10.1021/jz501237m.s001 Fabian C. Hanusch Fabian C. Hanusch Erwin Wiesenmayer Erwin Wiesenmayer Eric Mankel Eric Mankel Andreas Binek Andreas Binek Philipp Angloher Philipp Angloher Christina Fraunhofer Christina Fraunhofer Nadja Giesbrecht Nadja Giesbrecht Johann M. Feckl Johann M. Feckl Wolfram Jaegermann Wolfram Jaegermann Dirk Johrendt Dirk Johrendt Thomas Bein Thomas Bein Pablo Docampo Pablo Docampo Efficient Planar Heterojunction Perovskite Solar Cells Based on Formamidinium Lead Bromide American Chemical Society 2015 cell absorber materials Efficient Planar Heterojunction Perovskite Solar Cells photoexcited species methylammonium counterpart material exhibits BromideThe development bromide perovskite absorbers sintered mesoporous TiO 2 photoanode diffusion lengths bandgap absorber bandgap alkylammonium power conversion efficiencies 2015-12-17 03:56:35 Journal contribution https://acs.figshare.com/articles/journal_contribution/Efficient_Planar_Heterojunction_Perovskite_Solar_Cells_Based_on_Formamidinium_Lead_Bromide/2038383 The development of medium-bandgap solar cell absorber materials is of interest for the design of devices such as tandem solar cells and building-integrated photovoltaics. The recently developed perovskite solar cells can be suitable candidates for these applications. At present, wide bandgap alkylammonium lead bromide perovskite absorbers require a high-temperature sintered mesoporous TiO<sub>2</sub> photoanode in order to function efficiently, which makes them unsuitable for some of the above applications. Here, we present for the first time highly efficient wide bandgap planar heterojunction solar cells based on the structurally related formamidinium lead bromide. We show that this material exhibits much longer diffusion lengths of the photoexcited species than its methylammonium counterpart. This results in planar heterojunction solar cells exhibiting power conversion efficiencies approaching 7%. Hence, formamidinium lead bromide is a strong candidate as a wide bandgap absorber in perovskite solar cells.