. Those estimated charge carrier diffusion
lengths were based on the planar structures without employing a
mesoporous TiO2 layer. The longer electron diffusion length up to
1.5 mm was evaluated for the CH3NH3PbI3 perovskite solar cell with
the 650 nm-thick mesoporous TiO2 layer [38], which indicates that
the submicrometer TiO2 layer hardly limits the photocurrent in
perovskite solar cells.