Towards sustainable photovoltaics: studies of new absorber materials

Thin film heterojunction solar cells based on chalcopyrites such as CuIn(Ga)Se2 (CIGS) have achieved impressive efficiencies. However concern about the long term sustainability of photovoltaics based on scarce or expensive raw materials has prompted the search for alternative absorber materials. In this work, films of alternative p-type absorber material such as Cu2ZnSnS4 and Cu3BiS3 have been prepared by electrodeposition routes followed by annealing. Two approaches were studied. In the first a metallic precursor (either sequential metal layers or an alloy) were electrodeposited and the layers were then converted to the sulfides by annealing in a sulfur atmosphere. The second approach involved codeposition of the metallic and chalcogen components from non-aqueous solutions. The as-deposited and annealed layers were characterized by photoelectrochemical methods in order to evaluate their potential. The photocurrent measured using a Eu3+ electrolyte contact confirmed that the materials were ptype, and analysis of the photocurrent spectra gave values of the bandgap of the materials that confirm that they are both potential candidates to replace CIGS. The doping density of the films was examined using capacitance measurements with electrolyte and mercury contacts. Preliminary attempts to fabricate solar cells using these new absorber materials will be presented.