Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors

Marilena I Zappia; Gabriele Bianca; Sebastiano Bellani; Nicola Curreli; Zdeněk Sofer; Michele Serri; Leyla Najafi; Marco Piccinni; Reinier Oropesa-Nuñez; Petr Marvan; Vittorio Pellegrini; Ilka Kriegel; Mirko Prato; Anna Cupolillo; Francesco Bonaccorso

doi:10.1021/acs.jpcc.1c03597

Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors

J Phys Chem C Nanomater Interfaces. 2021 Jun 10;125(22):11857-11866. doi: 10.1021/acs.jpcc.1c03597. Epub 2021 May 26.

Authors

Marilena I Zappia^{1

2}, Gabriele Bianca^{3

4}, Sebastiano Bellani^{1

3}, Nicola Curreli⁵, Zdeněk Sofer⁶, Michele Serri³, Leyla Najafi^{1

3}, Marco Piccinni^{3

4}, Reinier Oropesa-Nuñez^{1

7}, Petr Marvan⁶, Vittorio Pellegrini^{1

3}, Ilka Kriegel⁵, Mirko Prato⁸, Anna Cupolillo², Francesco Bonaccorso^{1

3}

Affiliations

¹ BeDimensional Spa., via Lungotorrente Secca 3D, 16163 Genova, Italy.
² Department of Physics, University of Calabria, Via P. Bucci cubo 31/C, 87036 Rende, CS, Italy.
³ Graphene Labs, Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova, Italy.
⁴ Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, via Dodecaneso 31, 16146 Genoa, Italy.
⁵ Functional Nanosystems, Istituto Italiano di Tecnologia (IIT), via Morego 30, 16163 Genova, Italy.
⁶ Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic.
⁷ Department of Material Science and Engineering, Uppsala University, Box 534, 75121 Uppsala, Sweden.
⁸ Materials Characterization Facility, Istituto Italiano di Tecnologia, via Morego 30, Genova 16163, Italy.

Abstract

Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions. Differently from the most established InSe, GaSe, GeSe, and many other monochalcogenides, bulk GaS has a large band gap of ∼2.5 eV, which increases up to more than 3.0 eV with decreasing its thickness due to quantum confinement effects. Therefore, 2D GaS fills the void between 2D small-band-gap semiconductors and insulators, resulting of interest for the realization of van der Waals type-I heterojunctions in photocatalysis, as well as the development of UV light-emitting diodes, quantum wells, and other optoelectronic devices. Based on theoretical calculations of the electronic structure of GaS as a function of layer number reported in the literature, we experimentally demonstrate, for the first time, the PEC properties of liquid-phase exfoliated GaS nanoflakes. Our results indicate that solution-processed 2D GaS-based PEC-type photodetectors outperform the corresponding solid-state photodetectors. In fact, the 2D morphology of the GaS flakes intrinsically minimizes the distance between the photogenerated charges and the surface area at which the redox reactions occur, limiting electron-hole recombination losses. The latter are instead deleterious for standard solid-state configurations. Consequently, PEC-type 2D GaS photodetectors display a relevant UV-selective photoresponse. In particular, they attain responsivities of 1.8 mA W^-1 in 1 M H₂SO₄ [at 0.8 V vs reversible hydrogen electrode (RHE)], 4.6 mA W^-1 in 1 M Na₂SO₄ (at 0.9 V vs RHE), and 6.8 mA W^-1 in 1 M KOH (at 1.1. V vs RHE) under 275 nm illumination wavelength with an intensity of 1.3 mW cm^-2. Beyond the photodetector application, 2D GaS-based PEC-type devices may find application in tandem solar PEC cells in combination with other visible-sensitive low-band-gap materials, including transition-metal monochalcogenides recently established for PEC solar energy conversion applications.