Heterojunction Engineering of CdTe and CdSe Quantum Dots on TiO₂ Nanotube Arrays: Intricate Effects of Size‐Dependency and Interfacial Contact on Photoconversion Efficiencies

Abstract

The quality of heterojunctions at the quantum dot (QD)‐TiO2 nanotube (TNT) interface has important implications on the efficiencies of photoelectrochemical solar cells. Here, it is shown that electrophoretic deposition of pre‐synthesized thioacid‐capped CdTe QDs results in relatively poor charge transfer across the heterojunctions. This is likely due to the intermediate layer of bifunctional linkers (S‐R‐COOH) in between the QDs and TNT. On the other hand, CdTe QD‐sensitized TNT prepared by in situ deposition in aqueous medium provides direct QD‐TNT contact, and hence more favorable heterojunction for charge transfer. This is exemplified not only by the drastic improvement in photocurrent efficiencies, but also provides clear difference on the size‐dependent electron injection efficiencies from the CdTe QDs of different sizes. By extending the system further to CdSe QDs, drastic enhancement is found when carrying out the in situ deposition in an organic medium. The results are discussed in terms of the nature of deposition and the corresponding charge transport characteristics. More importantly, the work reflects the intricacy of the effects of QD size and the quality of the heterojunctions on the overall photoconversion efficiencies.

Constructing ternary CdS/reduced graphene oxide/TiO 2 nanotube arrays hybrids for enhanced visible-light-driven photoelectrochemical and photocatalytic activity

“…Recently, coupling of the anodized TNTs with narrow band gap semiconductors, such as CdS [13][14][15][16], CdSe [17][18][19], and PbS [20][21][22], have been utilized to improve the photoresponse of TNTs in the visible light region. Under visible light irradiation, these narrow band gap semiconductors can act as sensitizers and facilitate the photoexcited electrons flow from their CB to the CB of TNTs due to that the CB of these semiconductors is higher than that of TNTs, therefore assisting charge separation and improving visible-light-driven PC activity of the TNTs based nanocomposites.…”

Thin ZnO nanocrystalline films for efficient quasi-solid state electrolyte quantum dot sensitized solar cells

“…Recent developments in the field showed that semiconductor quantum dots (QDs) could effectively sensitize wide band gap metal oxides instead of organic dyes [12]. Semiconductor QDs in the form of very small crystals could be very stable while present the advantage to match solar spectrum better because their absorption spectrum can be tailored by size quantization [13,14]. Moreover, the possibility of generation of multiple electronehole pairs from one photon could lead to very high theoretical efficiencies exceeding 66% [15].…”

Efficiency enhancement of CuInS2 quantum dot sensitized TiO2 photo-anodes for solar cell applications

“…Recently, the semiconductor quantum dots (QDs), such as CdS, CdSe, CdTe, PbS, etc. have been employed as a sensitizer to fabricate the high efficient quantum dot sensitized solar cells (QDSSCs) due to their large absorption edge, high extinction coefficients, ultrafast electron transfer, quantum size effect and multiple electron-hole pairs generation [3][4][5][6][7][8][9]. Furthermore, the ternary chalcopyrite with their low toxicity and excellent optical properties has been attracted significant attention in photovoltaic devices [10].…”