# 2D Atomic Templating for the Large-Scale Synthesis of Metastable CuInS2 and Its Heterojunctions

## TL;DR

A new method for making high-quality CuInS2 material is developed, enabling better performance in energy technologies.

## Contribution

A novel atomic templating strategy enables large-scale synthesis of phase-pure CuInS2 and its heterojunctions.

## Key findings

- The atomic templating method produces phase-pure wurtzite CuAu-type CuInS2.
- The synthesis mechanism involves strain-mediated cation exchange for precise control.
- The approach enables scalable growth of 2D heterojunctions with improved optoelectronic and thermoelectric performance.

## Abstract

CuInS2 has emerged as a promising material
for sustainable
energy technologies due to its combination of attractive electronic,
economic, and ecological properties. However, current synthesis routes
exhibit limited phase uniformity and degraded optoelectronic performance
due to the complex Cu–In–S phase diagram. In this work,
we report a synthesis strategy that overcomes these limitations and
can produce CuInS2 with a singular crystalline phase. An
atomic templating approach is described that retains the structural
order of a two-dimensional (2D) transition-metal monochalcogenide
host to realize phase-pure wurtzite CuAu-type CuInS2. Structural
and spectroscopic characterization confirms the exclusive formation
of this metastable phase and provides insights into its electronic
properties. The transformation proceeds via a strain-mediated layer-by-layer
cation-exchange mechanism, enabling precise control over its extent
and interfaces. This approach establishes a generalizable route for
synthesizing complex 2D heterostructures, and we demonstrate the direct
growth of ternary 2D heterojunctions at large scale. The potential
of this capability was highlighted through the realization of optoelectronic
and thermoelectric devices with enhanced performance.