Bulg. J. Phys. vol.40 no.3 (2013), pp. 237-246

Influence of the Annealing on the Structural, Optical and Electrical Properties of Transparent Conductive ZnO:Al/Ag/ZnO:Al Multilayer Stacks

K. Lovchinov1, M. Petrov1, O. Angelov1, H. Nichev1, D. Karashanova2, D. Dimova-Malinovska1
1Central laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko chaussee Blvd., 1784 Sofia, Bulgaria
2Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl.109, 1113 Sofia, Bulgaria
Abstract. The multi-layer stacks ZnO:Al(20nm)/Ag(x)/ZnO:Al(20nm) are prepared by r.f. magnetron sputtering on glass substrates with two different thicknesses of the middle Ag film, x = 16 and 20 nm. The ZnO:Al layers are deposited in Ar+H2 atmosphere and the Ag layer in pure Ar. The substrates are not heated during the deposition of films. Two different stack structures are annealed in N2+Hsub>2 at 180°C for 50 min: the two-layer ZnO:Al/Ag(x) which is covered by the top ZnO:Al film after annealing and the three-layer ZnO:Al(20nm)/Ag(x)/ZnO:Al(20nm). Structural, optical and electrical properties of the as-deposited and annealed structures are studied. The TEM, SEM and AFM analysis confirm the semi-continuous structure of the middle Ag layer in the as-deposited stacks and formation of Ag grains after annealing. The grains size increases with the thickness of the Ag layer and after annealing. The transmittance and reflectance spectra of the as-deposited and annealed stacks demonstrate bands associated with Ag electrons plasma oscillations and d-shell electron inter-band transitions. The results are analyzed and explained by the changes in the grains size, interaction between them and overlapping between the quadrupolar and dipolar plasmon resonances. The as-deposited stacks ZnO:Al(20nm)/Ag(x)/ZnO:Al(20nm) demonstrate low resistivity — 9.0×10-5 Ohm.cm (x = 16) and 4.0×10-5 Ohm.cm (x = 20 nm). The resistivity increases slightly after annealing. The study demonstrates potential for application of multilayer structures ZnO:Al(20nm)/Ag(x)/ZnO:Al(20nm) for x = 16 nm and 20 nm at back side conductive electrode with plasmonic properties for improvement of the thin film solar cells with increased light harvesting

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