Ag-doped CuGaSe2 as a precursor for thin film solar cells

For the preparation of p-CuGaSe2 thin film absorbers, powder of single-phas e CuGaSe2 with defined optical and electrical properties is required as pre cursor material for solar cells. The motivation for this work was that thin films shall be produced by a chemical Vapour transport method using iodine as transport agent. Here we report on an optimised synthesis method of thi s precursor material and discuss the effect of Ag-doping using Ag, AgSe2 an d AgJ as dopants. Crystalline material was characterised by intensity-depen dent photoluminescence (PL), X-ray diffraction (XRD)and time resolved micro wave conductivity (TRMC). PL-measurements at T = 10 K of undoped CuGaSe2 sh ow a dominating emission at E = 1.67 eV which is attributed to a free-to-bo und transition where the acceptor bound state is assigned to copper vacanci es. Ag-doped samples showed a dominating emission at E = 1.61 eV which is a ttributed to a donor acceptor pair-transition with copper vacancies as acce pters and selenium vacancies as donors. XRD-measurements showed good single -phase quality of CuGaSe2. TRMC-measurements reveal an increase of the hole mobility of Ag-doped material compared to undoped CuGaSe2. (C) 1999 Publis hed by Elsevier Science B.V. All rights reserved. PACS: 82.60.J; 61.72; 78. 55; 71.55.