Study of the stability of quantum dot sensitized solar cells

Quantum dot sensitized solar cells have been constructed using photoanodes bearing nanocrystalline titania and CdS, CdSe and ZnS quantum dots. The combined CdSe/CdS system provides enhanced photon absorption in a large range of the visible spectrum, while ZnS plays a passivation and stabilization role. This was verified by micro-Raman scattering studies as a function of light soaking of successively sensitized photoanodes. Annealing of photoanodes resulted in increasing quantum dot size as verified by both UV-vis diffuse reflectance and Raman spectroscopy. It was also found that a composite CdSxSe1-x species was formed at the interface of CdS and CdSe layer, which constitutes a stabilization factor and is further stabilized by annealing, that influences the electric characteristics of the sensitized photoanodes. Single CdS sensitizers, when annealed gave increased photocurrents but suffered a fast decay. Annealing of fully sensitized photoanodes gave a diverse behavior, markedly stabilizing photocurrents under N-2 atmosphere. All cells worked well by using a Pt-free cathode made by chemically growing Cu2S on a brass foil. The employed innovative cell structure provided liberty in designing and optimizing the device geometry. (C) 2013 Elsevier B.V. All rights reserved.