Preparation of CIGS films by post-selenization of precursors Preparation of CIGS films by post-selenization of precursors Zs. Baji 1, Z. Lábadi 1, Gy. Molnár 1 Z. E. Horváth 1, A.L. Tóth 1, K. Vad 2, I. Bársony 1 1 – Research Centre for Natural Sciences (MFA), Konkoly Thege M. út 29-33, H-1121 Budapest, HUNGARY 2.- Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI) H-4001 Debrecen, P.O. Box 51 Corresponding author: Z. Labadi, Tel: , Fax: Acknowledgement: The authors wish to thank the Hungarian National Science Fund OTKA (Grant No. NK 73424) for the support Experimental SEM morphology of the layers Conclusions Abstract The preparation of CIGS layers with post-selenization of precursors has been examined. Metallic precursors were evaporated consecutively and by flash evaporation. Two different selenization methods have been tested: annealing in Se atmosphere and evaporation of Se followed by post annealing. The optimal selenization method and proper order of evaporation has been established. The CIGS layers were deposited on Si and glass substrates both cleaned in cc.HNO3 and high purity water before deposition. Compositon of the precursor was always kept In:Ga:Cu/0,8:0,2:1. Flash evaporation: Cu, In and Ga were evaporated simultaneously from a single source at ~1x10 -6 mbar background pressure. Estimated temperature of the source was between ºC Sequential depositition: Cu was deposited by pulsed DC magnetron sputtering from a metallic Cu target (10 µs cycle with 10% duty factor, 6*10 -3 mbar Ar working pressure at 50 sccm total gas inlet). The target power was 250W and the target voltage was 290V. In was evaporated at °C source temperature at pressure 2*10 -5 mbar, while Ga evaporation took place at °C and 1,7*10 -5 mbar respectively. Four sequences (i.e. Cu-In-Ga, Cu-Ga-In, In-Ga-Cu and Ga-In-Cu) were tested for post selenization. Two different methods were applied for post selenization. - Evaporation of selenium from a W boat onto the top of the layers followed by an annealing - Annealing of the precursors in closed ampoules under Se atmosphere for 15 minutes at 500°C. Flash evaporated and post-selenized layers showed a homogeneous CIGS structure after 10 minutes selenization. The sequentially evaporated layers give the best result with the In+Ga+Cu deposition sequence Precursor layer inhomogeneity (In and Ga droplets and islands) did not negatively affect the resulting CIGS layer. No Ga accumulation was found at the back contact of the layers, the Ga concentration is uniform across the film thickness.  Selenization in Se atmosphere resulted in homogeneous layers, with a cauliflower-like morphology (left picture). Within the layers the pyramid-like crystallites typical of the chalcopyrite phase are also visible (top right of the poster)  Selenization in Se atmosphere results in ful selenization of the precursor  In case of the consecutively evaporated layers where the copper was at the bottom, hexagonal crystallites are visible all over the surface (right). „Cu on top” sequence has to be preferred Typical EDS elemental map of the metallic precursors: islands of Ga and In are present „Cu on top” samples also shows ga droplets – Ga diffuses out durin sputtering Typical cross-sectional SEM micrograph of selenization with Se evaporation: Metallic sublayer is present at the bottom. Precursor depositon orderSelenizationStructure In+Ga+CuSe evaporation and post annealingCuIn 0,7 Ga 0.3 Se 2 and CuInSe 2 phases with metallic In Ga+In+CuSe evaporation and post annealingCuInSe 2 with some CuIn 0,7 Ga 0.3 Se2 and metallic In Cu+In+GaSe evaporation and post annealingCuInSe 2 phase with (213) orientation, small grains, some Cu and In. Cu+Ga+InSe evaporation and post annealingCuInSe 2 with In and Cu In+Ga+CuSe vapour at 500°C for 20 minutes CuIn 0,7 Ga 0.3 Se2 with a little CuInSe 2 phase present. Ga+In+CuSe vapour at 500°C for 20 minutes CuInSe 2 with a little CuIn 0,7 Ga 0.3 Se 2 Cu+In+GaSe vapour at 500°C for 20 minutes CuIn 0,9 Ga 0.1 Se 2 with some hexagonal CuSe. Cu+Ga+InSe vapour at 500°C for 20 minutesCuInSe 2 and CuIn 0,7 Ga 0.3 Se 2 with a little hexagonal CuSe Flash evaporated from one sourceSe vapour at 500°C for 5 minutesCuIn 0,8 Ga 0.2 Se 2 Flash evaporated from one sourceSe vapour at 500°C for 15 minutesCuIn 0,8 Ga 0.2 Se 2 Flash evaporated from one source Se vapour at 500°C for 20 minutesCuIn 0,7 Ga 0.3 Se 2 SNMS depth profiling (Cu, In, Ga, Se) phases found by XRD CuInGaSe2 layer prepared by flash evaporation SNMS depth profile of a flash evaporated sample – no Ga accumulation observable at the back contact XRD spectra of the flash evaporated samples post-selenized at 500°C. Only peaks of chalcopyrite structure are present, no oxides or other selenides are observable XRD characterization