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Here we present a CdS quantum dot sensitized solar cell based on a mesoporous TiO2film with remarkable stability using I−/I3−electrolyte. Chemical Bath Deposition (CBD) was used to deposit the CdS quantum dots within the porous network. We show that a thin coating of the QD sensitized film with an amorphous TiO2layer strongly improves the performance and photostability of the solar cell. We propose that the coating passivates QD surface states which act as hole traps and are responsible for photodegradation of the device. In addition, this coating decreases the recombination of electrons from the CdS quantum dots and the mesoporous TiO2into the electrolyte solution. We obtain a significant improvement of all cell parameters resulting in a total light to electric power conversion efficiency of 1.24%.

The illumination of a dye sensitized solar cell (DSSC) shifts the chemical potential of the electrolyte positively with respect to its dark value. This shift is a result of the charge separation process in which electrons are injected into the TiO2electrode and positive charges are transferred to the electrolyte. In this study, we attempted to measure the electron density in TiO2under operating conditions by monitoring the hole concentration (chemical potential) in the electrolyte solution. However, the results obtained showed that the chemical potential of the electrolyte in DSSCs is not solely determined by the redox concentrations. The charging of the mesoporous medium alters the electrochemical parameters inside the electrode volume. These changes refer to the ionic strength, the ionic activity, or the standard potential. Consequently, we describe a phenomenon to control the electrochemical potential of an electrolyte solution by altering the nanometric pore size of the TiO2matrix. While significant for both the analysis and the design of DSSCs, this new phenomenon opens a path for the manipulation of electrochemical processes utilizing mesoporous electrodes.