Core Levels, Band Alignments, and Valence-Band States in CuSbS2 for Solar Cell Applications

Influence of Sulfurization Time on Sb2S3 Synthesis Using a New Graphite Box Design

In recent years, antimony sulfide (Sb2S3) has been investigated as a photovoltaic absorber material due to its suitable absorber coefficient, direct band gap, extinction coefficient, earth-abundant, and environmentally friendly constituents. Therefore, this work proposes Sb2S3 film preparation by an effective two-step process using a new graphite box design and sulfur distribution, which has a high repeatability level and can be scalable. First, an Sb thin film was deposited using the RF-Sputtering technique, and after that, the samples were annealed with elemental sulfur into a graphite box, varying the sulfurization time from 20 to 50 min. The structural, optical, morphological, and chemical characteristics of the resulting thin films were analyzed. Results reveal the method's effectivity and the best properties were obtained for the sample sulfurized during 40 min. This Sb2S3 thin film presents an orthorhombic crystalline structure, elongated grains, a band gap of 1.69 eV, a crystallite size of 15.25 Å, and a nearly stoichiometric composition. In addition, the formation of a p-n junction was achieved by depositing silver back contact on the Glass/FTO/CdS/Sb2S3 structure. Therefore, the graphite box design has been demonstrated to be functional to obtain Sb2S3 by a two-step process.

Chemical and electronic structure of the heavily intermixed (Cd,Zn)S:Ga/CuSbS2 interface

The interface formation and chemical and electronic structure of the (Cd,Zn)S:Ga/CuSbS2 thin-film solar cell heterojunction was studied using hard X-ray photoelectron spectroscopy (HAXPES) of the bare absorber and a buffer/absorber...

Microwave-Assisted Synthesis of Nitrogen and Sulphur Doped Graphene Decorated with Antimony Oxide: An Effective Catalyst for Oxygen Reduction Reaction

In this study, we report on the facile synthesis of a novel electrocatalysts for the oxygen reduction reaction (ORR), based on reduced graphene oxide (RGO), functionalized with metallic and non-metallic elements. In particular, thanks to a fast one-pot microwave-assisted procedure, we induced, in the RGO graphene lattice, a combined doping with nitrogen and sulphur, and the simultaneous decoration with antimony oxide nanocrystals. The multi-doped-decorated material shows enhanced catalytic performance towards ORR, with respect to common nitrogen- or sulphur-doped carbon-based materials. The presence of co-doping is confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy analysis. The detailed electrochemical characterization shows the simultaneous effects of dopant atoms on the catalytic behavior. In particular, the importance of nitrogen and sulphur atoms in driving the oxygen absorption, together with the role of antimony in enhancing the electrochemical performance toward the ORR, are discussed.

Emerging Chalcogenide Thin Films for Solar Energy Harvesting Devices

Chalcogenide semiconductors offer excellent optoelectronic properties for their use in solar cells, exemplified by the commercialization of Cu(In,Ga)Se₂- and CdTe-based photovoltaic technologies. Recently, several other chalcogenides have emerged as promising photoabsorbers for energy harvesting through the conversion of solar energy to electricity and fuels. The goal of this review is to summarize the development of emerging binary (Sb₂X₃, GeX, SnX), ternary (Cu₂SnX₃, Cu₂GeX₃, CuSbX₂, AgBiX₂), and quaternary (Cu₂ZnSnX₄, Ag₂ZnSnX₄, Cu₂CdSnX₄, Cu₂ZnGeX₄, Cu₂BaSnX₄) chalcogenides (X denotes S/Se), focusing especially on the comparative analysis of their optoelectronic performance metrics, electronic band structure, and point defect characteristics. The performance limiting factors of these photoabsorbers are discussed, together with suggestions for further improvement. Several relatively unexplored classes of chalcogenide compounds (such as chalcogenide perovskites, bichalcogenides, etc.) are highlighted, based on promising early reports on their optoelectronic properties. Finally, pathways for practical applications of emerging chalcogenides in solar energy harvesting are discussed against the backdrop of a market dominated by Si-based solar cells.

