Interfacial layer formations between Cu(In,Ga)Se2 and InxSy layers -: art. no. 123512

Cu(In,Ga)Se-2 (CIGS) thin-film solar cells with InxSy buffer layers deposited by physical vapor deposition yield efficiencies of up to 14.8%. For substrate temperatures during the InxSy deposition ranging from 23 to 200 degrees C, air annealing of the completed solar cells leads to an improvement of the photovoltaic performance. However, at substrate temperatures of 300 degrees C, the efficiencies are practically zero, and air annealing does not improve this value. To understand the effects of substrate temperature and air annealing on the CIGS/InxSy interfaces of the solar cells, these interfaces have been studied by means of bright-field and high-resolution transmission electron microscopy, selected-area electron diffraction (SAED), and energy-dispersive x-ray spectrometry (EDX). It is shown that air annealing leads to a substantial Cu depletion on the CIGS side of the CIGS/InxSy interface, probably inducing the formation of a compositionally graded interface between the buffer and CIGS. For the 300 degrees C sample, CuIn5S8 formed instead of InxSy, as identified by means of SAED and EDX. The large density of vacancies and defects in the spinel-type cubic crystal structure of CuIn5S8 provides a large number of recombination centers at the heterojunction of the solar cell, thus deteriorating considerably its photovoltaic performance. (c) 2005 American Institute of Physics.