A device fabrication method is reported to efficiently produce CH3NH3PbI3-based planar perovskite solar cells on polymer substrates with the entire process conducted at 150 degrees C or below. The hole blocking layer employed is a solution processed 100 nm thick mesoporous TiO2 layer. A gas-assisted perovskite deposition method is used to produce excellent coverage of the hole blocking layer by a similar to 350 nm thick CH3NH3PbI3 film, resulting in high device performance reproducibility. We show that an average efficiency of 10.6 +/- 1.2%, and a maximum efficiency of 12.3% are obtained for flexible perovskite solar cells, offering great promise for further improvement of this low-temperature, low-cost processing solar technology. (C) 2014 Elsevier B.V. All rights reserved.