Oxide-induced grain growth in CZTS nanoparticle coatings

Abstract

An innovative and scalable synthesis approach to the formation of CZTS nanoparticles has been developed using aerosol spray pyrolysis. Surface-ligand-free CZTS nanoparticles with controllable size and composition are synthesized by thermally decomposing an aerosolized precursor mixture of copper, zinc, and tin thiocarbamates. After collection, the particles are dispersed in an organic solvent, coated on soda lime glass, mechanically compacted, and annealed in a low-pressure sulfur atmosphere to form CZTS thin films. The resulting thin film is highly porous and composed of small grains. We have found that growing a thin amorphous oxide layer on the surface of ligand-free Cu 2 ZnSnS 4 (CZTS) nanoparticles substantially enhances uniform grain growth during heat treatment in a sulfur atmosphere. This is achieved by adding a simple annealing step in air after nanoparticle production and before coating. This process consistently results in CZTS films with higher tin content after annealing, suggesting that the presence of an oxide layer around the particles improves the retention of volatile tin sulfide phases, which is then beneficial in respect to grain growth kinetics.

Oxide route for production of Cu2ZnSnS4 solar cells by pulsed laser deposition

“…Several studies have reported an enhancement in grain size under oxygen-annealing conditions, e.g. by employing open air oxidation of CZTS nanoparticles [33], by adding a MoO2 layer on the back contact [34], or by adding a Na2MoO4 layer on the back contact [35]. The SnOxSy layer at the CZTS/Mo interface is present in oxide and oxy-sulfide samples.…”

Fabrication of CZTS Solar Cells Using Electrodeposition Techniques

“…There are many methods by which CZTS can be manufactured. [156], screen printing [157], doctor blade coating [158], slot-die coating [159], roller coating [160] (if flexible substrates are used), and, for lab-scale PV devices, spin-coating [161]. The pre-prepared CZTS that is deposited can come in the form of a nanocrystal ink or paste.…”

“…Once cooled, the CZTS nanocrystals are extracted using a centrifuge, and washed and re-suspended in an organic solvent [164]. Alternative methods of manufacturing CZTS inks include using a spray pyrolysis method, where the dissolved metallic compounds are sprayed through a tube furnace [156], a microwave solution heating method [158,165], and the solid state reaction of copper, zinc, tin and sulphur powders in a furnace followed by ball milling and re-suspension in a solvent [166]. CZTS deposited from inks and pastes still requires sulphurisation or selenisation in order to facilitate grain growth, and selenised films have achieved efficiencies of up to 9.0% [167].…”