Increasing global demand for energy, along with dwindling fossil fuel resources and a better understanding of the hidden costs associated with these energy sources, have spurred substantial political, academic, and industrial interest in alternative energy resources. Photovoltaics based on organic semiconductors have emerged as promising low-cost alternatives for electricity generation that relies on sunlight. In this tutorial review we discuss the relevance of these organic photovoltaics beginning with some of the economic drivers for these technologies. We then examine the basic properties of these devices, including operation and materials requirements, in addition to presenting the development of the field from a historical perspective. Potential future directions are also briefly discussed. This tutorial review is intended to be an essential overview of the progress of the field, in addition to aiding in the discussion of the future of OPV technologies.
This
study explores the role of very small changes in poly(3-hexylthiophene-2,5-diyl)
(P3HT) regioregularity on the physical and electronic properties of
P3HT nanowires. Due to a high level of synthetic control, we are able
to isolate the effects of regioregularity from those of polymer molecular
weight and dispersity for the first time. A series of P3HTs with regioregularities
from 96 to 99%, similar molecular weights, and low dispersities are
synthesized. The charge transport properties of these polymers, along
with a Soxhlet extracted 93% regioregular P3HT purchased from Rieke
metals, are investigated in both thin film and nanowire transistors.
The resulting structural characteristics are examined by atomic force
microscopy and X-ray diffraction, and the optical characteristics
are explored by UV–vis absorption. It is found that increasing
the P3HT regioregularity results in improved charge transport characteristics,
with an increase in mobility by a factor of 4 for the regioregularities
examined. The increased mobility is shown to reflect increasing structural
coherence lengths in the (010) direction, as well as improved J-aggregate
characteristics due to greater planarity and reduced numbers of defect
sites along the polymer nanowires. Overall, this study serves to emphasize
the importance of determining and reporting even small changes in
polymer regioregularity.
Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm. Electrochemical oxidative doping of these films was used to manipulate their near surface composition and effective work function. Doped states of the P3MT film are maintained even after the sample is removed from solution and potential control confirming the robustness of the films. Such materials with controllable thicknesses and electronic properties have the potential to be useful as interlayer materials for organic electronic applications.
This review provides a general overview on the recent advances for organic-based thermoelectrics with an emphasis on the most thoroughly investigated material classes and the approaches employed to control their thermoelectric transport properties.
In this work, we study the electronic and atomic structural modifications occurring in TiO 2 anatase nanoparticles as anode materials in Naion batteries upon sodiation and desodiation. The structural investigation is performed over both long-and short-range order by combining a comprehensive extended X-ray absorption fine structure (EXAFS) characterization with X-ray diffraction (XRD). The evolution of the electronic structure upon cycling is qualitatively investigated by X-ray absorption near-edge structure (XANES) analysis. The goal of this work is to correlate the outstanding electrochemical performance of carbon-coated TiO 2 anatase nanoparticles in sodium batteries with the electronic and structural modifications induced during the sodiation and desodiation processes upon cycling. This work also demonstrates for the first time a coherent explanation of the structural changes observed, where an electrochemically induced short-range ordering is revealed upon cycling.
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