Band alignment tuned by 3-PPA SAMs interfacial modification to enhance the conversion efficiency of ZnO/ZnS heterostructure quantum dots sensitized solar cells

The 3-Phosphonopropionic acid (3-PPA) self-assembled monolayers with a phosphonic acid headgroup and carboxylic acid tailgroups were introduced into the interface of ZnO/ZnS heterostructure by a simple chemical immersion process. Ultraviolet photoemission spectroscopy (UPS) was utilized to determine the variation of band alignment. The UPS results revealed that the 3-PPA can act as buffer layer in ZnO/ZnS heterostructure to lower the energy barrier formed by ZnS. This new energy barrier can not only work efficiently on retarding the back transfer of electrons, but also weaken the blocking effect on the charge injection process, which finally results in the enhancement of photoelectric conversion efficiency.