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.

BeDimensional Spa via Lungotorrente Secca 3D 16163 Genova Italy

Department of Inorganic Chemistry University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Czech Republic

Department of Material Science and Engineering Uppsala University Box 534 75121 Uppsala Sweden

Department of Physics University of Calabria Via P Bucci cubo 31 C 87036 Rende CS Italy

Dipartimento di Chimica e Chimica Industriale Università degli Studi di Genova via Dodecaneso 31 16146 Genoa Italy

Functional Nanosystems Istituto Italiano di Tecnologia via Morego 30 16163 Genova Italy

Graphene Labs Istituto Italiano di Tecnologia via Morego 30 16163 Genova Italy

Materials Characterization Facility Istituto Italiano di Tecnologia via Morego 30 Genova 16163 Italy

Zobrazit více v PubMed

Li X.; Tao L.; Chen Z.; Fang H.; Li X.; Wang X.; Xu J.-B.; Zhu H. Graphene and Related Two-Dimensional Materials: Structure-Property Relationships for Electronics and Optoelectronics. Appl. Phys. Rev. 2017, 4, 02130610.1063/1.4983646. DOI

Xu K.; Yin L.; Huang Y.; Shifa T. A.; Chu J.; Wang F.; Cheng R.; Wang Z.; He J. Synthesis, Properties and Applications of 2D Layered M III X VI (M = Ga, In; X = S, Se, Te) Materials. Nanoscale 2016, 8, 16802–16818. 10.1039/C6NR05976G. PubMed DOI

Cai H.; Gu Y.; Lin Y.-C.; Yu Y.; Geohegan D. B.; Xiao K. Synthesis and Emerging Properties of 2D Layered III–VI Metal Chalcogenides. Appl. Phys. Rev. 2019, 6, 04131210.1063/1.5123487. DOI

Terhell J. C. J. M. Polytypism in the III–VI Layer Compounds. Prog. Cryst. Growth Charact. 1983, 7, 55–110. 10.1016/0146-3535(83)90030-8. DOI

Kuhn A.; Chevy A.; Chevalier R. Refinement of the 2 H GaS β-Type. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1976, 32, 983–984. 10.1107/S0567740876004445. DOI

Kuhn A.; Bourdon A.; Rigoult J.; Rimsky A. Charge-Density Analysis of GaS. Phys. Rev. B 1982, 25, 4081–4088. 10.1103/PhysRevB.25.4081. DOI

Kokh K. A.; Andreev Y. M.; Svetlichnyi V. A.; Lanskii G. V.; Kokh A. E. Growth of GaSe and GaS Single Crystals. Cryst. Res. Technol. 2011, 46, 327–330. 10.1002/crat.201100055. DOI

Brudnyi V. N.; Sarkisov S. Y.; Kosobutsky A. V. Electronic Properties of GaSe, InSe, GaS and GaTe Layered Semiconductors: Charge Neutrality Level and Interface Barrier Heights. Semicond. Sci. Technol. 2015, 30, 11501910.1088/0268-1242/30/11/115019. DOI

Zappia M. I.; Bianca G.; Bellani S.; Serri M.; Najafi L.; Oropesa-Nuñez R.; Martín-García B.; Bouša D.; Sedmidubský D.; Pellegrini V.; et al. Solution-Processed GaSe Nanoflake-Based Films for Photoelectrochemical Water Splitting and Photoelectrochemical-Type Photodetectors. Adv. Funct. Mater. 2020, 30, 190957210.1002/adfm.201909572. DOI

Curreli N.; Serri M.; Zappia M. I.; Spirito D.; Bianca G.; Buha J.; Najafi L.; Sofer Z.; Krahne R.; Pellegrini V.; Bonaccorso F.; et al. Liquid-Phase Exfoliated Gallium Selenide for Light-Driven Thin-Film Transistors. Adv. Electron. Mater. 2021, 7, 200108010.1002/aelm.202001080. DOI

Petroni E.; Lago E.; Bellani S.; Boukhvalov D. W.; Politano A.; Gürbulak B.; Duman S.; Prato M.; Gentiluomo S.; Oropesa-Nuñez R.; et al. Liquid-Phase Exfoliated Indium–Selenide Flakes and Their Application in Hydrogen Evolution Reaction. Small 2018, 14, 180074910.1002/smll.201800749. PubMed DOI

Curreli N.; Serri M.; Spirito D.; Lago E.; Petroni E.; Martín-García B.; Politano A.; Gürbulak B.; Duman S.; Krahne R.; et al. Liquid Phase Exfoliated Indium Selenide Based Highly Sensitive Photodetectors. Adv. Funct. Mater. 2020, 30, 190842710.1002/adfm.201908427. DOI

Bianca G.; Zappia M. I.; Bellani S.; Sofer Z.; Serri M.; Najafi L.; Oropesa-Nuñez R.; Martín-García B.; Hartman T.; Leoncino L.; et al. Liquid-Phase Exfoliated GeSe Nanoflakes for Photoelectrochemical-Type Photodetectors and Photoelectrochemical Water Splitting. ACS Appl. Mater. Interfaces 2020, 12, 48598–48613. 10.1021/acsami.0c14201. PubMed DOI PMC

