Non-injection synthesis of Cu2ZnSnS4 nanocrystals using a binary precursor and ligand approach

We present a non-injection, one-pot synthesis of kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) that allows for multi-gram yields with precise control of the NCs’ metal composition. This is enabled through the selective use of a binary sulfur precursor and ligand reaction mixture, which acts to decouple the nucleation and growth stages. © 2013, The Royal Society of Chemistry

In situ formation of reactive sulfide precursors in the one-pot, multigram synthesis of Cu2ZnSnS4 nanocrystals

Herein we outline a general one-pot method to produce large quantities of compositionally tunable, kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) through the decomposition of in situ generated metal sulfide precursors. This method uses air stable precursors and should be applicable to the synthesis of a range of metal sulfides. We examine the formation of the ligands, precursors, and particles in turn. Direct reaction of CS2 with the aliphatic primary amines and thiols that already constitute the reaction mixture is used to produce ligands in situ. Through the use of 1H and 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, and optical absorption spectroscopy, we elucidate the formation of the resulting oleyldithiocarbamate and dodecyltrithiocarbonate ligands. The decomposition of their corresponding metal complexes at temperatures of ∼100 °C yields nuclei with a size of 1–2 nm, with further growth facilitated by the decomposition of dodecanethiol. In this way the nucleation and growth stages of the reaction are decoupled, allowing for the generation of NCs at high concentrations. Using in situ X-ray diffraction, we monitor the evolution of our reactions, thus enabling a real-time glimpse into the formation of Cu2ZnSnS4 NCs. For completeness, the surface chemistry and the electronic structure of the resulting CZTS NCs are studied. © 2013, American Chemical Society

Examining the role of ultra-thin atomic layer deposited metal oxide barrier layers on CdTe/ITO interface stability during the fabrication of solution processed nanocrystalline solar cells.

Solution processed CdTe layers are a potentially low-cost alternative for use in thin-film solar cells. We have recently reported the use of such nanocrystalline layers within ITO/CdTe/ZnO/Al device architectures. One key concern with this type of device structure is the possibility of atomic scale interdiffusion between the ITO and CdTe layers, which can result in deleterious n-type doping of the CdTe layer. Rutherford Backscattering has been used to study the chemical composition across the ITO/CdTe interface as a function of thermal annealing temperature. Through these measurements we verify that interdiffision is observed across the interface for annealing temperatures above 200 degrees C, and the extent of interdiffusion increases with temperature. Ultra-thin alumina, zirconia and titania layers deposited between the ITO and CdTe layers have been studied for their potential to act as a diffusion barrier. All investigated barriers successfully suppress interdiffusion. The outcomes of these compositional studies are directly compared to solar cells fabricated under analogous processing conditions, demonstrating improved cell performance. © 2014, Elsevier Ltd

Soft-Lithographed Up-Converted Distributed Feedback Visible Lasers Based on CdSe\u2013CdZnS\u2013ZnS Quantum Dots

The development of a solution-deposited up-converted distributed feedback laser prototype is presented. It employs a sol\u2013gel silica/germania soft-lithographed microcavity and CdSe\u2013CdZnS\u2013ZnS quantum dot/sol\u2013gel zirconia composites as optical gain material. Characterization of the linear and nonlinear optical properties of quantum dots establishes their high absorption cross-sections in the one- and two- photon absorption regimes to be 1 7 10 12 14 cm 2 and 5 7 10 4 GM, respectively. In addition, ultrafast transient absorption dynamics measurements of the graded seal quantum dots reveal that the Auger recombination lifetime is 220 ps, a value two times higher than that of the corresponding CdSe core. These factors enable the use of such quantum dots as optically pumped gain media, operating in the one- and two-photon absorption regime. The incorporation of CdSe\u2013CdZnS\u2013ZnS quantum dots within a zirconia host matrix affords a quantum-dot ink that can be directly deposited on our soft-lithographed distributed feedback grating to form an all-solution-processed microcavity laser

Soft X-ray Detectors Based on SnS Nanosheets for the Water Window Region

The structural characteristics of biological specimens, such as wet proteins and fixed living cells, can be conveniently probed in their host aqueous media using soft X-rays in the water window region (200–600 eV). Conventional X-ray detectors in this area exhibit low spatial resolution, have limited sensitivity, and require complex fabrication procedures. Here, many of these limitations are overcome by introducing a direct soft X-ray detector based on ultrathin tin mono-sulfide (SnS) nanosheets. The distinguishing characteristic of SnS is its high photon absorption efficiency in the soft X-ray region. This factor enables the fabricated soft X-ray detectors to exhibit excellent sensitivity values on the order of (Formula presented.) at peak energies of ≈600 eV. The peak signal is found to be sensitive to the number of stacked SnS layers, with thicker SnS nanosheet assemblies yielding a peak response at higher energies and with peak sensitives of over 2.5 (Formula presented.) at 1 V. Detailed current–voltage and temporal characteristics of these detectors are also presented. These results showcase the excellent performance of SnS nanosheet-based soft X-ray detectors compared to existing direct soft X-ray detectors, including that of the emerging organic–inorganic perovskite class of materials

Improved performance and stability in quantum dot solar cells through band alignment engineering

Solution processing is a promising route for the realization of low-cost, large-area, flexible and lightweight photovoltaic devices with short energy payback time and high specific power. However, solar cells based on solution-processed organic, inorganic and hybrid materials reported thus far generally suffer from poor air stability, require an inert-atmosphere processing environment or necessitate high-temperature processing [superscript 1], all of which increase manufacturing complexities and costs. Simultaneously fulfilling the goals of high efficiency, low-temperature fabrication conditions and good atmospheric stability remains a major technical challenge, which may be addressed, as we demonstrate here, with the development of room-temperature solution-processed ​[ZnO over ​PbS] quantum dot solar cells. By engineering the band alignment of the quantum dot layers through the use of different ligand treatments, a certified efficiency of 8.55% has been reached. Furthermore, the performance of unencapsulated devices remains unchanged for over 150 days of storage in air. This material system introduces a new approach towards the goal of high-performance air-stable solar cells compatible with simple solution processes and deposition on flexible substrates.National Science Foundation (U.S.)Hertz FoundationSamsung Advanced Institute of TechnologyNational Institutes of Health (U.S.) (Massachusetts Institute of Technology. Laser Biomedical Research Center. Contract 9-P41-EB015871-26A1)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (MIT Center for Materials Science and Engineering. Award DMR-08-19762