Wide band gap perovskites such as methylammonium lead bromide are interesting materials for photovoltaic applications because of their potentially high open-circuit voltage. However, the fabrication of high-quality planar films has not been investigated in detail for this material. We report a new synthesis approach for the fabrication of bromide-based perovskite planar films based on the control of the deposition environment. We achieve dense layers with large and perfectly oriented crystallites 5-10 μm in size. Our results show that large crystal sizes can be achieved only for smooth indium-doped tin oxide substrates, whereas lateral perovskite crystal growth is limited for the rougher fluorine-doped tin oxide substrates. We additionally correlate photocurrent and perovskite crystal properties in photovoltaic devices and find that this parameter is maximized for ordered systems, with internal quantum efficiencies approaching unity. Hence, our work not only gives a new pathway to tune morphology and crystal orientation but also demonstrates its importance for planar perovskite solar cells.