Core/CdS quantum dot/shell mesoporous solar cells with improved stability and efficiency using an amorphous TiO₂ coating

Here we present a CdS quantum dot sensitized solar cell based on a mesoporous TiO₂ film with remarkable stability using I ^-/I₃ ^- electrolyte. Chemical Bath Deposition (CBD) was used to deposit the CdS quantumdots within the porous network. We show that a thin coating of the QD sensitized film with an amorphous TiO₂ layer 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 TiO₂ into 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%.