A Direct Bandgap Copper–Antimony Halide Perovskite

Since the establishment of perovskite
solar cells (PSCs), there
has been an intense search for alternative materials to replace lead
and improve their stability toward moisture and light. As single-metal
perovskite structures have yielded unsatisfactory performances, an
alternative is the use of double perovskites that incorporate a combination
of metals. To this day, only a handful of these compounds have been
synthesized, but most of them have indirect bandgaps and/or do not
have bandgaps energies well-suited for photovoltaic applications.
Here we report the synthesis and characterization of a unique mixed
metal ⟨111⟩-oriented layered perovskite, Cs4CuSb2Cl12 (1), that incorporates
Cu2+ and Sb3+ into layers that are three octahedra
thick (n = 3). In addition to being made of abundant
and nontoxic elements, we show that this material behaves as a semiconductor
with a direct bandgap of 1.0 eV and its conductivity is 1 order of
magnitude greater than that of MAPbI3 (MA = methylammonium).
Furthermore, 1 has high photo- and thermal-stability
and is tolerant to humidity. We conclude that 1 is a
promising material for photovoltaic applications and represents a
new type of layered perovskite structure that incorporates metals
in 2+ and 3+ oxidation states, thus significantly widening the possible
combinations of metals to replace lead in PSCs.