Organic field-effect transistors (OFETs) have the potential to lead to low-cost flexible displays, wearable electronics, and sensors. While recent efforts have focused greatly on improving the maximum charge mobility that can be achieved in such devices, studies about the stability and reliability of such high performance devices are relatively scarce. In this talk, we will discuss the results of recent studies aimed at improving the stability of OFETs under operation and their shelf lifetime. In particular, we will focus on device architectures where the gate dielectric is engineered to act simultaneously as an environmental barrier layer.
In the past, our group had demonstrated solution-processed top-gate OFETs using TIPS-pentacene and PTAA blends as a semiconductor layer with a bilayer gate dielectric layer of CYTOP/Al2O3, where the oxide layer was fabricated by atomic layer deposition, ALD. Such devices displayed high operational stability with little degradation after 20,000 on/off scan cycles or continuous operation (24 h), and high environmental stability when kept in air for more than 2 years, with unchanged carrier mobility. Using this stable device geometry, simple circuits and sensors operating in aqueous conditions were demonstrated. However, the Al2O3 layer was found to degrade due to corrosion under prolonged exposure in aqueous solutions. In this talk, we will report on the use of a nanolaminate (NL) composed of Al2O3 and HfO2 by ALD to replace the Al2O3 single layer in the bilayer gate dielectric use in top-gate OFETs. Such OFETs were found to operate under harsh condition such as immersion in water at 95 °C.
This work was funded by the Department of Energy (DOE) through the Bay Area Photovoltaics Consortium (BAPVC) under Award Number DE-EE0004946.
We discuss a non-vacuum low-cost reverse stamping method for the realization of circuits based on top-gate organic field-effect transistors (OFETs) with a bi-layer gate dielectric. This method allows for patterning of high-k inorganic dielectric films produced by atomic layer deposition and consequently of the bilayer gate dielectric layers used in our top-gate OFETs. We demonstrate the fabrication and operation of logic inverters and ring oscillators following this approach.
A spectrally resolving quantum dot photodetector has been designed and fabricated which is able to discriminate wavelengths in the visible region. The device consists of a monolayer of 5.4 nm diameter CdSe nanoparticles that have been sandwiched between two organic layers of Hexanedithiol, all on a highly doped p-type InP substrate. A thin, semitransparent layer of gold deposited on the top of the device made the second contact. The two layers of Hexanedithiol act as tunnel barriers for electrons inside the nanoparticles. Changing the bias voltage across the device, causes specific energy states inside the quantum dot to align with the conduction band edge of the InP. Any excited carriers in these energy levels will tunnel trough the organic barrier and be collected as photocurrent. The responsivity and noise equivalent power has been measured for two wavelengths.
A spectrally resolving quantum dot photodetector has been designed and fabricated which is able to discriminate wavelengths in the visible region. The device consists of a monolayer of 5.4 nm diameter CdSe nanoparticles that have been sandwiched between two organic layers of Hexanedithiol, all on a highly doped p-type InP substrate. A thin, semitransparent layer of gold deposited on the top of the device made the second contact. The two layers of Hexanedithiol act as tunnel barriers for electrons inside the nanoparticles. Changing the bias voltage across the device, causes specific energy states inside the quantum dot to align with the conduction band edge of the InP. Any excited carriers in these energy levels will tunnel trough the organic barrier and be collected as photocurrent. By changing the wavelength of the incident light, the device shows a wavelength dependent I-V spectrum with jumps in the current at specific voltages. Comparing which peaks in different wavelengths are present, shows that the device has a spectrally dependent response to the incident light.
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