Electrospray-deposited vanadium oxide anode interlayers for high-efficiency organic solar cells

Spray coating, in competition with conventional spin coating, has attracted extensive attention among large-scale solution casting techniques for producing high-performance organic solar cell (OSC) devices. Solution-processed vanadium oxide (VOx) is used extensively as an anode interlayer (AIL) in OSCs because of its unique optical and electronic properties. In this study, we optimized VOx AILs prepared using electrospray deposition (ESD-VOx) and compared them with AILs prepared using spin coating (SC-VOx); various ESD-VOx properties were found to be optimized at a flow rate of 6.25 μL/min. The OSC active layer used was poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl3- fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-bthiophenediyl): [6,6]phenyl-C71-butyric acid methyl ester (PTB7:PC71BM). The ESD-VOx devices had transmittance and surface morphology comparable to SC-VOx interlayers used in high-efficiency OSC devices. X-ray photoelectron spectroscopy indicated that the obtained ESD-VOx surfaces had a favorable chemical composition. Measurement of hole mobilities using the space charge limited current method showed values of 4.36 × 10−4 and 1.39 × 10−4 cm2 V−1 s−1 for ESD- and SC-VOx, respectively. The charge transport resistance, measured by impedance spectroscopy, was very low for ESD-VOx devices, indicating that there faster charge transportation occurs within these devices because of enhanced hole mobility. These data are consistent with the carrier lifetimes of 1.59 × 10−8 and 4.53 × 10−4 s for ESD- and SC-VOx, respectively. The enhanced charge transportation properties, which can reduce charge recombination, can be attributed to the advantageous surface and interfacial properties of ESD-VOx AILs. Results indicate that optimized ESD had unperturbed diode characteristics with an improved power conversion efficiency, compared to spin coated VOx, of 7.61%.