Multifunctional Chiral 2D Lead Halide Perovskites with Circularly Polarized Photoluminescence and Piezoelectric Energy Harvesting Properties

Introducing
the chiral spacers to two-dimensional (2D) lead halide
perovskites (LHPs) enables them to exhibit circularly polarized photoluminescence
(CPPL), which could have applications in chiral-optics and spintronics.
Despite that a great deal of effort has been made in this field, the
reported polarization degree of CPPL at ambient conditions is still
very limited, and the integration of multiple functionalities also
remains to be explored. Here we report the structures, CPPL, and piezoelectric
energy harvesting properties of chiral 2D LHPs, [R-1-(4-bromophenyl)­ethylaminium]2PbI4 (R-[BPEA]2PbI4) and [S-1-(4-bromophenyl)­ethylaminium]2PbI4 (S-[BPEA]2PbI4). Our results show that
these chiral perovskites are direct bandgap semiconductors and exhibit
CPPL centered at ∼513 nm with a maximum degree of polarization
of up to 11.0% at room temperature. In addition, the unique configurational
arrangement of the chiral spacers is found to be able to reduce the
interlayer π–π interactions and consequently result
in strong electron–phonon coupling. Furthermore, the intrinsic
chirality of both R-[BPEA]2PbI4 and S-[BPEA]2PbI4 enables
them to be piezoelectric active, and their composite films can be
applied to generate voltages and currents up to ∼0.6 V and
∼1.5 μA under periodic impacting with a strength of 2
N, respectively. This work not only reports a high degree of CPPL
but also demonstrates piezoelectric energy harvesting behavior for
realizing multifunctionalities in chiral 2D LHPs.