Quantum-Confined CdTe Films Deposited by SILAR and Their Photoelectrochemical Stability in the Presence of Se2– as a Hole Scavenger

• Published in: Journal of physical chemistry. C 2014-08, Vol.118 (32), p.18334-18342
• Main Authors: Haydous, Fatima, Halaoui, Lara
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp503971r

Quantum-confined CdTe films were deposited by successive ionic layer adsorption and reaction (SILAR) on nc-TiO2 and on a conducting oxide electrode (FTO) from aqueous solutions of Cd2+ and Te2– prepared in situ under inert atmosphere. The films were characterized with UV–visible absorption, SEM, EDX, and XRD. CdTe n films exhibited a zinc-blende structure and a red-shift in absorbance with increasing SILAR cycles (n) consistent with quantum size effects and featured either a mesoporous morphology on FTO or followed the contours of the titania nanoparticles on nc-TiO2 films. The films’ photoelectrochemical behavior was studied in the presence of Se2– compared to S2– as hole scavengers. The incident-photon-to-current conversion efficiency reached ca. 16% at 460 nm and 9% at 500 nm at CdTe10/nc-TiO2 in alkaline Se2– electrolyte compared to 1% at 460 nm or 0.5% at 500 nm in S2–. CdTe10 films examined after acquiring a photoaction spectrum in Se2– still exhibited zinc-blende structure, EDX analysis showed Cd and Te peaks and no detectable Se, and the absorbance slightly increased with films remaining red-black. On the other hand, the absorbance edge and photocurrent onset shifted significantly to the blue and the films became yellow during the same measurement in S2–, indicating dissolution and formation of CdS, consistent with reports for CdTe single crystals and Q-CdTe. After hours of illumination at 500 nm at −0.55 V in Se2–, Se became incorporated in the films; however, the photocurrent decreased by only 5–8% after 2–3 h illumination, indicating significant photoelectrochemical stability. The results are attributed to effective quenching of the anodic dissolution of CdTe by Se2– scavenging the hole, and a slow growth of a protective overlayer possibly of CdTe1–x Se x that does not block photocurrent generation, in contrast to the behavior of CdTe in sulfide electrolyte.