Anode Engineering of Highly Efficient Polymer Solar Cells Using Treated ITO

ITO substrates were treated with organic solvent cleaning(OSC), SC1 treatment[V(NH4OH):V(H2O2): V(H2O)=1:1:5], O-2 plasma and UV ozone, respectively. Combined investigations of atom force microscopy(AFM), water contact angle measurements, ultraviolet photoemission spectroscopy(UPS) and X-ray photoemission spectroscopy(XPS) demonstrated that UV ozone treatment could give rise to the smoothest surface, the most hydrophilic property and the highest work function(WF) of ITO due to the removal of hydrophobic C-O impurity from the ITO surface and the enrichments of more oxygen on the ITO surface. When PEDOT:PSS film[(poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)] was deposited on the ITO substrates treated with UV ozone, it showed a lower root-mean-square roughness in AFM images, a higher transmission in UV-Vis transmission spectra and a higher WF in UPS spectra than the PEDOT:PSS films deposited on the ITO substrates treated by other three methods. As a result, the power conversion efficiency of polymer solar cells(PSCs) based on PTB7:PC71BM as an active layer and ITO treated by UV ozone as an anode can reach 8.48% because of the simultaneously improved short circuit current, open circuit voltage and fill factor compared to the PSCs with ITO treated with other three methods.