Gonzalez J. M.; Oleynik I. I. Layer-Dependent Properties of SnS2 and SnSe2Two-Dimensional Materials. Phys. Rev. B 2016, 94, 12544310.1103/PhysRevB.94.125443. DOI

Ho C. H.; Lin S. L. Optical Properties of the Interband Transitions of Layered Gallium Sulfide. J. Appl. Phys. 2006, 100, 08350810.1063/1.2358192. DOI

Ho C. H.; Huang K. W. Visible Luminescence and Structural Property of GaSe1–xSx (0≤x≤1) Series Layered Crystals. Solid State Commun. 2005, 136, 591–594. 10.1016/j.ssc.2005.09.029. DOI

Aulich E.; Brebner J. L.; Mooser E. Indirect Energy Gap in GaSe and GaS. Phys. Status Solidi B 1969, 31, 129–131. 10.1002/pssb.19690310115. DOI

Cingolani A.; Minafra A.; Tantalo P.; Paorici C. Edge Emission in GaSe and GaS. Phys. Status Solidi A 1971, 4, K83–K85. 10.1002/pssa.2210040150. DOI

Chen H.; Li Y.; Huang L.; Li J. Intrinsic Defects in Gallium Sulfide Monolayer: A First-Principles Study. RSC Adv. 2015, 5, 50883–50889. 10.1039/C5RA08329J. DOI

Jung C. S.; Shojaei F.; Park K.; Oh J. Y.; Im H. S.; Jang D. M.; Park J.; Kang H. S. Red-to-Ultraviolet Emission Tuning of Two-Dimensional Gallium Sulfide/Selenide. ACS Nano 2015, 9, 9585–9593. 10.1021/acsnano.5b04876. PubMed DOI

Zhuang H. L.; Hennig R. G. Single-Layer Group-III Monochalcogenide Photocatalysts for Water Splitting. Chem. Mater. 2013, 25, 3232–3238. 10.1021/cm401661x. DOI

Lu Y.; Chen J.; Chen T.; Shu Y.; Chang R.; Sheng Y.; Shautsova V.; Mkhize N.; Holdway P.; Bhaskaran H.; et al. Controlling Defects in Continuous 2D GaS Films for High-Performance Wavelength-Tunable UV-Discriminating Photodetectors. Adv. Mater. 2020, 32, 190695810.1002/adma.201906958. PubMed DOI

Hu P.; Wang L.; Yoon M.; Zhang J.; Feng W.; Wang X.; Wen Z.; Idrobo J. C.; Miyamoto Y.; Geohegan D. B.; et al. Highly Responsive Ultrathin GaS Nanosheet Photodetectors on Rigid and Flexible Substrates. Nano Lett. 2013, 13, 1649–1654. 10.1021/nl400107k. PubMed DOI

Ho C.-H.; Hsieh M.-H.; Wu C.-C. Photoconductance and Photoresponse of Layer Compound Photodetectors in the UV-Visible Region. Rev. Sci. Instrum. 2006, 77, 11310210.1063/1.2369638. DOI

Peng Q.; Guo Z.; Sa B.; Zhou J.; Sun Z. New Gallium Chalcogenides/Arsenene van Der Waals Heterostructures Promising for Photocatalytic Water Splitting. Int. J. Hydrogen Energy 2018, 43, 1599510.1016/j.ijhydene.2018.07.008. DOI

Tsoeu S. E.; Opoku F.; Govender P. P. Tuning the Electronic, Optical and Structural Properties of GaS/C2N van Der Waals Heterostructure for Photovoltaic Application: First-Principle Calculations. SN Appl. Sci. 2020, 2, 34110.1007/s42452-020-2091-y. DOI

Cui Y.; Peng L.; Sun L.; Qian Q.; Huang Y. Two-Dimensional Few-Layer Group-III Metal Monochalcogenides as Effective Photocatalysts for Overall Water Splitting in the Visible Range. J. Mater. Chem. A 2018, 6, 22768–22777. 10.1039/C8TA08103D. DOI

Harvey A.; Backes C.; Gholamvand Z.; Hanlon D.; McAteer D.; Nerl H. C.; McGuire E.; Seral-Ascaso A.; Ramasse Q. M.; McEvoy N.; et al. Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application As Hydrogen Evolution Catalysts. Chem. Mater. 2015, 27, 3483–3493. 10.1021/acs.chemmater.5b00910. DOI

Mishra P.; Singh D.; Sonvane Y.; Ahuja R. Enhancement of Hydrogen Storage Capacity on Co-Functionalized GaS Monolayer under External Electric Field. Int. J. Hydrogen Energy 2020, 45, 12384–12393. 10.1016/j.ijhydene.2020.02.186. DOI

Zhang C. J.; Park S.-H.; Ronan O.; Harvey A.; Seral-Ascaso A.; Lin Z.; McEvoy N.; Boland C. S.; Berner N. C.; Duesberg G. S.; et al. Enabling Flexible Heterostructures for Li-Ion Battery Anodes Based on Nanotube and Liquid-Phase Exfoliated 2D Gallium Chalcogenide Nanosheet Colloidal Solutions. Small 2017, 13, 170167710.1002/smll.201701677. PubMed DOI

