Enhancement of the performance of organic solar cells by electrospray deposition with optimal solvent system

Electrospray (ES) as a thin film deposition method that is uniquely suited for manufacturing organic photovoltaic cells (OPVs) with desired characteristics of atmospheric pressure fabrication, roll-to-roll compatibility, less material loss, and possible self-organized nanostructures. The additional solvent with high electrical conductivity plays an important role in ES deposition process to fabricate OPVs with active layer composed of polymer mixture poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PC ₆₁BM). Here we introduced acetic acid, which possesses high electrical conductivity, as additive solvent in ES process. The dependence of device performance on the concentration of acetic acid was investigated, and optimal ratio was obtained. To further demonstrate the influence of additive solvents with different electrical conductivity, OPV devices with active layer deposited by ES method using solutions containing acetic acid, acetone or acetonitrile were fabricated. The characteristics of active layers were revealed by optical microscope, atomic force microscopy, UV-vis spectroscopy and X-ray diffraction. Compared with additive solvents of acetone and acetonitrile, the active layer formed by electrospraying solvent containing acetic acid demonstrated enhanced vertical segregation distribution and improved P3HT crystallinity, which resulted in better device performance. OPV device using acetic acid as additive achieved power convention efficiency (PCE) of 2.99±0.08% under AM 1.5 solar simulation, which is on par with that of the spin coated device (PCE 3.12±0.07%).