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Jitendra Kumar1 Sarang Ingole1

1, Indian Institute of Technology Kanpur, Kanpur, , India

Silver (Ag) has been incorporated at the copper sub-lattice sites in the quaternary compound Cu2ZnSnS4 (CZTS) which is being under intense investigation as an absorber material for the photovoltaic application. Thin films of the resulting pentanary compound (AgxCu1-x)2ZnSnS4 (0 ≤ x ≤ 1) show remarkable changes in their microstructure and electronic properties. With the increasing Ag content, the grain size increased from 0.13 to 2 µm which could be attributed to the liquid assisted grain growth mechanism. While the observed increase in the optical band gap from 1.5 to 2.0 eV could be attributed to the influence of d-orbitals of Ag atoms on the valence band edge of the CZTS compound. The charge carrier density decreased by two orders of magnitude with only 4 atomic % Ag (x = 0.04) incorporated in the films which indicate the strong influence of AgCu on the density of CuZn and VCu point defects which are the major acceptors in CZTS. The reduction of these intrinsic point defects is also being reflected in the observed decrease in the Urbach energy from 336 meV (for x = 0.00) to 230 meV (for x = 0.21). This has been further correlated with the ordering-disordering detected by the near-resonant Raman scattering. These observed changes with increasing Ag content could possibly be used for tailoring the properties of CZTS for the better performance of CZTS based photovoltaics.

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