Regis J. Kline

Contact-induced crystallinity for high-performance soluble acene-based transistors and circuits

The use of organic materials presents a tremendous opportunity to significantly impact the functionality and pervasiveness of large-area electronics. Commercialization of this technology requires reduction in manufacturing costs by exploiting inexpensive low-temperature deposition and patterning techniques, which typically lead to lower device performance. We report a low-cost approach to control the microstructure of solution-cast acene-based organic thin films through modification of interfacial chemistry. Chemically and selectively tailoring the source/drain contact interface is a novel route to initiating the crystallization of soluble organic semiconductors, leading to the growth on opposing contacts of crystalline films that extend into the transistor channel. This selective crystallization enables us to fabricate high-performance organic thin-film transistors and circuits, and to deterministically study the influence of the microstructure on the device characteristics. By connecting device fabrication to molecular design, we demonstrate that rapid film processing under ambient room conditions and high performance are not mutually exclusive.

The Influence of Polymer Purification on Photovoltaic Device Performance of a Series of Indacenodithiophene Donor Polymers

A series of low bandgap indacenodithiophene polymers is purified by recycling SEC in order to isolate narrow polydispersity fractions. This additional purification step is found to have a significant beneficial influence on the solar cell performance and the reasons for this performance increase are investigated.

Use of X-Ray Diffraction, Molecular Simulations, and Spectroscopy to Determine the Molecular Packing in a Polymer-Fullerene Bimolecular Crystal

The molecular packing in a polymer: fullerene bimolecular crystal is determined using X-ray diffraction (XRD), molecular mechanics (MM) and molecular dynamics (MD) simulations, 2D solid-state NMR spectroscopy, and IR absorption spectroscopy. The conformation of the electron-donating polymer is significantly disrupted by the incorporation of the electron-accepting fullerene molecules, which introduce twists and bends along the polymer backbone and 1D electron-conducting fullerene channels.

Influence of source-drain electric field on mobility and charge transport in organic field-effect transistors

We report on a strong field-dependent mobility in organic field-effect transistors fabricated by using poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C14) as the active polymer layer. Charge transport and mobilities in devices annealed in the mesophase show a more pronounced dependence on channel length as compared with as-cast devices. Analysis reveals that the contact effects in both sets of devices are negligible from room temperature down to ≈100K. We show that this field dependence is consistent with a Poole-Frenkel model of mobility. Finally, the nonlinear transport data for short channel devices are modeled consistently in the Poole-Frenkel framework over a broad temperature range.

NIST Standard Reference Material 3600: Absolute Intensity Calibration Standard for Small-Angle X-ray Scattering

The certification of a new NIST standard reference material (SRM) for the calibration of small-angle X-ray scattering intensity is described, including the purpose, use and applicability of the SRM together with limitations and uncertainties in the intensity calibration provided.

Traceable GISAXS measurements for pitch determination of a 25 nm self-assembled polymer grating

The feature sizes of only a few nanometres in modern nanotechnology and next-generation microelectronics continually increase the demand for suitable nanometrology tools. Grazing-incidence small-angle X-ray scattering (GISAXS) is a versatile technique to measure lateral and vertical sizes in the nanometre range, but the traceability of the obtained parameters, which is a prerequisite for any metrological measurement, has not been demonstrated so far. In this work, the first traceable GISAXS measurements, demonstrated with a self-assembled block copolymer grating structure with a nominal pitch of 25 nm, are reported. The different uncertainty contributions to the obtained pitch value of 24.83 (9) nm are discussed individually. The main uncertainty contribution results from the sample–detector distance and the pixel size measurement, whereas the intrinsic asymmetry of the scattering features is of minor relevance for the investigated grating structure. The uncertainty analysis provides a basis for the evaluation of the uncertainty of GISAXS data in a more general context, for example in numerical data modeling.

Distinguishing between nonlinear channel transport and contact effects in organic FETs

We investigate charge injection and transport in organic field-effect transistors fabricated by using poly(2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C14) or poly(3-hexylthiophene) (P3HT) as the active polymer layer. We show that in high mobility devices where the channel resistances are low compared to the contact resistances, the device performance can be dominated by the metal/organic semiconductor (OSC) contacts. However, in sets of devices where the channel resistance is dominant over the contacts (usually the lower mobility devices), we see pronounced field dependence in the saturation regime mobilities consistent with a Poole-Frenkel model of charge transport within the channel. The field-dependent mobility in short-channel devices produces nonlinear output current-voltage characteristics which can be modeled consistently in the Poole-Frenkel framework.