Water-Stable 1D Hybrid Tin(II) Iodide Emits Broad Light with 36% Photoluminescence Quantum Efficiency

The
optical and light emission properties of tin and lead halide
perovskites are remarkable because of the robust room-temperature
(RT) performance, broad wavelength tunability, high efficiency, and
good quenching resistance to defects. These highly desirable attributes
promise to transform current light-emitting devices, phosphors, and
lasers. One disadvantage in most of these materials is the sensitivity
to moisture. Here, we report a new air-stable one-dimensional (1D)
hybrid lead-free halide material (DAO)­Sn2I6 (DAO,
1,8-octyldiammonium) that is resistant to water for more than 15 h.
The material exhibits a sharp optical absorption edge at 2.70 eV and
a strong broad orange light emission centered at 634 nm, with a full
width at half-maximum (fwhm) of 142 nm (0.44 eV). The emission has
a long photoluminescence (PL) lifetime of 582 ns, while the intensity
is constant over a very broad temperature range (145–415 K)
with a photoluminescence quantum yield (PLQY) of at least 20.3% at
RT. Above 415 K the material undergoes a structural phase transition
from monoclinic (C2/c) to orthorhombic
(Ibam) accompanied by a red shift in the band gap
and a quench in the photoluminescence emission. Density functional
theory calculations support the trend in the optical properties and
the 1D electronic nature of the structure, where the calculated carrier
effective masses along the inorganic chain are significantly lower
than those perpendicular to the chain. Thin films of the compound
readily fabricated from solutions exhibit the same optical properties,
but with improved PLQY of 36%, for a 60 nm thick film, among the highest
reported for lead-free low-dimensional 2D and 1D perovskites and metal
halides.