Encapsulation of crystalline and amorphous Sb2S3 within carbon and boron nitride nanotubes

The recent rediscovery of 1D and quasi-1D (q-1D) van der Waals (vdW) crystals has laid foundation for the realization of emergent electronic, optical, and quantum-confined physical phenomena in both bulk and at the nanoscale. Of these, the highly anisotropic q-1D vdW crystal structure and the visible-light optical/optoelectronic properties of antimony trisulfide (Sb2S3) have led to its widespread consideration as a promising building block for photovoltaic and non-volatile phase change devices. However, while these applications will greatly benefit from well-defined and sub-nanometer-thick q-1D structures, little has been known about feasible synthetic routes that can access single covalent chains of Sb2S3. In this work, we explore how encapsulation in single or multi-walled carbon nanotubes (SWCNTs or MWCNTs) and visible-range transparent boron nitride nanotubes (BNNTs) influences the growth and phase of Sb2S3 nanostructures. We demonstrate that nanotubes with smaller diameters had a more pronounced effect in the crystallographic growth direction and orientation of Sb2S3 nanostructures, promoting the crystallization of the guest structures along the long-axis [010]-direction. As such, we were able to reliably access well-ordered few to single covalent chains of Sb2S3 when synthesized within defect-free SWCNTs with sub-2 nm inner diameters. Intriguingly, we found that the degree of crystalline order of Sb2S3 nanostructures was strongly influenced by the presence of defects and discontinuities along the Sb2S3-nanotube interface. We show that amorphous nanowire domains of Sb2S3 form around defect sites in larger, multi-walled nanotubes that manifest inner wall defects and discontinuities, suggesting a means to manipulate the crystallization dynamics of confined sub-10 nm-thick Sb2S3 nanostructures within nanotubes. Lastly, we show that ultranarrow amorphous Sb2S3 can impart functionality onto isolable BNNTs with photocurrent generation in the pA range which, alongside the dispersibility of the Sb2S3@BNNTs, could be leveraged to easily fabricate photoresistors only a few nm in width. Altogether, our results serve to solidify the understanding of how q-1D vdW pnictogen chalcogenides crystallize within confined synthetic platforms and are a step towards realizing functional materials from ensembles of encapsulated heterostructures.

Precursor Engineering of Solution-Processed Sb2 S3 Solar Cells

Antimony-based chalcogenides have emerged as promising candidates for next-generation thin film photovoltaics. Particularly, binary Sb2 S3 thin films have exhibited great potential for optoelectronic applications, due to the facile and low-cost fabrication, simple composition, decent charge transport and superior stability. However, most of the reported efficient Sb2 S3 solar cells are realized based on chemical bath deposition and hydrothermal methods, which require large amount of solution and are normally very time-consuming. In this work, Ag ions are introduced within the Sb2 S3 sol-gel precursors, and effectively modulated the crystallization and charge transport properties of Sb2 S3 . The crystallinity of the Sb2 S3 crystal grains are enhanced and the charge carrier mobility is increased, which resulted improved charge collection efficiency and reduced charge recombination losses, reflected by the greatly improved fill factor and open-circuit voltage of the Ag incorporated Sb2 S3 solar cells. The champion devices reached a record high power conversion efficiency of 7.73% (with antireflection coating), which is comparable with the best photovoltaic performance of Sb2 S3 solar cells achieved based on chemical bath deposition and hydrothermal techniques, and pave the great avenue for next-generation solution-processed photovoltaics.

Molecular precursor-mediated facile synthesis of photo-responsive stibnite Sb2S3 nanorods and tetrahedrite Cu12Sb4S13 nanocrystals

Stibnite Sb₂S₃ and tetrahedrite Cu₁₂Sb₄S₁₃ nanostructures being economical, environmentally benign and having a high absorption coefficient are highly promising materials for energy conversion applications. However, producing these materials especially tetrahedrite in the phase pure form is a challenging task. In this report we present a structurally characterized single source molecular precursor [Sb(4,6-Me₂pymS)₃] for the facile synthesis of binary Sb₂S₃ as well as ternary Cu₁₂Sb₄S₁₃ in oleylamine (OAm) at a relatively lower temperature. The as-prepared Sb₂S₃ and Cu₁₂Sb₄S₁₃ nanostructures were thoroughly checked for their phase purity, elemental composition and morphology by powder X-ray diffraction (pXRD), electron dispersive spectroscopy (EDS) and electron microscopy techniques. pXRD and EDS studies confirm the formation of phase pure, crystalline orthorhombic Sb₂S₃ and cubic Cu₁₂Sb₄S₁₃. The SEM, TEM and HRTEM images depict the formation of well-defined nanorods and nearly spherical nanocrystals for Sb₂S₃ and Cu₁₂Sb₄S₁₃, respectively. The Sb₂S₃ nanorods and Cu₁₂Sb₄S₁₃ nanocrystals exhibit an optical bandgap of ∼1.88 and 2.07 eV, respectively, which are slightly blue-shifted relative to their bulk bandgap, indicating the quantum confinement effect. Finally, efficient photoresponsivity and good photo-stability were achieved in the as-prepared Sb₂S₃ and Cu₁₂Sb₄S₁₃ nanostructure-based prototype photo-electrochemical cell, which make them promising candidates for alternative low-cost photon absorber materials.

