Pyrosol-deposited Ga-doped ZnO (GZO) transparent electrodes in GZO/(p+nn+)c-Si solar cells

Abstract

Transparent and conductive Ga-doped ZnO (GZO) thin films were deposited by ultrasonic spray pyrolysis of film-forming solutions (FFS) on silicon and glass. The effect of Ga concentration in the FFS in the range Ga/Zn = 0–15 at% was systematically investigated to obtain GZO films suitable for application in c-Si solar cells. Films of ∼400 nm in thickness deposited under optimized conditions (Ga/Zn = 5–6 at%) exhibited resistivity ρ of 2.0–2.5 mΩ cm (annealed), 3.0–3.7 mΩ cm (aged), an effective absorption Aeff of 4.3–5.6% in the wavelength range 300–1100 nm, increased passivation quality and a pronounced photovoltaic barrier (relative to n-Si) with implied open-circuit voltage of ∼300 mV for heterojunction GZO/n-Si. Obtained ρ values were a record low for 400-nm-thick GZO films produced by spray pyrolysis. Finally, GZO films with a thickness of 250 nm and 400 nm and Ga/Zn ratios of 3 at% and 6 at%, respectively were applied as a front contact in GZO/(p+nn+)c-Si solar cells. Maximal efficiency of 15.7% was achieved by means of a 400-nm-thick film at Ga/Zn = 6 at% with the best combination of passivation and photovoltaic barrier properties and reasonably low ρ and Aeff.