Meng X.; He K.; Su D.; Zhang X.; Sun C.; Ren Y.; Wang H.-H.; Weng W.; Trahey L.; Canlas C. P.; et al. Gallium Sulfide-Single-Walled Carbon Nanotube Composites: High-Performance Anodes for Lithium-Ion Batteries. Adv. Funct. Mater. 2014, 24, 5435–5442. 10.1002/adfm.201401002. DOI

Yang S.; Li Y.; Wang X.; Huo N.; Xia J.-B.; Li S.-S.; Li J. High Performance Few-Layer GaS Photodetector and Its Unique Photo-Response in Different Gas Environments. Nanoscale 2014, 6, 2582–2587. 10.1039/C3NR05965K. PubMed DOI

Marvan P.; Mazánek V.; Sofer Z. Shear-Force Exfoliation of Indium and Gallium Chalcogenides for Selective Gas Sensing Applications. Nanoscale 2019, 11, 4310–4317. 10.1039/C8NR09294J. PubMed DOI

Singh D.; Panda P. K.; Mishra Y. K.; Ahuja R. Van Der Waals Induced Molecular Recognition of Canonical DNA Nucleobases on a 2D GaS Monolayer. Phys. Chem. Chem. Phys. 2020, 22, 6706–6715. 10.1039/C9CP06418D. PubMed DOI

Kato K.; Umemura N. Sellmeier Equations for GaS and GaSe and Their Applications to the Nonlinear Optics in GaS_xSe_1–x. Opt. Lett. 2011, 36, 74610.1364/OL.36.000746. PubMed DOI

Allakhverdiev K.; Ismailov F.; Kador L.; Braun M. Second-Harmonic Generation in GaS Crystals. Solid State Commun. 1997, 104, 1–3. 10.1016/S0038-1098(97)00269-X. DOI

Balendhran S.; Walia S.; Nili H.; Sriram S.; Bhaskaran M. Elemental Analogues of Graphene: Silicene, Germanene, Stanene, and Phosphorene. Small 2015, 11, 640–652. 10.1002/smll.201402041. PubMed DOI

Molle A.; Grazianetti C.; Chiappe D.; Cinquanta E.; Cianci E.; Tallarida G.; Fanciulli M. Hindering the Oxidation of Silicene with Non-Reactive Encapsulation. Adv. Funct. Mater. 2013, 23, 4340–4344. 10.1002/adfm.201300354. DOI

Ye F.; Lee J.; Hu J.; Mao Z.; Wei J.; Feng P. X. L. Environmental Instability and Degradation of Single- and Few-Layer WTe 2 Nanosheets in Ambient Conditions. Small 2016, 12, 5802–5808. 10.1002/smll.201601207. PubMed DOI

Jaegermann W.; Schmeisser D. Reactivity of Layer Type Transition Metal Chalcogenides towards Oxidation. Surf. Sci. 1986, 165, 143–160. 10.1016/0039-6028(86)90666-7. DOI

Favron A.; Gaufrès E.; Fossard F.; Phaneuf-Laheureux A. L.; Tang N. Y. W.; Lévesque P. L.; Loiseau A.; Leonelli R.; Francoeur S.; Martel R. Photooxidation and Quantum Confinement Effects in Exfoliated Black Phosphorus. Nat. Mater. 2015, 14, 826–832. 10.1038/nmat4299. PubMed DOI

Walia S.; Sabri Y.; Ahmed T.; Field M. R.; Ramanathan R.; Arash A.; Bhargava S. K.; Sriram S.; Bhaskaran M.; Bansal V.; et al. Defining the Role of Humidity in the Ambient Degradation of Few-Layer Black Phosphorus. 2D Mater. 2016, 4, 01502510.1088/2053-1583/4/1/015025. DOI

Zhou Q.; Chen Q.; Tong Y.; Wang J. Light-Induced Ambient Degradation of Few-Layer Black Phosphorus: Mechanism and Protection. Angew. Chem., Int. Ed. 2016, 55, 11437–11441. 10.1002/anie.201605168. PubMed DOI

Beechem T. E.; Kowalski B. M.; Brumbach M. T.; McDonald A. E.; Spataru C. D.; Howell S. W.; Ohta T.; Pask J. A.; Kalugin N. G. Oxidation of Ultrathin GaSe. Appl. Phys. Lett. 2015, 107, 17310310.1063/1.4934592. DOI

Bergeron A.; Ibrahim J.; Leonelli R.; Francoeur S. Oxidation Dynamics of Ultrathin GaSe Probed through Raman Spectroscopy. Appl. Phys. Lett. 2017, 110, 24190110.1063/1.4986189. DOI

Zhao Q.; Frisenda R.; Gant P.; Perez de Lara D.; Munuera C.; Garcia-Hernandez M.; Niu Y.; Wang T.; Jie W.; Castellanos-Gomez A. Toward Air Stability of Thin GaSe Devices: Avoiding Environmental and Laser-Induced Degradation by Encapsulation. Adv. Funct. Mater. 2018, 28, 180530410.1002/adfm.201805304. DOI

