(Ag_xCu_(1-x))_2ZnSnS_4 THIN-FILMS PREPARED BY SPRAY PYROLYSIS

摘要

One of the most detrimental problems in the further development of thin film solar cells based on kesterite type compound semiconductors is the limitation in open circuit voltage (V_(oc)). The latter, according to many theoretical and experimental studies, is mostly related to the high concentration of intrinsic defects, mainly with Zn_(Cu) antisites. Recently, a way for overcoming this problem by partial substitution of Cu cations by Ag was proposed. This may lead to a strong decrease of intrinsic defects due to higher formation energy of Zn_(Ag) defects and as result to increase of V_(oc). Taking this into account, we performed an investigation of (Ag_xCu_(1-x))_2ZnSnS_4 thin films deposited by the spray pyrolysis method. The as-deposited thin films with 10, 15 and 20% of Ag were annealed at 450°C for 60 min in presence of elemental sulfur. Structural investigations by XRD, as well as Raman spectroscopy studies confirmed the formation of solid solutions. Photoluminescence investigations showed one broad band, which exhibits the blue shift with the increase of Ag concentration. This could be explained by changes in the activation energy of the defect levels involved in radiative transition rather than with the band gap change.