Novel Synthesis Of Vanadium Oxide Thin Films And Their Use In Polymer Solar Cells

Vanadium oxide(VOx)is particularly promising because of its low-cost,high ambient stability,nice optical and electrical properties.Meanwhile,VOx exhibits advantages of a wide range of energy level alignments,good transparency as thin films,easy to control,and low-resistance ohmic contacts for the polymer solar cells(PSCs).Most importantly,as transition metal oxides,one of the most attractive features of VOx is the possibility to be deposited by low temperature solution processing methods.Different methods to prepare VOx have different chemical compositions.As a result,it exhibits different optical and electrical properties,which has very important research value and significance.We demonstrate a facile and green approach to prepare a vanadium oxide hydrate(VOx·nH2O)layer to serve as the hole transport layer(HTL)in high-performance PSCs.The VOx·nH2O layer was in-situ prepared by a combined H2O2 and ultraviolet-ozone(UVO)processing on a VOx layer.The as-prepared VOx·nH2O layer exhibited a work function of ca.5.0 eV,high transmittance and better interfacial property compared to the generally prepared VOx(UVO or thermal annealing)layers.PSCs based on poly [(ethylhexyl-thiophenyl)-benzodithiophene-(ethylhexyl)-thienothiophene]:[6,6]-phenylC71-butyric acid methyl ester(PTB7-th:PC71BM)using the VOx·nH2O layer as HTL yielded high power conversion efficiency(PCE)up to 8.11%,outperforming the devices with the VOx layers(PCE of 6.79% or 6.10% for UVO or thermal annealed VOx layer)and conventional PEDOT-PSS layer(PCE of 7.67%).The improved PCE was attributed to the enhanced JSC and/or FF,which mainly correlates to the improved interfacial contact between the ITO/HTL and active layer when using the VOx·n H2 O layer as HTL.Similar improvement in PCE was also observed for the PSCs based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester(P3HT:PC61BM).In addition,PSCs with a VOx·nH2O layer as HTL showed higher stability than those with a PEDOT:PSS layer.Hence,this simply and in-situ prepared VOx·nH2O layer might be a promising HTL for low-cost and high-performance PSCs.