  Hybrid organic-inorganic perovskites have been established as good candidate
materials for emerging photovoltaics, with device efficiencies of over 22 %
being reported. There are currently only two organic cations, methylammonium
and formamidinium, which produce 3D perovskites with band gaps suitable for
photovoltaic devices. Numerous computational studies have identified
azetidinium as a potential third cation for synthesizing organic-inorganic
perovskites, but to date no experimental reports of azetidinium containing
perovskites have been published. Here we prepare azetidinium lead iodide for
the first time and show that it is a stable, bright orange material that can be
successfully used as the absorber layer in solar cells. We also show that it is
possible to make mixed cation devices by adding the azetidinium cation to
methylammonium lead iodide. Mixed azetidinium-methylammonium cells show
improved performance and reduced hysteresis compared to methylammonium lead
iodide cells.
