Nanostructured Semiconducting Polymer Films with Enhanced Crystallinity and Reorientation of Crystalline Domains by Electrospray Deposition (original) (raw)
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Solar Energy Materials and Solar Cells, 2007
Storage of an internal field in a polymeric semiconductor device should be of great interest for applications like photovoltaic solar cells to facilitate exciton dissociation and improve charge transport in the structure. Orientation of polar molecules, contained inside a polymer binder, induces a rectifying effect, behaving as a distributed homojunction within a single polymeric film. To investigate this concept, a new poly(p-phenylenevinylene) (PPV) derivative bearing push-pull like molecules was purposefully designed and synthesized. Effect of polar molecules' orientation on carrier injection and transport properties was studied. In the test systems, we demonstrate an increase of the external quantum efficiency upon orientation. r
Thin Solid Films, 2008
We report investigations of a new purposefully designed and synthesized functionalized soluble poly(p-phenylene vinylene) (PPV) derivative bearing polar diode-like molecules (NLO-PPV). The active polar molecule is the 4-(N-butyl-N-2-hydroxyethyl)-1-nitro-benzene group on the copolymer. The grafting of the push-pull molecule with a donor/transmitter/acceptor structure, possessing a large ground state dipole moment, enables the efficient molecular orientation by a DC-electric field. An internal electric field could be stored in such system, facilitating exciton dissociation and improving charge transport in polymer photovoltaic single-layer devices, resulting in increased efficiency. In the test systems an increase of the external quantum efficiency by a factor of about 1.5 to 2 took place upon orientation of the polar molecules. The effect of orientation on the carrier injection and transport properties depending on the chain orientation direction was evidenced.
Poly-3-hexylthiophene (P3HT) thin films were investigated by X-ray diffraction (XRD) and electron spin resonance (ESR) to reveal the film structure and molecular organization. The XRD data showed a diffraction pattern with a plane separation between the planes containing thiophene rings of 16.0 Å. Comparison between the XRD patterns of powder and thin films of P3HT suggests that the main chains are folded on the substrate. Angular variation of the line position (g-value) of ESR spectra revealed that thiophene ring of P3HT orients along the substrate normal axis. The ESR linewidth varied by the angular rotation, indicating the one-dimensional spin-chain interactions in the P3HT thin films with a linear network of spin-chains. An organic thin-film transistor (OTFT) with P3HT film as a channel layer was then demonstrated. The P3HT films showed conducting characteristics with holes as carriers. The OTFTs indicated a field-effect mobility of 4.93 × 10 − 3 cm 2 /Vs and an on/off ratio of 73 in the accumulation mode.
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Nanoimprint lithography is used to directly pattern the conjugated polymer semiconductor poly(3-hexylthiophene) (P3HT). We obtain trenches with aspect ratios up to 2 and feature sizes as small as 50 nm in this polymer. The application to organic solar cells is shown by creating an interpenetrated donor-acceptor interface, based on P3HT and N, N -ditridecyl-3,4,9,10perylenetetracarboxylic diimide (PTCDI-C 13 ), deposited from the vapor phase to reduce shadow effects. A planarizing layer of spin-coated zinc oxide (ZnO) nanoparticles is used to reduce the roughness of the layer stack. The response of the photovoltaic devices follows the increased interface area, up to a 2.5-fold enhancement.
2012
The aim of this thesis was to elaborate and characterize hybrid oriented and nanostructured thin films composed of a semiconducting polymer, regioregular poly(3-hexylthiophene) (P3HT) and semiconducting CdSe nanocrystals (spheres, rods). Two orientation methods were used: directional epitaxial crystallization and mechanical rubbing. Epitaxied and rubbedfilms of pure P3HT show strong differences in terms of nanomorphology, crystalline order and structure. Epitaxied films possess a lamellar morphology, a 3D crystalline order and fiber symmetry where the P3HT backbones (cP3HT) are aligned along the fiber axis. Rubbed films do not show a lamellar morphology and have a 2D crystalline order with crystalline domains preferentially oriented “flat-on” relative to the substrate. These differences are reflected in the optical properties of the films. The orientation degree achieved in rubbed films strongly depends on the molecular weight of the polymer. There is also a strong anisotropy of the...
Reflectance anisotropy spectroscopy of oriented films of semiconducting polymers
The Journal of Chemical Physics, 2000
We present reflectance anisotropy spectroscopy ͑RAS͒ data for aligned films of luminescent conjugated polymers. Ultrathin films ͑5-10 nm͒ spin-cast onto friction-deposited poly-tetrafluoroethylene ͑PTFE͒ show birefringence and dichroism indicating alignment of the polymer chains with the PTFE axis. The observed dichroism agrees very well with recently published polarized ultraviolet absorption spectra. In particular, the spectrum of a derivative of poly ͑para-phenylene͒ shows the onset of a perpendicular-polarized absorption feature at 5 eV, consistent with recent theoretical predictions. Thick films, prepared by gel-processing in polyethylene ͑PE͒, also show characteristic optical anisotropy, and the RAS results are interpreted in terms of the ellipsometric functions, ⌿ and ⌬.
Film forming properties of electrosprayed organic heterojunctions
The European Physical Journal Applied Physics, 2013
We used the electrospray deposition (ESD) method to fabricate organic photovoltaic devices with poly (3-hexyl-thiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blends of different composition ratios and different organic solvent solution, namely chloroform (CLF) and dichlorobenzene (DCB). The morphology and crystallinity of the active layers were investigated by means of atomic force microscopy (AFM), two-dimensional X-ray diffraction (XRD 2 ) and optical absorption, spreading light on the peculiarities of the present growth technique, involving much faster solvent evaporation and film forming processes, and comparatively much more ordered strutures with less need of thermal annealing processes. The power conversion efficiency (PCE) under AM 1.5G solar simulation obtained for devices deposited from DCB as compared to those deposited from CLF, showed significant improvement, in fair agreement with what was found by the overall characterization of the physical properties.