Dopant-free hole-transporting materials for stable Sb2(S,Se)3 solar cells

Herein, we demonstrate that a thiophene-modified quinoxaline core small molecule can be applied in Sb₂(S,Se)₃ solar cells. We reveal that the interaction between thiophene and Sb₂(S,Se)₃ through the Sb-S bond essentially improves the interfacial hole-extraction ability. This study provides a cost-effective dopant-free hole-transporting material for inorganic thin film solar cell applications with excellent stability.

Optimization of the Sb2S3 Shell Thickness in ZnO Nanowire-Based Extremely Thin Absorber Solar Cells

Extremely thin absorber (ETA) solar cells made of ZnO/TiO2/Sb2S3 core-shell nanowire heterostructures, using P3HT as the hole-transporting material (HTM), are of high interest to surpass solar cell efficiencies of their planar counterpart at lower material cost. However, no dimensional optimization has been addressed in detail, as it raises material and technological critical issues. In this study, the thickness of the Sb2S3 shell grown by chemical spray pyrolysis is tuned from a couple of nanometers to several tens of nanometers, while switching from a partially to a fully crystallized shell. The Sb2S3 shell is highly pure, and the unwanted Sb2O3 phase was not formed. The low end of the thickness is limited by challenges in the crystallization of the Sb2S3 shell, as it is amorphous at nanoscale dimensions, resulting in the low optical absorption of visible photons. In contrast, the high end of the thickness is limited by the increased density of defects in the bulk of the Sb2S3 shell, degrading charge carrier dynamics, and by the incomplete immersion of the P3HT in the structure, resulting in the poor hole collection. The best ETA solar cell with a short-circuit current density of 12.1 mA/cm2, an open-circuit voltage of 502 mV, and a photovoltaic conversion efficiency of 2.83% is obtained for an intermediate thickness of the Sb2S3 shell. These findings highlight that the incorporation of both the absorber shell and HTM in the core-shell heterostructures relies on the spacing between individual nanowires. They further elaborate the intricate nature of the dimensional optimization of an ETA cell, as it requires a fine-balanced holistic approach to correlate all the dimensions of all the components in the heterostructures.

Phase transition mechanism and bandgap engineering of Sb2S3 at gigapascal pressures

Earth-abundant antimony trisulfide (Sb₂S₃), or simply antimonite, is a promising material for capturing natural energies like solar power and heat flux. The layered structure, held up by weak van-der Waals forces, induces anisotropic behaviors in carrier transportation and thermal expansion. Here, we used stress as mechanical stimuli to destabilize the layered structure and observed the structural phase transition to a three-dimensional (3D) structure. We combined in situ x-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible spectroscopy, and first-principles calculations to study the evolution of structure and bandgap width up to 20.1 GPa. The optical band gap energy of Sb₂S₃ followed a two-step hierarchical sequence at approximately 4 and 11 GPa. We also revealed that the first step of change is mainly caused by the redistribution of band states near the conduction band maximum. The second transition is controlled by an isostructural phase transition, with collapsed layers and the formation of a higher coordinated bulky structure. The band gap reduced from 1.73 eV at ambient to 0.68 eV at 15 GPa, making it a promising thermoelectric material under high pressure.

Combination of full-coverage Sb2S3 thin films and spiro-OMeTAD:P3HT hybrid hole transporting materials for efficient solar cells

The Sb₂S₃ solar cell with a full-coverage Sb₂S₃ thin film and high-hole-mobility spiro-OMeTAD:P3HT hybrid hole transporting material achieved a PCE of 5.65%.

Thermoelectric Properties of Sb-S System Compounds from DFT Calculations

By combining density functional theory, quantum theory of atoms in molecules and transport properties calculations, we evaluated the thermoelectric properties of Sb-S system compounds and shed light on their relationships with electronic structures. The results show that, for Sb2S3, the large density of states (DOS) variation induces a large Seebeck coefficient. Taking into account the long-range weak bonds distribution, Sb2S3 should exhibit low lattice thermal conductivity. Therefore, Sb2S3 is promising for thermoelectric applications. The insertion of Be atoms into the Sb2S3 interstitial sites demonstrates the electrical properties and Seebeck coefficient anisotropy and sheds light on the understanding of the role of quasi-one-dimensional structure in the electron transport. The large interstitial sites existing in SbS2 are at the origin of phonons anharmonicity which counteracts the thermal transport. The introduction of Zn and Ga atoms into these interstitial sites could result in an enhancement of all the thermoelectric properties.