Shi L.; Li Q.; Ouyang Y.; Wang J. Effect of Illumination and Se Vacancies on Fast Oxidation of Ultrathin Gallium Selenide. Nanoscale 2018, 10, 12180–12186. 10.1039/C8NR01533C. PubMed DOI

Guo Y.; Zhou S.; Bai Y.; Zhao J. Oxidation Resistance of Monolayer Group-IV Monochalcogenides. ACS Appl. Mater. Interfaces 2017, 9, 12013–12020. 10.1021/acsami.6b16786. PubMed DOI

Yang C.; Lu P.; Huang W.; Chen J. Mechanical Stabilities and Nonlinear Properties of Monolayer Gallium Sulfide under Tension. Superlattices Microstruct. 2015, 80, 80–90. 10.1016/j.spmi.2014.10.019. DOI

Ma Y.; Dai Y.; Guo M.; Yu L.; Huang B. Tunable Electronic and Dielectric Behavior of GaS and GaSe Monolayers. Phys. Chem. Chem. Phys. 2013, 15, 7098.10.1039/c3cp50233c. PubMed DOI

Guo Y.; Zhou S.; Bai Y.; Zhao J. Defects and Oxidation of Group-III Monochalcogenide Monolayers. J. Chem. Phys. 2017, 147, 10470910.1063/1.4993639. PubMed DOI

Yi M.; Shen Z. A Review on Mechanical Exfoliation for the Scalable Production of Graphene. J. Mater. Chem. A 2015, 3, 11700–11715. 10.1039/C5TA00252D. DOI

Backes C.; Abdelkader A. M.; Alonso C.; Andrieux-Ledier A.; Arenal R.; Azpeitia J.; Balakrishnan N.; Banszerus L.; Barjon J.; Bartali R.; et al. Production and Processing of Graphene and Related Materials. 2D Mater. 2020, 7, 2200110.1088/2053-1583/ab1e0a. DOI

Bonaccorso F.; Bartolotta A.; Coleman J. N.; Backes C. 2D-Crystal-Based Functional Inks. Adv. Mater. 2016, 28, 6136–6166. 10.1002/adma.201506410. PubMed DOI

Coleman J. N.; Lotya M.; O’Neill A.; Bergin S. D.; King P. J.; Khan U.; Young K.; Gaucher A.; De S.; Smith R. J.; Shvets I. V.; et al. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, 568–571. 10.1126/science.1194975. PubMed DOI

Bellani S.; Petroni E.; Del Rio Castillo A. E.; Curreli N.; Martín-García B.; Oropesa-Nuñez R.; Prato M.; Bonaccorso F. Scalable Production of Graphene Inks via Wet-Jet Milling Exfoliation for Screen-Printed Micro-Supercapacitors. Adv. Funct. Mater. 2019, 29, 180765910.1002/adfm.201807659. DOI

Tsikritzis D.; Rogdakis K.; Chatzimanolis K.; Petrović M.; Tzoganakis N.; Najafi L.; Martín-García B.; Oropesa-Nuñez R.; Bellani S.; Del Rio Castillo A. E.; et al. A Two-Fold Engineering Approach Based on Bi 2 Te 3 Flakes towards Efficient and Stable Inverted Perovskite Solar Cells. Mater. Adv. 2020, 1, 450–462. 10.1039/D0MA00162G. DOI

Najafi L.; Bellani S.; Oropesa-nuñez R.; Brescia R.; Prato M.; Pasquale L.; Demirci C.; Drago F.; Martín-garcía B.; Luxa J.; et al. Microwave-Induced Structural Engineering and Pt Trapping in 6R-TaS2 for Hydrogen Evolution. Small 2020, 16, 200337210.1002/smll.202003372. PubMed DOI

Torrisi F.; Coleman J. N. Electrifying Inks with 2D Materials. Nat. Nanotechnol. 2014, 9, 738–739. 10.1038/nnano.2014.218. PubMed DOI

Kang J.; Wells S. A.; Sangwan V. K.; Lam D.; Liu X.; Luxa J.; Sofer Z.; Hersam M. C. Solution-Based Processing of Optoelectronically Active Indium Selenide. Adv. Mater. 2018, 30, 180299010.1002/adma.201802990. PubMed DOI

Late D. J.; Liu B.; Luo J.; Yan A.; Matte H. S. S. R.; Grayson M.; Rao C. N. R.; Dravid V. P. GaS and GaSe Ultrathin Layer Transistors. Adv. Mater. 2012, 24, 3549–3554. 10.1002/adma.201201361. PubMed DOI

Feng W.; Zheng W.; Cao W.; Hu P. Back Gated Multilayer InSe Transistors with Enhanced Carrier Mobilities via the Suppression of Carrier Scattering from a Dielectric Interface. Adv. Mater. 2014, 26, 6587–6593. 10.1002/adma.201402427. PubMed DOI

Bandurin D. A.; Tyurnina A. V.; Yu G. L.; Mishchenko A.; Zólyomi V.; Morozov S. V.; Kumar R. K.; Gorbachev R. V.; Kudrynskyi Z. R.; Pezzini S.; et al. High Electron Mobility, Quantum Hall Effect and Anomalous Optical Response in Atomically Thin InSe. Nat. Nanotechnol. 2017, 12, 223–227. 10.1038/nnano.2016.242. PubMed DOI

