Hybrid Dion–Jacobson 2D Lead Iodide Perovskites

The
three-dimensional hybrid organic–inorganic perovskites
have shown huge potential for use in solar cells and other optoelectronic
devices. Although these materials are under intense investigation,
derivative materials with lower dimensionality are emerging, offering
higher tunability of physical properties and new capabilities. Here,
we present two new series of hybrid two-dimensional (2D) perovskites
that adopt the Dion–Jacobson (DJ) structure type, which are
the first complete homologous series reported in halide perovskite
chemistry. Lead iodide DJ perovskites adopt a general formula A′An–1PbnI3n+1 (A′ = 3-(aminomethyl)­piperidinium
(3AMP) or 4-(aminomethyl)­piperidinium (4AMP), A = methylammonium (MA)).
These materials have layered structures where the stacking of inorganic
layers is unique as they lay exactly on top of another. With a slightly
different position of the functional group in the templating cation
3AMP and 4AMP, the as-formed DJ perovskites show different optical
properties, with the 3AMP series having smaller band gaps than the
4AMP series. Analysis on the crystal structures and density functional
theory (DFT) calculations suggest that the origin of the systematic
band gap shift is the strong but indirect influence of the organic
cation on the inorganic framework. Fabrication of photovoltaic devices
utilizing these materials as light absorbers reveals that (3AMP)­(MA)3Pb4I13 has the best power conversion
efficiency (PCE) of 7.32%, which is much higher than that of the corresponding
(4AMP)­(MA)3Pb4I13.