Thin film photoelectrodes of ternary chalcogenide CdSe1-xTexfor photoelectrochemical solar cells applications

Abstract

The basic requirements of a good thin film photoelectrode for high efficiency photoelectrochemical (PEC) cells are low resistivity and large grain size. The large size grains lead to a reduction of the grain boundary area of the thin films, with important consequences for efficient energy conversion. The low resistivity of the photoelectrodes is required to minimize the series resistance of the PEC cell which leads to lower short circuit current. In addition, we have to tailor the band gap of the material further by adjusting the composition x in the alloy CdSe 1-x Te x . Low resistivity in the materials can be achieved by a careful control of the stoichiometry of the material or by doping with a proper trivalent dopant such as Ga or In. The control of the stoichiometry and the dopant concentration can be achieved by a careful control of the rate/s of deposition/s. The deposition rates should also be kept comparatively low and also the substrates should be heated to elevated temperatures so that the films formed consist of large size grains. It is advisable to also change the angle of deposition from normal incidence to an inclined deposition so that the films will tend to grow with columnar grains, which are very essential. The grain size can be further increased to some extent by carefully annealing the films in vacuum at pre-determined temperature and for a time interval. The large grain size films formed this way should be coated with very thin layers of oxides like TiO 2 or In 2 O 3 to prevent corrosion of the thin film electrodes when used in the PEC cells. Thus, by carefully controlling the various parameters as outlined above, it is possible to obtain high efficiency photo-electrochemical solar cells using these Cd-Se-Te ternary alloy thin films as photoelectrodes.