# Room-Temperature Synthesis and Photodetector Performance of All-Inorganic Lead-Free Cs 3 Bi 2 X 9 (X = Cl, Br, I) Perovskite Nanocrystals

## TL;DR

Researchers developed lead-free perovskite nanocrystals using a room-temperature method and tested their performance in photodetectors.

## Contribution

A room-temperature synthesis method for all-inorganic lead-free Cs3Bi2X9 perovskite nanocrystals and their use in high-performance photodetectors.

## Key findings

- Cs3Bi2Cl9 perovskite showed the largest crystallite size and best photodetector performance.
- Photodetectors based on Cs3Bi2Cl9 achieved a detectivity of 29.6 × 10⁸ Jones and fast response times.
- X-ray and Raman analyses confirmed the successful formation of Cs3Bi2X9 perovskite phases.

## Abstract

All-inorganic halide
perovskites have gained significant interest
as environmentally friendly alternatives to Pb-based perovskites for
optoelectronic applications. Here, we report the preparation of Pb-free
inorganic Cs3Bi2
X
9 (X = Br, I, Cl) perovskite using a simple room-temperature
antisolvent recrystallization method on soda-lime glass substrates.
We thoroughly analyzed and compared the structural, optical, and morphological
properties of these films. X-ray diffraction analysis revealed that
the Cs3Bi2Cl9 perovskite has the
largest crystallite size (51 nm) compared to the Cs3Bi2Br9 and Cs3Bi2I9 perovskites. The perovskite films demonstrated enhanced crystallinity
and exhibited hexagonal and orthorhombic phases with distinct space
groups. Raman spectroscopy confirmed the successful formation of the
Cs3Bi2
X
9 phase.
Field emission scanning electron microscopy analysis showed that
Cs3Bi2
X
9 exhibited
irregular morphologies with noticeable voids across all samples. The
surfaces were predominantly covered with uneven, spherical-like granules.
The surface morphology displays dense packing with evident porosity
and particle sizes ranging from submicrons to a few micrometers. The
elemental analysis of the Cs3Bi2
X
9 perovskite revealed the formation of nearly stoichiometric
films. The light absorption edge of Cs3Bi2
X
9 varied from 1.8 to 3.2 eV, depending on the
halide composition. The formation of Cs3Bi2
X
9 perovskites was confirmed using X-ray photoelectron
spectroscopy analysis. Finally, we fabricated photodetectors based
on Cs3Bi2
X
9. Among
these, the Cs3Bi2Cl9 perovskite-based
photodetector exhibited superior performance, with a detectivity of
29.6 × 108 Jones, photoresponsivity of 1.14 mA/W,
a fast rise time of 0.21 s, a decay time of 0.35 ms, and an internal
quantum efficiency of 2.45 × 10–1 %. These
findings demonstrate the potential of Cs3Bi2Cl9 perovskite-based photodetectors as promising candidates
for next-generation, lead-free photodetector devices.