University of California

Michael J Ford

Guillermo C Bazan

Rachel A Segalman

Hengbin Wang

Colin Richard Bridges

The present disclosure describes additives that attenuate a specific transport channel in ambipolar semiconductors to achieve unipolar characteristics. Carrier selective traps are included in the ambipolar semiconductors and are chosen on the basis of energetic preferences for holes or electrons and the relative positions of the molecular orbital energies of host polymer and the dopants. In one embodiment, a composition of matter useful as a current transport region in an organic semiconductor device comprises a semiconducting polymer; and means for accepting holes (e.g., a hole trapping compound) injected into the current transport region so as to impede conduction of the holes in the semiconducting polymer. This simple solution-processable method can improve the on and off current ratios (I/I) of OFETs by up to three orders of magnitude. Moreover, the treatment yields tailored blends that can be used to fabricate complementary inverters with excellent gain and low-power characteristics.

Organic semiconductor solution blends for switching ambipolar transport to N-type transport

The present disclosure demonstrates that the introduction of electron deficient fullerene acceptors into thin films comprised of the high-mobility semiconducting polymers suppresses an undesirable 'double-slope' in the current-voltage characteristics, improves operational stability, and changes ambipolar transport to unipolar transport. Examination of a variety of high &#x3bc; polymers shows general applicability. The present disclosure also shows that instability is further reduced by tuning the relative electron affinity of the polymer and fullerene by creating blends containing different fullerene derivatives and semiconductor polymers. One can obtain hole &#x3bc; values up to 5.6 cmVsthat are remarkably stable over multiple bias-sweeping cycles. The results provide a simple, solution-processable route to dictate transport properties and improve semiconductor performance in systems that display similar non-idealities.

Stable organic field-effect transistors by incorporating an electron-accepting molecule

Design of side chains yielding highly amphiphilic conjugated polymers is proven to be an effective and general method to access lyotropic liquid crystalline mesophases, allowing greater control over crystalline morphology and improving transistor performance. The general strategy enables variations in structure and interactions that impact alignment and use of liquid crystalline alignment methods. Specifically, solvent-polymer interactions are harnessed to facilitate the formation of high quality polymer crystals in solution. Crystallinity developed in solution is then transferred to the solid state, and thin films of donor-acceptor copolymers cast from lyotropic solutions exhibit improved crystalline order in both the alkyl and &#x3c0;-stacking directions. Due to this improved crystallinity, transistors with active layers cast from lyotropic solutions exhibit a significant improvement in carrier mobility compared to those cast from isotropic solution. One or more embodiments of the present invention achieve a maximum carrier mobility of 0.61 cmVs.

Formation and structure of lyotropic liquid crystalline mesophases in donor-acceptor semiconducting polymers

Conjugated polymer-based organic field-effect transistors have garnered attention since the solution processability of the semiconductor material raises the possibility of lower device fabrication costs, and considerable progress has been made on achieving high mobility systems. Further improvements in charge carrier mobility while using non-specialized deposition techniques and minimizing the volume of semiconductor used in the fabrication process are important considerations for practical implementation. Here, a method of fabricating devices is disclosed that uses a technique (for example, a scalable blade-coating technique) to cast polymer thin film devices from blend solutions with one component being the polymer semiconductor and the other being a commodity polymer. Even when mixing the semiconducting polymer with 90% polystyrene by weight, an average mobility of 2.7&#xb1;0.4 cmVscan be obtained.

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Santa Barbara, CA, United States of America

Michael J Ford