The effect of thickness on the performance of CdSe:Cu2+—quantum dot-sensitized solar cells

The role of the thickness in the counter electrodes is one of the most important criteria for determining the photoelectric conversion efficiency. In this study, we report a novel strategy for optimizing the thickness of CdSe:Cu films in the quantum dot-sensitized solar cells by changing the successive ionic layer absorption and reaction cycles. The result shows that there was a sharp increase in photoelectric conversion efficiency from 1.8 to 4.23% with the SILAR cycles of CdSe:Cu films from 1 to 5 layers due to the effect of CdSe:Cu nanoparticles size on the optical and photovoltaic properties of the devices. In addition, the recombination resistances of the devices can be increased when the SILAR cycles of the counter electrodes changed from 1 layer to 5 layers. To study the above mentioned strategy, the dynamic processes were discussed in detail using the values of the dynamic resistances as: external and internal resistances ( R D , R d ), series resistance ( R S ), shunt resistance ( R SH ) from one illuminated I – V curve and resistance movement of charge at the Cu 2 S/electrolyte and the FTO/TiO 2 interface ( R ct1 ), resistance against the electron diffusion in the TiO 2 and the charge recombination resistance at the TiO 2 /QDs/electrolyte interface ( R ct2 ) from electrochemical impedance spectra.