Chowdhury C.; Karmakar S.; Datta A. Monolayer Group IV-VI Monochalcogenides: Low-Dimensional Materials for Photocatalytic Water Splitting. J. Phys. Chem. C 2017, 121, 7615–7624. 10.1021/acs.jpcc.6b12080. DOI

Lv X.; Wei W.; Sun Q.; Li F.; Huang B.; Dai Y. Two-Dimensional Germanium Monochalcogenides for Photocatalytic Water Splitting with High Carrier Mobility. Appl. Catal., B 2017, 217, 275–284. 10.1016/j.apcatb.2017.05.087. DOI

Ye Y.; Guo Q.; Liu X.; Liu C.; Wang J.; Liu Y.; Qiu J. Two-Dimensional GeSe as an Isostructural and Isoelectronic Analogue of Phosphorene: Sonication-Assisted Synthesis, Chemical Stability, and Optical Properties. Chem. Mater. 2017, 29, 8361–8368. 10.1021/acs.chemmater.7b02784. DOI

Li Z.; Qiao H.; Guo Z.; Ren X.; Huang Z.; Qi X.; Dhanabalan S. C.; Ponraj J. S.; Zhang D.; Li J.; Zhao J.; Zhong J.; Zhang H. High-Performance Photo-Electrochemical Photodetector Based on Liquid-Exfoliated Few-Layered InSe Nanosheets with Enhanced Stability. Adv. Funct. Mater. 2018, 28, 170523710.1002/adfm.201705237. DOI

Wickramaratne D.; Zahid F.; Lake R. K. Electronic and Thermoelectric Properties of van Der Waals Materials with Ring-Shaped Valence Bands. J. Appl. Phys. 2015, 118, 07510110.1063/1.4928559. DOI

Faraji M.; Yousefi M.; Yousefzadeh S.; Zirak M.; Naseri N.; Jeon T. H.; Choi W.; Moshfegh A. Z. Two-Dimensional Materials in Semiconductor Photoelectrocatalytic Systems for Water Splitting. Energy Environ. Sci. 2019, 12, 59–95. 10.1039/C8EE00886H. DOI

Li Y.; Li Y.-L.; Sa B.; Ahuja R. Review of Two-Dimensional Materials for Photocatalytic Water Splitting from a Theoretical Perspective. Catal. Sci. Technol. 2017, 7, 545–559. 10.1039/C6CY02178F. DOI

Su T.; Shao Q.; Qin Z.; Guo Z.; Wu Z. Role of Interfaces in Two-Dimensional Photocatalyst for Water Splitting. ACS Catal. 2018, 8, 2253–2276. 10.1021/acscatal.7b03437. DOI

Gan X.; Lei D.; Wong K. Y. Two-Dimensional Layered Nanomaterials for Visible-Light-Driven Photocatalytic Water Splitting. Mater. Today Energy 2018, 352–367. 10.1016/j.mtener.2018.10.015. DOI

Luo B.; Liu G.; Wang L. Recent Advances in 2D Materials for Photocatalysis. Nanoscale 2016, 8, 6904–6920. 10.1039/C6NR00546B. PubMed DOI

Hu S.; Zhu M. Ultrathin Two-Dimensional Semiconductors for Photocatalysis in Energy and Environment Applications. ChemCatChem 2019, 11, 6147–6165. 10.1002/cctc.201901597. DOI

Haynes W. M.CRC Handbook Chemistry and Physics; CRC Press, 2016.

Najafi L.; Bellani S.; Martín-García B.; Oropesa-Nunez R.; Del Rio Castillo A. E.; Prato M.; Moreels I.; Bonaccorso F. Solution-Processed Hybrid Graphene Flake/2H-MoS2 Quantum Dot Heterostructures for Efficient Electrochemical Hydrogen Evolution. Chem. Mater. 2017, 29, 5782–5786. 10.1021/acs.chemmater.7b01897. DOI

Najafi L.; Bellani S.; Oropesa-Nuñez R.; Ansaldo A.; Prato M.; Del Rio Castillo A. E.; Bonaccorso F. Doped-MoSe2 Nanoflakes/3d Metal Oxide–Hydr(Oxy)Oxides Hybrid Catalysts for PH-Universal Electrochemical Hydrogen Evolution Reaction. Adv. Energy Mater. 2018, 8, 180176410.1002/aenm.201801764. DOI

Najafi L.; Romano V.; Oropesa-Nuñez R.; Prato M.; Lauciello S.; D’Angelo G.; Bellani S.; Bonaccorso F. Hybrid Organic/Inorganic Photocathodes Based on WS2 Flakes as Hole Transporting Layer Material. Small Struct. 2021, 2, 200009810.1002/sstr.202000098. DOI

Bellani S.; Martín-García B.; Oropesa-Nuñez R.; Romano V.; Najafi L.; Demirci C.; Prato M.; Del Rio Castillo A. E.; Marasco L.; Mantero E.; et al. “Ion Sliding” on Graphene: A Novel Concept to Boost Supercapacitor Performance. Nanoscale Horiz. 2019, 4, 1077–1091. 10.1039/C8NH00446C. DOI

