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Graham K.R.,University of Florida | Stalder R.,University of Florida | Wieruszewski P.M.,University of Florida | Patel D.G.,University of Florida | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2013

Tailor-made additives, which are molecules that share the same molecular structure as a parent molecule with only slight structural variations, have previously been demonstrated as a useful means to control crystallization dynamics in solution. For example, tailor-made additives can be added to solutions of a crystallizing parent molecule to alter the crystal growth rate, size, and shape. We apply this strategy as a means to predictably control morphology in molecular bulk-heterojunction (BHJ) photovoltaic cells. Through the use of an asymmetric oligomer substituted with a bulky triisobutylsilyl end group, the morphology of BHJ blends can be controlled resulting in a near doubling (from 1.3 to 2.2%) in power conversion efficiency. The use of tailor-made additives provides promising opportunities for controlling crystallization dynamics, and thereby film morphologies, for many organic electronic devices such as photovoltaics and field-effect transistors. © 2012 American Chemical Society. Source


Li Z.,University of Queensland | Du A.J.,Center for Computational Molecular Science | Sun Q.,Center for Computational Molecular Science | Aljada M.,Center for Organic Photonics and Electronics | And 8 more authors.
Chemical Communications | Year: 2011

Co 2+-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires. © 2011 The Royal Society of Chemistry. Source


Chen S.,University of Florida | Tsang S.-W.,University of Florida | Small C.E.,University of Florida | Reynolds J.R.,Center for Organic Photonics and Electronics | So F.,University of Florida
IEEE Photonics Journal | Year: 2012

Inverted bulk heterojunction polymer solar cells have become the preferred device architecture for roll-to-roll (R2R) processing, which allows large area devices to be fabricated on flexible substrates. Significant improvements in inverted solar cell performance have been made with novel photovoltaic polymers, along with optimized blend morphology and improved carrier extraction materials. For the first time, inverted polymer solar cells display their potential for low-cost R2R processing with power conversion efficiencies exceeding 8%. © 2012 IEEE. Source


Li Z.,University of Queensland | Du A.J.,Center for Computational Molecular Science | Sun Q.,Center for Computational Molecular Science | Aljada M.,Center for Organic Photonics and Electronics | Lu G.Q.,University of Queensland
Nanoscale | Year: 2012

Field-effect transistors (FETs) fabricated from undoped and Co 2+-doped CdSe colloidal nanowires show typical n-channel transistor behaviour with gate effect. Exposed to microscope light, a 10 times current enhancement is observed in the doped nanowire-based devices due to the significant modification of the electronic structure of CdSe nanowires induced by Co 2+-doping, which is revealed by theoretical calculations from spin-polarized plane-wave density functional theory. © 2012 The Royal Society of Chemistry. Source


Stalder R.,George and Josephine Butler Polymer Research Laboratory | Xie D.,George and Josephine Butler Polymer Research Laboratory | Zhou R.,University of Florida | Xue J.,University of Florida | And 3 more authors.
Chemistry of Materials | Year: 2012

Three linear asymmetrically functionalized conjugated molecules composed of five or six aromatic rings were synthesized, bearing a terminal phosphonic acid group, with the objective of enabling their grafting onto inorganic CdSe nanocrystals. These chromophores - oligo(phenylene ethynylenes), oligothiophenes, or donor-acceptor-donor oligothiophenes with a benzothiadiazole acceptor - were designed with decreasing HOMO-LUMO energy gaps such that increasing amounts of light could be absorbed toward the longer wavelengths up to 600 nm. Electrochemical measurements show that the energy offsets between the HOMO and LUMO energies of the organic molecules and the energy bands of the CdSe nanocrystals are well-suited for charge transfer between the organic and inorganic components. The characteristics of each component's excited state are studied by fluorescence spectroscopy and the interaction between the conjugated molecules and the CdSe nanocrystals in dilute solutions is monitored by photoluminescence quenching. In the latter experiments, where ester and acid derivatives are compared, the pronounced difference in luminescence quenching supports the ability of the phosphonic acid groups to strongly anchor onto the surface of the nanocrystals. Moreover, these results suggest that charge transfer likely occurs between the organic and the inorganic compounds, and appropriate ratios for the corresponding organic/inorganic hybrids preparation are identified. The preparation by direct ligand exchange and the photophysical properties of the hybrids are described, and spectroscopic analysis estimates that the nanocrystals are covered, on average, with 100-200 electroactive organic molecules. The incident photon-to-electron conversion efficiency reflects the solution absorption of the hybrids because it shows the response from both organic and inorganic components. © 2012 American Chemical Society. Source

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