chemistry

Organic electrochemical transistor

Organic electrochemical transistor is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Organic electrochemical transistor rather than just read about it. In short: The organic electrochemical transistor (OECT) is an organic electronic device which functions like a transistor. The current flowing through the device is controlled by the exchange of ions between an electrolyte and the OECT channel composed of an organic conductor or semiconductor.

Key takeaways

Organic electrochemical transistor belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Organic electrochemical transistor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Organic electrochemical transistor from memory before moving on to harder problems.

Reference excerpt

The organic electrochemical transistor (OECT) is an organic electronic device which functions like a transistor. The current flowing through the device is controlled by the exchange of ions between an electrolyte and the OECT channel composed of an organic conductor or semiconductor. The exchange of ions is driven by a voltage applied to the gate electrode which is in ionic contact with the channel through the electrolyte. The migration of ions between the channel and the electrolyte is accompanied by electrochemical redox reactions occurring in the channel material. The electrochemical redox of the channel along with ion migration changes the conductivity of the channel in a process called electrochemical doping. OECTs are being explored for applications in biosensors, bioelectronics and large-area, low-cost electronics. OECTs can also be used as multi-bit memory devices that mimic the synaptic functionalities of the brain. For this reason, OECTs can also be investigated as elements in neuromorphic computing applications.

History of OECTs Organic electrochemical transistors emerged in 1984, when White, Kittlesen, and Wrighton at MIT reported the first “molecule-based” transistor using gold electrodes coated with polypyrrole. By immersing the device in an electrolyte and applying a small voltage, they could switch the polymer between insulating and conducting states and amplify small chemical signals. At the time, this molecule-transistor had no practical application, but there was interest in combining microelectronic devices with chemical and biological systems for sensor applications. Later in 1994, the first partially printed OECT functioned as a small electrochemical enzyme transistor, useful for detecting glucose and hydrogen peroxide. The use of PEDOT: PSS as a stable, printable, and highly conductive polymer also emerged during this period. A decade later, researchers investigated the in-situ redox switching of PEDOT's electronic conductivity, and the first demonstrations of PEDOT-based transistors appeared in 2002. Because of their low operating voltage, OECTs are used in many applications, including health monitoring, biomarkers, neuromorphic computing, and even the monitoring and control of plant development.

OECT device construction and operating mechanism OECTs consist of a semiconductor or even conductor thin-film (the channel), usually made of a conjugated polymer, which is in direct contact with an electrolyte. Source and drain electrodes establish electrical contact to the channel, while a gate electrode establishes electrical contact to the electrolyte. The electrolyte can be liquid, gel, or solid. In the most common biasing configuration, the source is grounded and a voltage (drain voltage) is applied to the drain. This causes a current to flow (drain current), due to electronic charge (usually holes) present in the channel. When a voltage is applied to the gate, ions from the electrolyte are injected in the channel and change the electronic charge density, and hence the drain current. When the gate voltage is removed, the injected ions return to the electrolyte and the drain current goes back to its original value. However, some channel materials can hold the migrated ions even after removing the gate voltage enabling their use as memory devices. OECTs commonly use PEDOT:PSS as the channel material, and work in the depletion mode. The organic semiconductor PEDOT is doped p-type by the sulfonate anions of present in PSS and hence PEDOT:PSS exhibits a high electronic conductivity. When no gate voltage is applied, a high drain current flows through the highly conductive channel, and the OECT is said to be in the ON state. When a positive voltage is applied to the gate, cations from the electrolyte are injected into the PEDOT:PSS channel, where they compensate the negative charge on the sulfonate anions. This leads to electrochemical reduction of PEDOT from its oxidised state to its neutral state resulting in de-doping of the OECT channel. The OECT is then said to be in the OFF state. Accumulation mode OECTs, based on intrinsic organic semiconductors (for example p(g2T-TT)), have also been described. OECTs are different from electrolyte-gated field-effect transistors. In the latter type of device, ions do not penetrate into the channel, but rather accumulate near its surface (or near the surface of a dielectric layer, when such a layer is deposited on the channel). This induces accumulation of electronic charge inside the channel, near the surface. In contrast, in OECTs, ions are injected into the channel and change the electronic charge density throughout its entire volume. As a result of this bulk coupling between ionic and electronic charge, OECTs show a very high transconductance along with an outstanding intrinsic gain. The disadvantage of OECTs is that they are slow, as they are limited by the inherently slow migration of ions into and out of the channel. However, micro-fabricated OECTs show response times of the order of hundreds of microseconds. Accurate simulation of OECTs is possible using the drift-diffusion model. OECTs are currently the focus of intense development for applications in bioelectronics, and in large-area, low-cost electronics. Advantages such as straightforward fabrication and miniaturization, compatibility with low-cost printing techniques, compatibility with a wide range of mechanical supports (including fibers, paper, plastic and elastomer), and stability in aqueous environments, led to their use in a variety of applications in biosensors. Moreover, their high transconductance makes OECTs powerful amplifying transducers. OECTs have been used to detect ions, neurotransmitters, metabolites, DNA, pathogenic organisms, as well as to probe cell adhesion, measure the integrity of barrier tissue, detect epileptic activity in rats, and interface with electrically active cells and tissues.

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Worked examples

Example 1 — a first encounter with Organic electrochemical transistor

Start with the simplest possible case. Write down what Organic electrochemical transistor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Organic electrochemical transistor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Organic electrochemical transistor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Organic electrochemical transistor

In research: Organic electrochemical transistor appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Organic electrochemical transistor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Organic electrochemical transistor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organic electronics, Transistor types, so understanding it makes those chapters shorter.
In everyday life: Look for Organic electrochemical transistor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Organic electrochemical transistor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Organic electrochemical transistor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Organic electrochemical transistor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Organic electrochemical transistor in simple terms?

Why does Organic electrochemical transistor matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Organic electrochemical transistor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Organic electrochemical transistor.