Various metal oxides are probed as extrinsic thin tunnel barriers in Semiconductor Insulator Semiconductor solar cells. Namely Al2O3, ZrO2, Y2O3, and La2O3 thin films are in between n-type ZnO:Al (AZO) and p-type Si substrates by means of Atomic Layer Deposition. Low reverse dark current-density as low as 3 x 10(-7) A/cm(2), a fill factor up to 71.3%, and open-circuit voltage as high as 527 mV are obtained, achieving conversion efficiency of 8% for the rare earth oxide La2O3. ZrO2 and notably Al2O3 show drawbacks in performance suggesting an adverse reactivity with AZO as also indicated by X-ray Photoelectron Spectroscopy. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.