Influence of cysteine adsorption on the performance of CdSe quantum dots sensitized solar cells

The surface of mesoporous TiO2 electrodes has been functionalized with cysteine using different solutions for the subsequent attachment of colloidal CdSe QDs solved in toluene. The adsorption behavior of both cysteine and CdSe QDs on the TiO2 nanoparticles has been investigated by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectroscopy. The photoelectrochemical properties of the CdSe QDs sensitized TiO2 electrode have been characterized by using UV–vis spectroscopy, photocurrent-potential measurement, open-circuit voltage decay, and cyclic voltammetry. It is found that the amount of adsorbed cysteine becomes excessive when highly concentrated aqueous solutions were adopted instead of toluene solutions, leading to a blocking for the diffusion and adsorption of the CdSe QDs. This is translated into a decrease of light harvesting and short circuit current (Jsc) in the solar cell devices. On the other hand, it is suggested that the large amount of adsorbed cysteine on the surface of the TiO2 electrode could reduce the electron recombination at the interface between the TiO2 electrode and the electrolyte. As a consequence, the charge transfer resistance and fill factor became larger, and the electron lifetime became longer.