Effect of energy level matching on the enhancement of photovoltaic response about oxide/Zn2SnO4 composites

Abstract

Four oxide/Zn2SnO4 composites (WO3/Zn2SnO4, TiO2/Zn2SnO4, α-Fe2O3/Zn2SnO4 and SnO2/Zn2SnO4) were synthesized via a sol–gel route with the molar ratio 4 : 1 of (W, Ti, Fe and Sn)/Zn. All composites present similar absorption characteristics to their one component (oxide or Zn2SnO4). The surface photovoltage spectroscopies for composites show stronger photovoltaic effects than each component before compounding under zero and the same positive bias. We also find that the separation efficiency of photogenerated charges will increase by degrees with decreasing the difference of conduction band edges between two components under the same conditions. These results are attributed to the energy level matching, and we adopt the overlapping of wave functions to explain the micro-process and physical mechanism of the separation of photogenerated charges in the composite system.