Ansaldo A.; Bondavalli P.; Bellani S.; Del Rio Castillo A. E.; Prato M.; Pellegrini V.; Pognon G.; Bonaccorso F. High-Power Graphene–Carbon Nanotube Hybrid Supercapacitors. ChemNanoMat 2017, 3, 436–446. 10.1002/cnma.201700093. DOI

Jawaid A.; Nepal D.; Park K.; Jespersen M.; Qualley A.; Mirau P.; Drummy L. F.; Vaia R. A. Mechanism for Liquid Phase Exfoliation of MoS2. Chem. Mater. 2016, 28, 337–348. 10.1021/acs.chemmater.5b04224. DOI

Shen G.; Chen D.; Chen P.-C.; Zhou C. Vapor–Solid Growth of One-Dimensional Layer-Structured Gallium Sulfide Nanostructures. ACS Nano 2009, 3, 1115–1120. 10.1021/nn900133f. PubMed DOI

Preparation and Crystal Growth of Materials with Layered Structures; Lieth R. M. A., Ed.; Springer: Dordrecht, Netherlands, 1977.

Late D. J.; Liu B.; Matte H. S. S. R.; Rao C. N. R.; Dravid V. P. Rapid Characterization of Ultrathin Layers of Chalcogenides on SiO2/Si Substrates. Adv. Funct. Mater. 2012, 22, 1894–1905. 10.1002/adfm.201102913. DOI

Hernandez Y.; Nicolosi V.; Lotya M.; Blighe F. M.; Sun Z.; De S.; McGovern I. T.; Holland B.; Byrne M.; Gun’Ko Y. K.; et al. High-Yield Production of Graphene by Liquid-Phase Exfoliation of Graphite. Nat. Nanotechnol. 2008, 3, 563–568. 10.1038/nnano.2008.215. PubMed DOI

Yang L.; Miklavcic S. J. Revised Kubelka-Munk Theory III A General Theory of Light Propagation in Scattering and Absorptive Media. J. Opt. Soc. Am. A 2005, 22, 186610.1364/JOSAA.22.001866. PubMed DOI

Vargas W. E.; Niklasson G. A. Applicability Conditions of the Kubelka-Munk Theory. Appl. Opt. 1997, 36, 558010.1364/AO.36.005580. PubMed DOI

Najafi L.; Taheri B.; Martín-García B.; Bellani S.; Di Girolamo D.; Agresti A.; Oropesa-Nuñez R.; Pescetelli S.; Vesce L.; Calabrò E.; et al. MoS2 Quantum Dot/Graphene Hybrids for Advanced Interface Engineering of a CH3NH3PbI3 Perovskite Solar Cell with an Efficiency of over 20%. ACS Nano 2018, 12, 10736–10754. 10.1021/acsnano.8b05514. PubMed DOI

Antunez P. D.; Torelli D. A.; Yang F.; Rabuffetti F. A.; Lewis N. S.; Brutchey R. L. Low Temperature Solution-Phase Deposition of SnS Thin Films. Chem. Mater. 2014, 26, 5444–5446. 10.1021/cm503124u. DOI

Patel M.; Chavda A.; Mukhopadhyay I.; Kim J.; Ray A. Nanostructured SnS with Inherent Anisotropic Optical Properties for High Photoactivity. Nanoscale 2016, 8, 2293–2303. 10.1039/C5NR06731F. PubMed DOI

Materials Data on GaS by Materials Project. https://www.osti.gov/dataexplorer/biblio/dataset/1200464 (accessed June 4, 2021).

Gasanly N. M.; Aydınlı A.; Özkan H.; Kocabaş C. Temperature Dependence of the First-Order Raman Scattering in GaS Layered Crystals. Solid State Commun. 2000, 116, 147–151. 10.1016/S0038-1098(00)00292-1. DOI

Irwin J. C.; Hoff R. M.; Clayman B. P.; Bromley R. A. Long Wavelength Lattice Vibrations in GaS and GaSe. Solid State Commun. 1973, 13, 1531–1536. 10.1016/0038-1098(73)90205-6. DOI

Jastrzebski C.; Olkowska K.; Jastrzebski D. J.; Wierzbicki M.; Gebicki W.; Podsiadlo S. Raman Scattering Studies on Very Thin Layers of Gallium Sulfide (GaS) as a Function of Sample Thickness and Temperature. J. Phys.: Condens. Matter 2019, 31, 07530310.1088/1361-648X/aaf53b. PubMed DOI

Demirci S.; Avazlı N.; Durgun E.; Cahangirov S. Structural and Electronic Properties of Monolayer Group III Monochalcogenides. Phys. Rev. B 2017, 95, 11540910.1103/PhysRevB.95.115409. DOI

Bellani S.; Najafi L.; Capasso A.; Del Rio Castillo A. E.; Antognazza M. R.; Bonaccorso F. Few-Layer MoS 2 Flakes as a Hole-Selective Layer for Solution-Processed Hybrid Organic Hydrogen-Evolving Photocathodes. J. Mater. Chem. A 2017, 5, 4384–4396. 10.1039/C6TA10572F. DOI

