However, few attention has been taken on strategy by employing both of above mentioned concepts to facilitate charge carries transportation and minimize recombination simultaneously since such attractive core-shell nanowire structures have been employed in DSSCs [
36,
37]. Recently, TiO
2 nanotubes with a ZnO (Zinc oxide) thin energy gradient has been used in quantum dot solar cells for improved charge-collecting efficiency and reduced recombination [
38]. It should be noted that the introduced ZnO film is subjected to photo-corrosion in aqueous electrolyte with the UV light irradiation [
39]. Only few inorganic materials, such as TiO
2, SrTiO
3, and SnO
2 (Tin oxide) are stable enough to be used as practical solar energy conversion devices,which do not subject to decomposition upon irradiation when used as photoelectrodes in aqueous media [
40]. Based on the consideration for possible practical application, we have developed a hydrothermal method to obtain TiO
2-SrTiO
3 heterostructure nanotube array electrodes with tunable morphology, composition and phtoelectrochemical properties (Scheme 1) [
41]. Well dispersed SrTiO
3 nanocrystallites on TiO
2 nanotube arrays could improve the overall photoelectrochemical performance due to the charge separation within the heterostructures. We speculated that such heterostructures should have excellent ability as the scaffolds for light absorbent in photoelectrochemical solar cells, which has been preliminarily investigated in our recent communication [
42]. In this article, we will give systemic results on such TiO
2-SrTiO
3 heterostructure arrays with different structure as conducting scaffolds in a photoelectrochemical solar cell, in which CdS quantum dot chosen as a demonstration is deposited by a traditional chemical precipitation technique referred to as an successive ionic layer adsorption and reaction (SILAR) [
15,
16,
42,
43] (Scheme 1). By combining the properties of exciton generation in CdS quantum dots, the facilitated charge capture and transport characteristics of TiO
2 nanotube arrays also with the reduced charge recombination process by energy gradient, we have succeeded in developing an effective strategy for harvesting solar energy through CdS-TiO
2-SrTiO
3 composites. Photochemical processes that follow the excitation of CdS QDs, as probed by transient absorption and photoelectrochemical measurements, are presented.