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Chalcogen-based materials like Cu2ZnSnS4 (CZTS) have attracted extensive attention for applications such as photovoltaics and water splitting. However, an inability to monitor the sulfur partial pressure (PS2) during the non-equilibrium annealing process at high temperatures complicates the synthesis of CZTS with controlled optoelectronic properties. Here we demonstrate that PS2 can be monitored by investigating the Sn-S phase transformation. We showed that PS2 drops considerably over the annealing time, causing gradual alterations in CZTS: (i) a change in defect type and (ii) evolution of ZnS and SnxSy phases. With additional ordering treatment, we observed that the low room-temperature photoluminescence energy usually seen in CZTS can result from insufficient PS2 during annealing. It is proven that remarkable Voc beyond 700 mV for solar cells with nonoptimal CdS buffer can be repeatedly achieved when CZTS is prepared under a sufficiently high PS2. An ordering treatment before CdS deposition can further improve Voc to 783 mV. [ABSTRACT FROM AUTHOR]

Tin monosulfide (SnS) is a promising light-absorbing material with weak environmental constraints for application in thin film solar cells. In this paper, we present low-temperature atomic layer deposition (ALD) of high-purity SnS of both cubic and orthorhombic phases. Using tin(II) 2,4-pentanedionate [Sn(acac)2] and hydrogen sulfide (H2S) as precursors, controlled growth of the two polymorphs is achieved. Quartz crystal microbalance measurements are used to establish saturated conditions and show that the SnS ALD is self-limiting over temperatures from at least 80 to 160 °C. In this temperature window, a stable mass gain of 19 ng cm-2 cycle-1 is observed. The SnS thin film crystal structure and morphology undergo significant changes depending on the conditions. High-resolution transmission electron microscopy and X-ray diffraction demonstrate that fully saturated growth requires a large H2S dose and results in the cubic phase. Smaller H2S doses and higher temperatures favor the orthorhombic phase. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry. The orthorhombic phase displays a wide (0.3-0.4 eV) Urbach tail in the near-infrared region, ascribed to its nanoscale structural disorder and/or to sulfur vacancy-induced gap states. In contrast, the cubic phase is smooth and void-free and shows a well-defined, direct forbidden-type bandgap of 1.64 eV. [ABSTRACT FROM AUTHOR]

Building hierarchical assemblies from multiple chemically disparate components remains a tremendous challenge. In this study, we explored the co-assembly of a series of amphiphilic phosphole lipids and single-walled carbon nanotubes. Our studies suggest that both the "tweezer-like" conformation and the size of the counteranion of phosphole lipids are critical for constructing such co-assemblies in solution. Processing in hydrocarbons in which the solvent molecules interact weakly with the phosphole lipid further stabilizes these co-assemblies and results in hexagonal structures not observed in the neat constituents alone. Partial removal of solvents results in the formation of gels, with which we are able to induce strong preferential alignment via shear; these gels exhibit anisotropic electrical conductivities in the solid state, with an electrical conductivity that is 4 orders of magnitude higher along the shear direction. [ABSTRACT FROM AUTHOR]

The addition of trialkoxylbenzyloxylsubstituents at the axialposition of conformationally nonplanar SubPc promotes its solid-stateself-assembly. Unlike prior SubPc derivatives, photophysical studiessuggest the presence of intermolecular electronic coupling betweenneighboring cores of SubPc derivatives, the strength of which dependson both the electronic nature of the corewhich we tune throughfluorinationand the extent of van der Waals interactions originatingfrom the alkyl side chains on the trialkoxylbenzyloxyl tail. Modulatingthe relative strength of core–core and van der Waals interactionsintroduces morphological richness and provides access to liquid crystallinehexagonal and smectic phases. When core–core interactions arestrong, thin films of SubPc spontaneously adopt a highly crystallinelamellar structure in the solid state. Thin films of trialkoxylbenzyloxyl-substitutedSubPcs thus support efficient energy and charge transfer given theirintermolecular electronic communication and long-range order. [ABSTRACT FROM AUTHOR]