Solution‐phase synthesis and deposition of earth‐abundant metal chalcogenide semiconductors

The solution phase deposition of inorganic semiconductors is crucial for the commercial‐scale fabrication of thin‐film based devices such as photovoltaics, thermoelectrics, and field effect transistors. The need for a truly dissolved inorganic semiconductor is highlighted by inexpensive high throughput processes such as spray coating and roll‐to‐roll printing that allow for large area and flexible substrate deposition, which are especially desirable for photovoltaic device commercialization. We have addressed the challenge of creating inks of several inorganic semiconductors via two low temperature techniques: 1) the dissolution and deposition of bulk tin sulfide (SnS) thin films using a hydrazine‐free solvent mixture and 2) the solution‐phase synthesis of tungsten selenide (WSe₂), tin selenide (SnSe), and nickel sulfide (NiS) nanoparticles. The indirect band gaps of SnS, WSe₂, and SnSe (1.1 eV, 1.2 eV, and 0.9 eV, respectively) make them attractive for light harvesting applications. In addition, SnS has been reported as a highly efficient photoelectrode material for water splitting, while WSe₂ has been incorporated into highly efficient photoelectrochemical devices (PCE = 17%). The methods we have developed allow for the facile solution‐phase deposition of films by spin‐coating for SnS and SnSe or by evaporation for WSe₂ and NiS. The materials are shown to be phase pure via powder XRD, SEM-EDS, diffuse reflectance UV-vis-NIR, Raman, and high resolution TEM; while the organic content in the films is shown to be greatly reduced using FT-IR. The SnS and SnSe thin film electrodes exhibit a p-type electrochemical photoresponse, and the films made with WSe₂ nanosheets show a high conductivity of up to 92 S cm⁻¹ after annealing.