Dohy D.; Lucazeau G.; Revcolevschi A. Raman Spectra and Valence Force Field of Single-Crystalline β Ga2O3. J. Solid State Chem. 1982, 45, 180–192. 10.1016/0022-4596(82)90274-2. DOI

Zhou J.; Chen L.; Wang Y.; He Y.; Pan X.; Xie E. An Overview on Emerging Photoelectrochemical Self-Powered Ultraviolet Photodetectors. Nanoscale 2016, 8, 50–73. 10.1039/C5NR06167A. PubMed DOI

Qiao H.; Huang Z.; Ren X.; Liu S.; Zhang Y.; Qi X.; Zhang H. Self-Powered Photodetectors Based on 2D Materials. Adv. Opt. Mater. 2020, 8, 190076510.1002/adom.201900765. DOI

Tian W.; Wang Y.; Chen L.; Li L. Self-Powered Nanoscale Photodetectors. Small 2017, 13, 170184810.1002/smll.201701848. PubMed DOI

Petroni E.; Lago E.; Bellani S.; Boukhvalov D. W.; Politano A.; Gürbulak B.; Duman S.; Prato M.; Gentiluomo S.; Oropesa-Nuñez R.; et al. Liquid-Phase Exfoliated Indium-Selenide Flakes and Their Application in Hydrogen Evolution Reaction. Small 2018, 14, 180074910.1002/smll.201800749. PubMed DOI

Gray J. L.The Physics of the Solar Cell. In Handbook of Photovoltaic Science and Engineering; John Wiley & Sons, Ltd: Chichester, U.K., 2011; pp 82–129.

Zhang Q.; Jie J.; Diao S.; Shao Z.; Zhang Q.; Wang L.; Deng W.; Hu W.; Xia H.; Yuan X.; et al. Solution-Processed Graphene Quantum Dot Deep-UV Photodetectors. ACS Nano 2015, 9, 1561–1570. 10.1021/acsnano.5b00437. PubMed DOI

Chitara B.; Krupanidhi S. B.; Rao C. N. R. Solution Processed Reduced Graphene Oxide Ultraviolet Detector. Appl. Phys. Lett. 2011, 99, 11311410.1063/1.3640222. DOI

Gomathi P. T.; Sahatiya P.; Badhulika S. Large-Area, Flexible Broadband Photodetector Based on ZnS-MoS 2 Hybrid on Paper Substrate. Adv. Funct. Mater. 2017, 27, 170161110.1002/adfm.201701611. DOI

Sahatiya P.; Jones S. S.; Badhulika S. 2D MoS2–Carbon Quantum Dot Hybrid Based Large Area, Flexible UV–Vis–NIR Photodetector on Paper Substrate. Appl. Mater. Today 2018, 10, 106–114. 10.1016/j.apmt.2017.12.013. DOI

Shelke N. T.; Karche B. R. Hydrothermal Synthesis of WS2/RGO Sheet and Their Application in UV Photodetector. J. Alloys Compd. 2015, 653, 298–303. 10.1016/j.jallcom.2015.08.255. DOI

Bellani S.; Ghadirzadeh A.; Meda L.; Savoini A.; Tacca A.; Marra G.; Meira R.; Morgado J.; Di Fonzo F.; Antognazza M. R. Hybrid Organic/Inorganic Nanostructures for Highly Sensitive Photoelectrochemical Detection of Dissolved Oxygen in Aqueous Media. Adv. Funct. Mater. 2015, 25, 4531–4538. 10.1002/adfm.201500701. DOI

María Girón R.; Marco-Martínez J.; Bellani S.; Insuasty A.; Comas Rojas H.; Tullii G.; Antognazza M. R.; Filippone S.; Martín N. Synthesis of Modified Fullerenes for Oxygen Reduction Reactions. J. Mater. Chem. A 2016, 4, 1428410.1039/C6TA06573B. DOI

Aguirre J.; Medrano N.; Calvo B.; Celma S. Lock-in Amplifier for Portable Sensing Systems. Electron. Lett. 2011, 47, 117210.1049/el.2011.2472. DOI

Yue Z.; Lisdat F.; Parak W. J.; Hickey S. G.; Tu L.; Sabir N.; Dorfs D.; Bigall N. C. Quantum-Dot-Based Photoelectrochemical Sensors for Chemical and Biological Detection. ACS Appl. Mater. Interfaces 2013, 2800–2814. 10.1021/am3028662. PubMed DOI

Zen J. M.; Song Y. S.; Chung H. H.; Hsu C. T.; Kumar A. S. Photoelectrochemical Oxygen Sensor Using Copper-Plated Screen-Printed Carbon Electrodes. Anal. Chem. 2002, 74, 6126–6130. 10.1021/ac020058r. PubMed DOI

Mauritz K. A.; Moore R. B. State of Understanding of Nafion. Chem. Rev. 2004, 104, 4535–4585. 10.1021/cr0207123. PubMed DOI

Holdcroft S. Fuel Cell Catalyst Layers: A Polymer Science Perspective. Chem. Mater. 2014, 26, 381–393. 10.1021/cm401445h. DOI

