Effect of ZnS coating on the photovoltaic properties of CdSe quantum dot-sensitized solar cells

Abstract

CdSe quantum dots (QDs) were adsorbed onto nanostructured TiO2 films for different times by using a chemical bath deposition method in order to produce QD-sensitized solar cells (QDSSCs). Surface modification was done by coating ZnS onto the CdSe QDs. The optical absorption and current-voltage characteristics of these devices were studied. The size of the CdSe QDs increased with increasing adsorption time, and there was an optimum CdSe adsorption time for achieving the best photovoltaic conversion efficiency. The photovoltaic properties of short-circuit current density, open-circuit voltage, and photovoltaic conversion efficiency were significantly improved after modifying the surface with ZnS. Under a solar illumination of 100 mW/cm2, an efficiency as high as 2.02% was achieved for the CdSe QDSSCs that were made by using this method.

Modeling High-Efficiency Quantum Dot Sensitized Solar Cells

“…In the development of QDSCs two main approximations for the preparation of high harvesting material have been employed: the use of presynthesized colloidal QDs 17,18 and the direct growth of QDs on a TiO 2 surface by chemical bath deposition (CBD) 19,20 or SILAR. 16 Colloidal QDs present good performance but low QD loading and CBD higher loading but can present QD aggregation, 14 which introduces a deleterious effect in cell performance.…”

“…15 QDSCs with different CdSe SILAR cycles were prepared and characterized with JϪV curves (see Figure 1c and Table 1). All the samples were coated with ZnS to reduce the recombination of electrons in the TiO 2 to the polysulfide electrolyte 14,19 with a consequent increase in the photocurrent. On the other hand, Cu 2 O was used as counter-electrode material to enhance the charge transfer between counter-electrode and polysulfide, 18,21 reducing the series resistance of the device and increasing the FF to a value of ϳ0.5 (see Table 1), significantly higher than the reported values of 0.3Ϫ0.4 using Pt or Au as counter-electrodes.…”

“…All the samples analyzed in this study have been coated with ZnS, after SILAR sensitization, by twice dipping alternately into 0.1 M Zn(CH 3 COO) 2 and 0.1 M Na 2 S solutions for 1 min/dip, rinsing with Milli-Q ultrapure water between dips. 19 At least two cells have been prepared at each condition obtaining a variation on cell performance among cells lower than 15%, for cells not presenting problems during the ensemble process (see an example in Supporting Information section S6).…”

“…CdSe QDs have been grown directly on a TiO 2 surface by successive ionic layer adsorption and reaction (SILAR) 16 to ensure high QD loading. ZnS coating 14,18,19 and previous growth of CdS 20 were analyzed. Polysulfide electrolyte 12,20 and Cu 2 S counterelectrodes 18,21 were used to provide higher photocurrents and fill factors, FF.…”

Harnessing Infrared Photons for Photoelectrochemical Hydrogen Generation. A PbS Quantum Dot Based “Quasi-Artificial Leaf”

“…40 Reference "only CdS" samples have been produced, following the same steps described above, except the deposition of PbS.…”