Direct evidence of Z-scheme effect and charge transfer mechanism in titanium oxide and cadmium sulfide heterostructure

Abstract

Although Z-scheme effect plays a significant role in explaining the transfer mechanism of photogenerated electrons and holes between semiconductor heterostructure, the existence of Z-scheme effect can only be proved via limited photocatalytic experimental means as an indirect evidence at present. Our research confirms the direct evidence of Z-scheme effect according to the experimental results from the view of thermodynamics and kinetics, and substantiates the typical competitive relation for transfer of photogenerated electrons and holes between Z-scheme effect and traditional semiconductor heterostructure effect respectively. The surface photovoltage (SPV) spectroscopy, photoacoustic (PA) spectroscopy and transient photovoltage (TPV) are firstly applied in the study of Z-scheme effect between titanium oxide and cadmium sulfide (TiO 2 /CdS) heterostructure. SPV and PA responses are generally acknowledged as classic technologies to analyze the excitation, separation, transfer and recombination properties on photogenerated electrons and holes, and TPV responses are an indispensable method to study the behavior of photogenerated electrons and holes. • The existence of Z-scheme effect is found by SPV spectroscopy, PA spectroscopy and SPV transient. • The competitive relation of charge transfer is confirmed between Z-scheme effect and traditional type II transfer. • The balance of Z-scheme effect is revealed from the view of thermodynamics and kinetics.