# Rb4CuSb2Cl11 and Rb2In0.91(0.2)Sb0.09Cl5·H2O: Wide Band Gap 0D Metal Halide Semiconductors

## TL;DR

Researchers discovered new lead-free inorganic halide semiconductors with unique structures and optical properties suitable for optoelectronic applications.

## Contribution

The discovery of a new zero-dimensional lead-free halide structure and a related compound with vacancy-ordered perovskite structure and yellow emission.

## Key findings

- Rb4CuSb2Cl11 has an indirect band gap of 2.89 eV and high electrical resistivity.
- Rb2In0.91(0.2)Sb0.09Cl5·H2O exhibits broad-band yellow emission with a photoluminescence quantum yield of 18.2%.
- The compounds expand the chemical phase space for functional quaternary metal halides.

## Abstract

Herein, we report the discovery, structural and photophysical
characterization
of a new zero-dimensional (0D) lead-free all-inorganic halide, Rb4CuSb2Cl11, which adopts a new structure
type. Single-crystal X-ray diffraction (SCXRD) shows that the structure
consists of isolated, distorted seesaw [SbCl4]− and trigonal planar [CuCl3]2– units,
separated by Rb+ cations that provide charge balance. Optoelectronic
measurements and density functional theory (DFT) calculations indicate
an indirect band gap of 2.89 eV, making it a candidate for wide-bandgap
optoelectronic applications. Electrical resistivity was measured at
1.29 × 1010 Ω·cm, and the trap-state density
(n
trap) was found to be 7.44 × 1010 cm–3. Attempts to synthesize substitution
analogs of Rb4CuSb2Cl11 led to the
synthesis of Rb2In0.91(0.2)Sb0.09Cl5·H2O, which was erroneously reported
as Rb2SbCl5O in a previous study. Rb2In0.91(0.2)Sb0.09Cl5·H2O adopts a vacancy-ordered perovskite structure and exhibits
broad-band yellow emission under UV excitation. The measured photoluminescence
quantum yield (PLQY) for Rb2In0.91(0.2)Sb0.09Cl5·H2O is 18.2%. These findings
add to the growing class of quaternary metal halides with multiple
cation and anion compositions, expanding the chemical phase space
for the discovery of new materials with functional properties.