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Golden, CO, United States

The National Renewable Energy Laboratory , located in Golden, Colorado, is the United States' primary laboratory for renewable energy and energy efficiency research and development. The National Renewable Energy Laboratory is a government-owned, contractor-operated facility, and is funded through the U.S. Department of Energy . This arrangement allows a private entity to operate the lab on behalf of the federal government under a prime contract. NREL receives funding from Congress to be applied toward research and development projects. NREL also performs research on photovoltaics under the National Center for Photovoltaics. NREL has a number of PV research capabilities including research and development, testing, and deployment. NREL's campus houses several facilities dedicated to PV research. Wikipedia.


Zhao Y.,Shanghai JiaoTong University | Zhu K.,National Renewable Energy Laboratory
Journal of the American Chemical Society | Year: 2014

Hybrid organometallic halide perovskite CH3NH 3PbI2Br (or MAPbI2Br) nanosheets with a 1.8 eV band gap were prepared via a thermal decomposition process from a precursor containing PbI2, MABr, and MACl. The planar solar cell based on the compact layer of MAPbI2Br nanosheets exhibited 10% efficiency and a single-wavelength conversion efficiency of up to 86%. The crystal phase, optical absorption, film morphology, and thermogravimetric analysis studies indicate that the thermal decomposition process strongly depends on the composition of precursors. We find that MACl functions as a glue or soft template to control the initial formation of a solid solution with the main MAPbI2Br precursor components (i.e., PbI2 and MABr). The subsequent thermal decomposition process controls the morphology/surface coverage of perovskite films on the planar substrate and strongly affects the device characteristics. © 2014 American Chemical Society. Source


King P.W.,National Renewable Energy Laboratory
Biochimica et Biophysica Acta - Bioenergetics | Year: 2013

The direct conversion of sunlight into biofuels is an intriguing alternative to a continued reliance on fossil fuels. Natural photosynthesis has long been investigated both as a potential solution, and as a model for utilizing solar energy to drive a water-to-fuel cycle. The molecules and organizational structure provide a template to inspire the design of efficient molecular systems for photocatalysis. A clear design strategy is the coordination of molecular interactions that match kinetic rates and energetic levels to control the direction and flow of energy from light harvesting to catalysis. Energy transduction and electron-transfer reactions occur through interfaces formed between complexes of donor-acceptor molecules. Although the structures of several of the key biological complexes have been solved, detailed descriptions of many electron-transfer complexes are lacking, which presents a challenge to designing and engineering biomolecular systems for solar conversion. Alternatively, it is possible to couple the catalytic power of biological enzymes to light harvesting by semiconductor nanomaterials. In these molecules, surface chemistry and structure can be designed using ligands. The passivation effect of the ligand can also dramatically affect the photophysical properties of the semiconductor, and energetics of external charge-transfer. The length, degree of bond saturation (aromaticity), and solvent exposed functional groups of ligands can be manipulated to further tune the interface to control molecular assembly, and complex stability in photocatalytic hybrids. The results of this research show how ligand selection is critical to designing molecular interfaces that promote efficient self-assembly, charge-transfer and photocatalysis. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. © 2013 Elsevier B.V. All rights reserved. Source


Dillon A.C.,National Renewable Energy Laboratory
Chemical Reviews | Year: 2010

Carbon multiwall nanotubes (MWNTs) and single-wall nanotubes (SWNTs) may be employed to improve upon photoconversion and electrical energy storage technologies. Carbon nanotubes have also been employed in PV devices to improve both exciton generation as well as transport of photoexcited carriers. Every SWNT can be considered to be a unique molecule, with different physical properties, depending on its indices, where the chiral vector magnitude denotes the nanotube circumference. The chiral angle is measured between the roll-up vector and the zigzag axis. Carbon multiwall nanotubes have electronic properties similar to those of graphite and are thus semimetals. Similar to SWNTs, a continuous low-cost production method producing MWNTs that are easily purified is required for MWNTs to be incorporated in emerging technologies. Other forms of nanographitic carbons may also prove promising in the development of next-generation renewable energy devices. Source


Beard M.C.,National Renewable Energy Laboratory
Journal of Physical Chemistry Letters | Year: 2011

Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by utilizing the excess energy in the absorbed photons. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron-phonon coupling that cools hot excitons in bulk semiconductors. However, variations in the reported enhanced quantum yields (QYs) have led to disagreements over the role that quantum confinement plays. The enhanced yield of excitons per absorbed photon is deduced from a dynamical signature in the transient absorption or transient photoluminescence and is ascribed to the creation of biexcitons. Extraneous effects such as photocharging are partially responsible for the observed variations. When these extraneous effects are reduced, the MEG efficiency, defined in terms of the number of additional electron-hole pairs produced per additional band gap of photon excitation, is about two times better in PbSe QDs than that in bulk PbSe. Thin films of electronically coupled QDs have shown promise in simple photon-to-electron conversion architectures. If the MEG efficiency can be further enhanced and charge separation and transport can be optimized within QD films, then QD solar cells can lead to third-generation solar energy conversion technologies. © 2011 American Chemical Society. Source


Gregg B.A.,National Renewable Energy Laboratory
Journal of Physical Chemistry Letters | Year: 2011

The role of entropy in charge separation processes is discussed with respect to the dimensionality of the organic semiconductor. In 1-D materials, the change in entropy, ΔS, plays no role, but at higher dimensions, it leads to a substantial decrease in the Coulomb barrier for charge separation. The effects of ΔS are highest in equilibrium systems but decrease and become time-dependent in illuminated organic photovoltaic (OPV) cells. Higher-dimensional semiconductors have inherent advantages for charge separation, and this may be one reason that C 60 and its derivatives, the only truly three-dimensional organic semiconductors yet known, play such an important role in OPV cells. © 2011 American Chemical Society. Source

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