Pyrite Nanocrystal Solar Cells: Promising, or Fool's Gold?

Pyrite-phase iron sulfide (FeS2) nanocrystals were synthesized to form solvent-based dispersions, or "solar paint," to fabricate photovoltaic devices (PVs). Nanocrystals were sprayed onto substrates as absorber layers in devices with several different architectures, including Schottky barrier, heterojunction, and organic/inorganic hybrid architectures, to explore their viability as a PV material. None of the devices exhibited PV response. XRD and Raman spectroscopy confirmed the pyrite composition and phase purity of the nanocrystals. The electrical conductivity of the nanocrystal films was about 4 to 5 S/cm, more typical of metal nanocrystal films than semiconductor nanocrystal films, and the lack of PV response appears to derive from the highly conductive surface-related defects in pyrite that have been proposed.

Silicon nanowire fabric as a lithium ion battery electrode material.

A nonwoven fabric with paperlike qualities composed of silicon nanowires is reported. The nanowires, made by the supercritical-fluid-liquid-solid process, are crystalline, range in diameter from 10 to 50 nm with an average length of >100 µm, and are coated with a thin chemisorbed polyphenylsilane shell. About 90% of the nanowire fabric volume is void space. Thermal annealing of the nanowire fabric in a reducing environment converts the polyphenylsilane coating to a carbonaceous layer that significantly increases the electrical conductivity of the material. This makes the nanowire fabric useful as a self-supporting, mechanically flexible, high-energy-storage anode material in a lithium ion battery. Anode capacities of more than 800 mA h g(-1) were achieved without the addition of conductive carbon or binder.

Solution-liquid-solid synthesis of CuInSe2 nanowires and their implementation in photovoltaic devices.

CuInSe2 (CIS) nanowires were synthesized by solution-liquid-solid (SLS) growth in a high boiling solvent using bismuth nanocrystals as seeds. The nanowires tended to be slightly deficient in In and exhibited either cubic or hexagonal crystal structure, depending on the synthesis conditions. The hexagonal structure, which is not observed in bulk crystals, appears to evolve from large concentrations of twin defects. The nanowires could be compressed into a free-standing fabric or paper-like material. Photovoltaic devices (PVs) were fabricated using the nanowires as the light-absorbing layer to test their viability as a solar cell material and were found to exhibit measurable PV response.

Synthesis of Cu(2)ZnSnS(4) nanocrystals for use in low-cost photovoltaics.

Cu(2)ZnSnS(4) (CZTS) is a promising new material for thin-film solar cells. Nanocrystal dispersions, or solar paints, present an opportunity to significantly reduce the production cost of photovoltaic devices. This communication demonstrates the colloidal synthesis of CZTS nanocrystals and their use in fabricating prototype solar cells with a power conversion efficiency of 0.23% under AM 1.5 illumination.