Halide perovskite solar cells based on nanocolumnar ZnO are considered alternative candidates to the more established TiO2 based devices. Replacing the scaffold oxide layer by ZnO has the benefit of a larger electron mobility and lower processing temperatures, still reaching power conversion efficiencies (PCEs) of over 15%. The perovskite layer stability and improving the PCE are currently two major issues under investigation. Regarding the latter, the presence of an interfacial layer of Al-doped ZnO (AZO) gives an enhanced power output, as it was recently reported. Using density functional theory calculations we discuss the band alignment at the ZnO (AZO) - halide perovskite interface, indicating one possible source for the enhanced PCE. (C) 2015 Elsevier B.V. All rights reserved.