24 research outputs found
Formation of unique nanocrystalline Cu-In-Se bulk pn homojunctions for opto-electronic devices
Semiconductor pn junctions, integrated in optoelectronic devices require high quality crystals, made by expensive, technically difficult processes. Bulk heterojunction (BHJ) structures offer practical alternatives to circumvent the cost, flexibility and scale-up challenges of crystalline planar pn junctions. Fabrication methods for the current organic or inorganic BHJ structures invariably create interface mismatch and low doping issues. To overcome such issues, we devised an innovative approach, founded on novel inorganic material system that ensued from single-step electrodeposited copper-indium-selenide compounds. Surface analytical microscopies and spectroscopies reveal unusual phenomena, electro-optical properties and quantum effects. They support the formation of highly-ordered, sharp, abrupt 3-dimensional nanoscale pn BHJs that facilitate efficient charge carrier separation and transport, and essentially perform the same functions as crystalline planar pn junctions. This approach offers a low-cost processing platform to create nanocrystalline films, with the attributes necessary for efficient BHJ operation. It allows roll-to-roll processing of flexible devices in simple thin-film form factor.Partial funding for this work is provided by customers of Xcel Energy through a grant from the Renewable Development Fund. The authors gratefully acknowledge sample preparation, analytical contributions and useful discussions with Sharmila Menezes and Yan Li (InterPhases Solar); Senli Guo (Brucker Nano); Terrence McGuckin (Ephemeron Labs); and Nassim Rahimi (HORIBA Scientific). A. Samantilleke acknowledges Prof. L. M. Peter (Bath University, UK) for introducing EER technique
Nanocarbon-Based photovoltaics
Carbon materials are excellent candidates for photovoltaic solar cells: they
are Earth-abundant, possess high optical absorption, and superior thermal and
photostability. Here we report on solar cells with active layers made solely of
carbon nanomaterials that present the same advantages of conjugated
polymer-based solar cells - namely solution processable, potentially flexible,
and chemically tunable - but with significantly increased photostability and
the possibility to revert photodegradation. The device active layer composition
is optimized using ab-initio density functional theory calculations to predict
type-II band alignment and Schottky barrier formation. The best device
fabricated is composed of PC70BM fullerene, semiconducting single-walled carbon
nanotubes and reduced graphene oxide. It achieves a power conversion efficiency
of 1.3% - a record for solar cells based on carbon as the active material - and
shows significantly improved lifetime than a polymer-based device. We calculate
efficiency limits of up to 13% for the devices fabricated in this work,
comparable to those predicted for polymer solar cells. There is great promise
for improving carbon-based solar cells considering the novelty of this type of
device, the superior photostability, and the availability of a large number of
carbon materials with yet untapped potential for photovoltaics. Our results
indicate a new strategy for efficient carbon-based, solution-processable, thin
film, photostable solar cells
Synthesis and Optoelectronic Properties of Two-Dimensional FeS<sub>2</sub> Nanoplates
There is a growing interest in the earth abundant and
nontoxic
iron disulfide (FeS<sub>2</sub>) photovoltaic materials. Here, we
report the synthesis of FeS<sub>2</sub> nanoplates with different
spectral features which we have associated with thicknesses and crystallization.
The structure and crystalline order of ultrathin FeS<sub>2</sub> nanoplates
have a strong influence on the carrier lifetime, electronic and optical
properties. We demonstrate that two-dimensional FeS<sub>2</sub> nanoplates
show great promise for fabrication of hybrid bulk heterojunction solar
cells. This opens up a host of applications of these materials as
inexpensive solar cells and photocatalysts
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Characterization of Porous Materials by Fluorescence Correlation Spectroscopy Super-resolution Optical Fluctuation Imaging.
Porous materials such as cellular cytosol, hydrogels, and block copolymers have nanoscale features that determine macroscale properties. Characterizing the structure of nanopores is difficult with current techniques due to imaging, sample preparation, and computational challenges. We produce a super-resolution optical image that simultaneously characterizes the nanometer dimensions of and diffusion dynamics within porous structures by correlating stochastic fluctuations from diffusing fluorescent probes in the pores of the sample, dubbed here as "fluorescence correlation spectroscopy super-resolution optical fluctuation imaging" or "fcsSOFI". Simulations demonstrate that structural features and diffusion properties can be accurately obtained at sub-diffraction-limited resolution. We apply our technique to image agarose hydrogels and aqueous lyotropic liquid crystal gels. The heterogeneous pore resolution is improved by up to a factor of 2, and diffusion coefficients are accurately obtained through our method compared to diffraction-limited fluorescence imaging and single-particle tracking. Moreover, fcsSOFI allows for rapid and high-throughput characterization of porous materials. fcsSOFI could be applied to soft porous environments such hydrogels, polymers, and membranes in addition to hard materials such as zeolites and mesoporous silica
Characterization of Porous Materials by Fluorescence Correlation Spectroscopy Super-resolution Optical Fluctuation Imaging
Porous materials such as cellular cytosol, hydrogels, and block copolymers have nanoscale features that determine macroscale properties. Characterizing the structure of nanopores is difficult with current techniques due to imaging, sample preparation, and computational challenges. We produce a super-resolution optical image that simultaneously characterizes the nanometer dimensions of and diffusion dynamics within porous structures by correlating stochastic fluctuations from diffusing fluorescent probes in the pores of the sample, dubbed here as “fluorescence correlation spectroscopy super-resolution optical fluctuation imaging” or “fcsSOFI”. Simulations demonstrate that structural features and diffusion properties can be accurately obtained at sub-diffraction-limited resolution. We apply our technique to image agarose hydrogels and aqueous lyotropic liquid crystal gels. The heterogeneous pore resolution is improved by up to a factor of 2, and diffusion coefficients are accurately obtained through our method compared to diffraction-limited fluorescence imaging and single-particle tracking. Moreover, fcsSOFI allows for rapid and high-throughput characterization of porous materials. fcsSOFI could be applied to soft porous environments such hydrogels, polymers, and membranes in addition to hard materials such as zeolites and mesoporous silica
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Characterization of Porous Materials by Fluorescence Correlation Spectroscopy Super-resolution Optical Fluctuation Imaging
Porous materials such as cellular cytosol, hydrogels, and block copolymers have nanoscale features that determine macroscale properties. Characterizing the structure of nanopores is difficult with current techniques due to imaging, sample preparation, and computational challenges. We produce a super-resolution optical image that simultaneously characterizes the nanometer dimensions of and diffusion dynamics within porous structures by correlating stochastic fluctuations from diffusing fluorescent probes in the pores of the sample, dubbed here as “fluorescence correlation spectroscopy super-resolution optical fluctuation imaging” or “fcsSOFI”. Simulations demonstrate that structural features and diffusion properties can be accurately obtained at sub-diffraction-limited resolution. We apply our technique to image agarose hydrogels and aqueous lyotropic liquid crystal gels. The heterogeneous pore resolution is improved by up to a factor of 2, and diffusion coefficients are accurately obtained through our method compared to diffraction-limited fluorescence imaging and single-particle tracking. Moreover, fcsSOFI allows for rapid and high-throughput characterization of porous materials. fcsSOFI could be applied to soft porous environments such hydrogels, polymers, and membranes in addition to hard materials such as zeolites and mesoporous silica