Enhanced thermoelectric performance in polymorphic heavily Co-doped Cu2SnS3 through carrier compensation by Sb substitution

Heavily acceptor-doped Cu₂SnS₃ (CTS) shows promisingly large power factor (PF) due to its rather high electrical conductivity (σ) which causes a modest ZT with a high electronic thermal conductivity (κ_e ). In the present work, a strategy of carrier compensation through Sb-doping at the Sn site in Cu₂Sn_0.8Co_0.2S₃ was investigated, aiming at tailoring electrical and phonon transport properties simultaneously. Rietveld analysis suggested a complex polymorphic microstructure in which the cation-(semi)ordered tetragonal phase becomes dominant over the coherently bonded cation-disordered cubic phase, as is preliminarily revealed using TEM observation, upon Sb-doping and Sb would substitute Sn preferentially in the tetragonal structure. With increasing content of Sb, the σ was lowered and the Seebeck coefficient (S) was enhanced effectively, which gave rise to high PFs maintained at ~10.4 μWcm^-1K^-2 at 773 K together with an optimal reduction in κ_e by 60-70% in the whole temperature range. The lattice thermal conductivity was effectively suppressed from 1.75 Wm^-1K^-1 to ~1.2 Wm^-1K^-1 at 323 K while maintained very low at 0.3-0.4 Wm^-1K^-1 at 773 K. As a result, a peak ZT of ~0.88 at 773 K has been achieved for Cu₂Sn_0.74Sb_0.06Co_0.2S₃, which stands among the tops so far of the CTS-based diamond-like ternary sulfides. These findings demonstrate that polymorphic microstructures with cation-disordered interfaces as an approach to achieve effective phonon-blocking and low lattice thermal conductivity, of which further crystal chemistry, microstructural and electrical tailoring are possible by appropriate doping.

Recent Advancements and Future Prospects in Ultrathin 2D Semiconductor-Based Photocatalysts for Water Splitting

Ultrathin two-dimensional (2D) semiconductor-mediated photocatalysts have shown their compelling potential and have arguably received tremendous attention in photocatalysis because of their superior thickness-dependent physical, chemical, mechanical and optical properties. Although numerous comprehensions about 2D semiconductor photocatalysts have been amassed up to now, low cost efficiency, degradation, kinetics of charge transfer along with recycling are still the big challenges to realize a wide application of 2D semiconductor-based photocatalysis. At present, most photocatalysts still need rare or expensive noble metals to improve the photocatalytic activity, which inhibits their commercial-scale application extremely. Thus, developing less costly, earth-abundant semiconductor-based photocatalysts with efficient conversion of sunlight energy remains the primary challenge. In this review, it begins with a brief description of the general mechanism of overall photocatalytic water splitting. Then a concise overview of different types of 2D semiconductor-mediated photocatalysts is given to figure out the advantages and disadvantages for mentioned semiconductor-based photocatalysis, including the structural property and stability, synthesize method, electrochemical property and optical properties for H2/O2 production half reaction along with overall water splitting. Finally, we conclude this review with a perspective, marked on some remaining challenges and new directions of 2D semiconductor-mediated photocatalysts.

