ZnO nanorod/CdS nanocrystal core/shell-type heterostructures for solar cell applications

Abstract

ZnO/CdS core/shell nanorod arrays were fabricated by a two-step method. Single-crystalline ZnO nanorod arrays were first electrochemically grown on SnO(2):F (FTO) glass substrates. Then, CdS nanocrystals were deposited onto the ZnO nanorods, using the successive ion layer adsorption and reaction (SILAR) technique, to form core/shell nanocable architectures. Structural, morphological and optical properties of the nanorod heterojunctions were investigated. The results indicate that CdS single-crystalline domains with a mean diameter of about 7 nm are uniformly and conformally covered on the surface of the single-crystalline ZnO nanorods. ZnO absorption with a bandgap energy value of 3.30 ± 0.02 eV is present in all optical transmittance spectra. Another absorption edge close to 500 nm corresponding to CdS with bandgap energy values between 2.43 and 2.59 eV is observed. The dispersion in this value may originate in quantum confinement inside the nanocrystalline material. The appearance of both edges corresponds with the separation of ZnO and CdS phases and reveals the absorption increase due to CdS sensitizer. The photovoltaic performance of the resulting ZnO/CdS core/shell nanorod arrays has been investigated as solar cell photoanodes in a photoelectrochemical cell under white illumination. In comparison with bare ZnO nanorod arrays, a 13-fold enhancement in photoactivity was observed using the ZnO/CdS coaxial heterostructures.

Optical absorption enhancement in sensitized ZnO nanorods for solar cells

“…In the first stage ZnO NR were grown on a fluorine doped tin oxide (FTO)-glass substrate by potentiostatic electrodeposition in a three-electrode cell [6][7][8]. The sensitization stage used the previously deposited ZnO NR as a substrate for the deposition of CdS and CdTe.…”

“…The sensitizer used will be determinant in the posterior optical performance of the material; here the most important candidates are CdS or CdTe [4,5]. Previously reported ZnO/CdS NR core-shell array sensitized by Successive Ion Layer Adsorption Reaction (SILAR) shown an increased absorption in the visible [6][7][8]. Moreover, a dependence in the absorption edge position was observed for these samples with the NP size and CdS content in the samples [6][7][8].…”

“…Previously reported ZnO/CdS NR core-shell array sensitized by Successive Ion Layer Adsorption Reaction (SILAR) shown an increased absorption in the visible [6][7][8]. Moreover, a dependence in the absorption edge position was observed for these samples with the NP size and CdS content in the samples [6][7][8]. CdTe is an II-VI semiconductor alloy with a BE between 1.47-1.53 eV [9][10][11][12][13] very close to the optimal BE for photovoltaic applications.…”

“…It is focused on the visible absorption enhancement due to the sensitizations and shows how the CdTe sensitized samples present a red-shift in the BE as was observed in CdS sensitizer ones [6][7][8].…”

The Effect of a Sputtered Al-Doped ZnO Seed Layer on the Morphological, Structural and Optical Properties of Electrochemically Grown ZnO Nanorod Arrays

“…3,[21][22][23][24][25] Among these methods, the electrochemical deposition (ED) method has many advantages such as low growth temperature, simple and low cost process without the need for vacuum systems for preparing ZnO nanorods with high crystalline quality, well suited for scale-up and good electrical contact between structures and substrate. [22][23][24][25][26][27] Several studies of electrodeposition of ZnO NRAs have been reported in the literature. These studies showed the influence of deposition parameters such as growth temperature, zinc precursor concentration, pH, electrodeposition potential and growth time on controlling nanowire morphology, in particular the nanowire diameter and length (i.e.…”