A SAMs layer of 3-PPA with a phosphonic acid headgroup and carboxylic acid tailgroups has been used to modify the surface of ZnO nanorods photoanode in CdS quantum dots sensitized solar cells. Its effects on the photovoltic performance have been investigated in detail by adjusting the concentration and deposition time of 3-PPA. Especially, we utilize ultraviolet photoelectron spectroscopy to characterize the variation of band alignment after introducing 3-PPA layer in the solar cells. The results reveal that the 3-PPA not only suppress the electron-hole recombination process due to its passivation on the surface defects, but forms an energy barrier to efficiently retard the back transfer of electrons, which finally results in the enhancement of conversion efficiency of solar cells. (C) 2014 Elsevier B.V. All rights reserved.