Planar perovskite solar cells with a p-i-n structure use both hole-transport layers and electron-transport layers to promote collection of photogenerated holes and electrons for achieving high performance, wherein a high temperature processed compact and mesoporous titanium dioxide are usually required. We report here efficient perovsldte solar cells grown directly on ultraviolet-ozone treated fluorine-doped tin oxide (FTO) substrates without using any electron-transport layers. The morphology, structure, optical electrical properties of perovsldte films deposited on FTO substrates with and without ultraviolet-ozone treatment and their corresponding devices' performance have been studied and compared. Ultraviolet ozone treatment of FTO substrates improves the smoothness and coverage of CH3NH3PbI3-xClx films, which avoids direct contact between FTO and hole-transport layer. A planar electron-transport layer free device with a power conversion efficiency of over 10% has been achieved, suggesting that the widely adopted electron-transport layer is not a requirement for an efficient device. (C) 2016 Elsevier B.V. All rights reserved.