Expanding the photoresponse range of TiO2 nanotube arrays by CdS/CdSe/ZnS quantum dots co-modification

Highly ordered TiO2 nanotube arrays modified by CdS, CdSe and ZnS quantum dots (QDs) were fabricated by using chemical bath deposition. The CdS and CdSe QDs modification expands the photoresponse range of TiO2 nanotube arrays from ultraviolet region to visible range. It is demonstrated that sequentially assembled CdS and CdSe QDs significantly improved the light harvesting ability and photocurrent efficiency, and a high incident photon to current conversion efficiency (IPCE) of 53% was obtained. Further coating the TiO2/CdS/CdSe nanotube array with a barrier layer of ZnS QD increases the IPCE to 72%. The improved photo harvest efficiency of the CdS/CdSe/ZnS co-modified TiO2 arrays is attributed to the formation of an ideal cascade-type energy band structure, which is advantageous for both electron injection and hole recovery.