New Routes to Sustainable Materials for Photovoltaic Cells

Due to the availability and low cost of the elements, the semiconductor systems Cu-Sb-Bi-S(e) and Cu-Zn-Sn-S(e) are being studied as sustainable alternatives to the expensive absorber material based on CuIn(Ga)S(e)2. The research is focussed on two main areas: 1) Acquisition of the basic information of the ideal compounds by growth of single crystals of the solid solutions Cu2ZnSnSxSe(4-x) and CuBixSb(1-x)S2 via Chemical Vapour Transport technique. 2) Deposition of thin films of the materials by means of a variety of electrochemical techniques such as one-step electrodepositions from non aqueous solutions containing the metal precursors and elemental S, and electroplating/evaporation routes followed by annealing in S/Se rich environments. The characterization of the properties of both single crystals and thin films of the new materials by a range of structural, electrical and photoelectrochemical techniques are being performed in order to establish their suitability as absorber layer materials for solar energy conversion. Photoactive compounds have been synthesised, with band-gap energy matching the Shockley-Queisser requirements for the efficient harvesting of solar spectrum. Further studies are now carried out in order to improve the photon to current efficiency of these materials.