Zhang C. J.; Liang M.; Park S.-H.; Lin Z.; Seral-Ascaso A.; Wang L.; Pakdel A.; Coileáin C. Ó.; Boland J.; Ronan O.; et al. Extra Lithium-Ion Storage Capacity Enabled by Liquid-Phase Exfoliated Indium Selenide Nanosheets Conductive Network. Energy Environ. Sci. 2020, 13, 2124–2133. 10.1039/D0EE01052A. DOI

Najafi L.; Bellani S.; Castelli A.; Arciniegas M. P.; Brescia R.; Oropesa-Nuñez R.; Martín-García B.; Serri M.; Drago F.; Manna L.; et al. Octapod-Shaped CdSe Nanocrystals Hosting Pt with High Mass Activity for the Hydrogen Evolution Reaction. Chem. Mater. 2020, 32, 2420–2429. 10.1021/acs.chemmater.9b04883. DOI

Rojas H. C.; Bellani S.; Fumagalli F.; Tullii G.; Leonardi S.; Mayer M. T.; Schreier M.; Grätzel M.; Lanzani G.; Di Fonzo F.; et al. Polymer-Based Photocathodes with a Solution-Processable Cuprous Iodide Anode Layer and a Polyethyleneimine Protective Coating. Energy Environ. Sci. 2016, 9, 3710–3723. 10.1039/C6EE01655C. DOI

Bellani S.; Antognazza M. R.; Bonaccorso F. Carbon-Based Photocathode Materials for Solar Hydrogen Production. Adv. Mater. 2019, 31, 180144610.1002/adma.201801446. PubMed DOI

Steier L.; Bellani S.; Rojas H. C.; Pan L.; Laitinen M.; Sajavaara T.; Di Fonzo F.; Grätzel M.; Antognazza M. R.; Mayer M. T. Stabilizing Organic Photocathodes by Low-Temperature Atomic Layer Deposition of TiO 2. Sustainable Energy Fuels 2017, 1, 1915–1920. 10.1039/C7SE00421D. DOI

Fumagalli F.; Bellani S.; Schreier M.; Leonardi S.; Rojas H. C.; Ghadirzadeh A.; Tullii G.; Savoini A.; Marra G.; Meda L.; et al. Hybrid Organic–Inorganic H 2 -Evolving Photocathodes: Understanding the Route towards High Performance Organic Photoelectrochemical Water Splitting. J. Mater. Chem. A 2016, 4, 2178–2187. 10.1039/C5TA09330A. DOI

Peng L.; Hu L.; Fang X. Low-Dimensional Nanostructure Ultraviolet Photodetectors. Adv. Mater. 2013, 25, 5321–5328. 10.1002/adma.201301802. PubMed DOI

Ni P.-N.; Shan C.-X.; Wang S.-P.; Li B.-H.; Zhang Z.-Z.; Zhao D.-X.; Liu L.; Shen D.-Z. Enhanced Responsivity of Highly Spectrum-Selective Ultraviolet Photodetectors. J. Phys. Chem. C 2012, 116, 1350–1353. 10.1021/jp210994t. DOI

Ates E. S.; Kucukyildiz S.; Unalan H. E. Zinc Oxide Nanowire Photodetectors with Single-Walled Carbon Nanotube Thin-Film Electrodes. ACS Appl. Mater. Interfaces 2012, 4, 5142–5146. 10.1021/am301402y. PubMed DOI

Inamdar S. I.; Rajpure K. Y. High-Performance Metal–Semiconductor–Metal UV Photodetector Based on Spray Deposited ZnO Thin Films. J. Alloys Compd. 2014, 595, 55–59. 10.1016/j.jallcom.2014.01.147. DOI

Chen H.; Liu K.; Hu L.; Al-Ghamdi A. A.; Fang X. New Concept Ultraviolet Photodetectors. Mater. Today 2015, 18, 493–502. 10.1016/j.mattod.2015.06.001. DOI

Peng Q.; Xiong R.; Sa B.; Zhou J.; Wen C.; Wu B.; Anpo M.; Sun Z. Computational Mining of Photocatalysts for Water Splitting Hydrogen Production: Two-Dimensional InSe-Family Monolayers. Catal. Sci. Technol. 2017, 7, 2744–2752. 10.1039/C7CY00090A. DOI

Sun L.; Cui Y.; Peng L.; Du J.; Wang S.; Huang Y. Two-Dimensional Blue-Phosphorene-Phase Germanium Monochalcogenide Photocatalysts for Water Splitting: From Ultraviolet to Visible Absorption. J. Catal. 2019, 373, 67–74. 10.1016/j.jcat.2019.03.031. DOI

Ji Y.; Yang M.; Dong H.; Hou T.; Wang L.; Li Y. Two-Dimensional Germanium Monochalcogenide Photocatalyst for Water Splitting under Ultraviolet, Visible to near-Infrared Light. Nanoscale 2017, 9, 8608–8615. 10.1039/C7NR00688H. PubMed DOI

Two-dimensional BiTeI as a novel perovskite additive for printable perovskite solar cells

Liquid-Phase Exfoliation of Bismuth Telluride Iodide (BiTeI): Structural and Optical Properties of Single-/Few-Layer Flakes