Synthesis of CuSbS2 Nanoplates and CuSbS2-Cu3SbS4 Nanocomposite: Effect of Sulfur Source on Different Phase Formation

Layered CuSbS₂ and related ternary metal chalcogenides have attracted huge research interest due to their potential applications in sustainable energy storage, photovoltaics, and related area. Here, we report facile synthesis of CuSbS₂ nanoplates and CuSbS₂-Cu₃SbS₄ nanocomposite using hot injection method with varying sulfur precursors. Elemental sulfur (S₈) as sulfur precursor results in nanoplates of pure CuSbS₂, while thioacetamide (TA) as sulfur source gives nanocomposite with Cu₃SbS₄ nanoparticle decorated on the surface of CuSbS₂ nanoplates. The ease of reduction of TA as compared to sulfur at high temperature, in the presence of oleylamine, promotes the oxidation of antimony from (III) to (V) state and the formation of Cu₃SbS₄ phase containing Sb(V). Raman scattering study confirms the presence of Cu₃SbS₄ phase in CuSbS₂-Cu₃SbS₄ nanocomposite. X-ray photoemission spectroscopy study on CuSbS₂ nanoplates and CuSbS₂-Cu₃SbS₄ nanocomposite confirms the desired valence state of the constituent elements. Electrochemical properties measurement shows better specific capacitance for CuSbS₂-Cu₃SbS₄ nanocomposite (151 F/g) as compared to CuSbS₂ nanoplates along with long-term cyclic stability with 68.2% capacitance retention.

Band Alignments, Band Gap, Core Levels, and Valence Band States in Cu3BiS3 for Photovoltaics

The earth-abundant semiconductor Cu₃BiS₃ (CBS) exhibits promising photovoltaic properties and is often considered analogous to the solar absorbers copper indium gallium diselenide (CIGS) and copper zinc tin sulfide (CZTS) despite few device reports. The extent to which this is justifiable is explored via a thorough X-ray photoemission spectroscopy (XPS) analysis: spanning core levels, ionization potential, work function, surface contamination, cleaning, band alignment, and valence-band density of states. The XPS analysis overcomes and addresses the shortcomings of prior XPS studies of this material. Temperature-dependent absorption spectra determine a 1.2 eV direct band gap at room temperature; the widely reported 1.4-1.5 eV band gap is attributed to weak transitions from the low density of states of the topmost valence band previously being undetected. Density functional theory HSE06 + SOC calculations determine the band structure, optical transitions, and well-fitted absorption and Raman spectra. Valence band XPS spectra and model calculations find the CBS bonding to be superficially similar to CIGS and CZTS, but the Bi³⁺ cations (and formally occupied Bi 6s orbital) have fundamental impacts: giving a low ionization potential (4.98 eV), suggesting that the CdS window layer favored for CIGS and CZTS gives detrimental band alignment and should be rejected in favor of a better aligned material in order for CBS devices to progress.

Copper antimony sulfide thin films for visible to near infrared photodetector applications

Ternary chalcostibite copper antimony sulfide (CuSbS₂) is an emerging semiconductor material having applications in photovoltaics, energy storage and optoelectronics due to its high absorption coefficient, suitable bandgap, and it consists of non-toxic and earth abundant elements. CuSbS₂ thin films are prepared by combining chemical bath deposition (antimony sulfide (Sb₂S₃)) and thermal evaporation (copper (Cu)) followed by a heat treatment and their application as visible to near infrared photodetectors is reported. Crystalline structure, elemental composition, chemical state, morphology and optoelectronic properties of the films were characterized by various techniques. The effect of three different Cu thicknesses (CAS 20, CAS 30 and CAS 40 nm) on the photodetection properties are evaluated under illumination using light emitting diodes (LEDs) and a laser. The photodetectors fabricated are successfully tested under different wavelengths, power densities and applied voltage and their photoresponse cyclic stability for each wavelength of illumination was recorded. From the sensitivity calculations, the sample with 20 nm Cu thickness (CAS 20) showed higher detection sensitivity for visible to near infrared wavelengths. Better responsivity results were obtained for CAS 40 because of its improved crystallinity and phase purity. Photodetector properties such as sensitivity and responsivity are evaluated for all the samples. These results are beneficial for cost effective and environment friendly photodetectors and optoelectronic devices based on CuSbS₂ thin films.

Copper antimony sulfide (CuSbS₂) thin films for visible to near infrared photodetection