Electrochemical and electronic devices based on low bandgap polymers

Sammanfattning: The research field of the organic electronics includes light emitting diodes (OLEDs), field-effect transistors (OFETs), polymer photovoltaic cells (PVCs), polymer lasers and electrochemical devices. Recently, organic materials are envisaged for spintronics. This dissertation covers a large research scope ranging from electrochemical devices, light emitting diodes, to field-effect transistors, in both processing techniques and device characterizations.Printed all-organic electrochemical diodes and transistors on flexible plastic or paper substrates have been realized by simple and low-cost method of fabricating. Conducting polymer poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), utilized as active component, is deposited by spin-coating or printing techniques. The devices are directly fabricated from design without the need for masks, patterns or dies. The output characteristics of both half-wave and full-wave rectifier circuits from two-terminal diodes show stable performances at frequencies of 5 Hz. Electrochemical transistors based on both three- and four-terminal configurations have good performances with IONlIoFF current ratios of 103 - 104 at operating voltages below 3 V. The new kind of devices reported are robust and could serve as components in microelectronics, and as redox sensors and detectors since the conductivity of conducting polymers depends on the redox states.Both LEDs and FETs are realized from a low bandgap donor-acceptor-donor (D-A-D) polymer. The polymer consists of fluorene units and donor-acceptor-donor (D-A-D) units. The D-A-D segment includes two electron-donating thiophene rings combined with a thiadiazolo-quinoxaline unit, which is electron withdrawing to its nature. The resulting polymer is conjugated and has a band gap of 1.27 eV. The corresponding electro- and photoluminescence spectra both peak at approximately 1 Ilm, which is largest emission wavelength ever reported to date. The resulting FETs exhibit typical p-channel functions, and relatively high field-effect mobility of 0.03 cm2y-1s-1, near zero threshold voltage and a current on/off ratio of 5 x104 in ambient atmosphere. The mobility value is highest in low bandgap D-A-D polymers ever reported so far.