Charge Extraction From TiO2 Nanotubes Sensitized With CdS Quantum Dots by SILAR Method

Quantum dot (QD) solar cells based on different materials have received a noticeable interest during the past ten years; however, their efficiency and stability are still the main drawback of this technology, which leads to a lack of performance of these devices. There are several electron loss (and efficiency) processes involved after photon absorption, but perhaps the main issue is with the electron recombination after excitation of the surface. In this paper, we have studied the dependence of short-circuit photocurrent of TiO2 nanotubes with varying amounts of CdS QDs deposited by the successive ionic layer adsorption and reaction method. We have found that there is an optimum coverage of CdS in order to achieve the maximum photocurrent value. This behavior is explained and characterized in terms of prevailing recombination processes at higher CdS coverage, where quantum confinement becomes less important. By using the charge extraction method, we could determine the time dependence of electrode charge and indicates that the back reaction of electrons with the redox electrolyte present in solution is of the first order in electron density and that it originates from the electrons present in the TiO2 conduction band.