Nanoparticle derived Cu(In, Ga)Se2 absorber layer for thin film solar cells

Abstract

A non-vacuum process for fabrication of Cu(In, Ga)Se2 (CIGS) absorber layer from the corresponding nanoparticle precursors was described. CIGS nanoparticle precursors was prepared by a low temperature colloidal route by reacting the starting materials (CuI, InI3, GaI3 and Na2Se) in organic solvents, by which fine CIGS nanoparticles of about 20nm in diameter with chemical composition of Cu0.9In0.64Ga0.23Se2.00 were obtained. The nanoparticle precursors were mixed with organic binder material for the rheology of the mixture to be adjusted for the doctor blade method. After depositing the mixture of CIGS with binder on Mo/glass substrate, the samples were preheated on the hot plate in air to evaporate remaining solvents and to burn the organic binder material. Subsequently, the resultant (porous) CIGS/Mo/glass sample was selenized in a two-zone Rapid Thermal Process (RTP) furnace in order to get a solar cell applicable dense CIGS absorber layer. The selenization at 550°C for 15min with Se gas evaporated at 400°C resulted in the growth of CIGS particles up to a few hundred nanometers in grain size in the upper parts of the layer with remaining unreacted small particles in the lower parts.