infrared-absorbing ambipolar semiconductor, was applied as the interlayer material. By comparing the two devices, it was determined that the interlayer acts as a sensitizer at around 700 nm for the P3HT-PC70BM system.