Nanoporous polymer aerogel channels boost soft transistor performance while remaining stretchable and recyclable, offering a single materials platform for high gain biosensors, neuromorphic elements and pressure sensitive electronic skin.
(Nanowerk Spotlight) Stretchable electronics force together requirements that rarely coexist in a single material. A channel that moves electronic charge quickly tends to favor ordered, tightly packed structures. A channel that can sustain large strain must tolerate deformation, swelling, and defects. If that same channel also has to exchange ions with a surrounding electrolyte, it must expose sufficient internal surface area without losing mechanical integrity. Each improvement in one direction pressure tests the others.
Organic electrochemical transistors sit at the center of this problem. They rely on ions penetrating a polymer channel and modulating its conductivity. High transconductance demands that ions access a large active volume and that mixed ionic and electronic transport remain efficient. Fast, reversible operation requires short ion pathways and stable interfaces.
Stretchability brings another layer of constraint: the channel and its contacts must adhere to soft substrates, survive repeated tensile loading, and maintain percolated pathways for both ions and electrons. Conventional dense polymer films restrict ion motion and limit volumetric charging. Coarse porosity can ease transport but often reduces mechanical strength and uniformity of the electronic network.
Device architecture adds a further constraint. Most soft circuits combine commodity polymers and metals in bonded stacks that are not intended for disassembly, which makes recovery of functional materials difficult once performance degrades. Any candidate platform for large area bioelectronics must therefore address three demands at once: strong ionic and electronic coupling with high transconductance, robustness under cyclic strain, and at least a partial route to materials recovery.
Fabrication and applications of organic electrochemical transistors (OECTs) based on PEDOT:PSS and PDPP-4T aerogels. a) Fabrication of OECTs based on nanoporous PEDOT:PSS aerogel films. b) Fabrication of OECTs based on nanoporous PDPP-4T aerogel films. c) Schematic of applications of semiconducting polymer aerogel-based OECT platforms in artificial synapse, biosensing, and tactile sensing. (Image: Reproduced with permission from Wiley-VCH Verlag) (click on image to enlarge)
The work uses two standard semiconducting polymers from organic electronics. One is PEDOT:PSS, where a positively charged PEDOT backbone is charge balanced by a negatively charged PSS polyanion. The other is PDPP-4T, a conjugated polymer based on diketopyrrolopyrrole and quaterthiophene units. Conjugation here refers to alternating single and double bonds that allow electronic charges to move along the chain.
To produce a PEDOT:PSS aerogel, the researchers mix the commercial dispersion with a silane crosslinker and co-dopants, cast this formulation into the channel region, and allow it to form a gel. They then exchange the solvent, dry the gel in conditions that preserve its pore network, and apply a thermal treatment. The result is a free-standing semiconducting aerogel film. For PDPP-4T, they first form an aerogel scaffold from polystyrene and styrene ethylene butylene styrene, then deposit the semiconducting polymer within this porous framework.
Structural characterization shows that both systems form continuous three-dimensional networks with pore sizes mainly in the 10–160 nm range and large specific surface areas. These pores are much smaller than the micrometer scale voids used in earlier macroporous films. The nanoporous architecture yields a dense interface between polymer and electrolyte and allows ions to access the bulk of the channel rather than only its outer surface.
When a PEDOT:PSS aerogel film acts as the channel in a stretchable organic electrochemical transistor on a soft styrene ethylene butylene styrene substrate, the electrical figures of merit change substantially compared with a dense film. The device reaches a transconductance of 27.4 mS, compared with the 0.23–3.7 mS range typical for many stretchable organic electrochemical transistors. The material exhibits a μC* value of 17.1 F cm⁻¹ V⁻¹ s⁻¹, where μ is electronic mobility and C* is volumetric capacitance.
A dense PEDOT:PSS film of similar thickness reaches only 0.16 F cm⁻¹ V⁻¹ s⁻¹. The areal capacitance rises from 1.8 mF cm⁻² to 5.5 mF cm⁻². Together these values indicate deeper ion penetration and more effective volumetric charging, which translate into stronger current modulation at a given gate bias.
Mechanical tests show that the aerogel channel maintains a continuous pathway under strain. Devices with PEDOT:PSS aerogel channels tolerate tensile strain up to 30 % without visible cracking. Under 30 % strain along the channel, the ON state drain current decreases by about 31 %, yet the devices continue to operate with high transconductance. After at least 3 000 cycles of stretching to 30 % and release, the transfer characteristics remain stable within modest drift.
Transistors based on PDPP-4T aerogels also operate at 30 % strain, although their ON current decays more during cycling. In both material systems, on and off switching over at least 1 000 electrical cycles confirms that the mixed ionic and electronic network survives repeated operation.
The aerogel platform is then evaluated in circuits that stress different aspects of device behavior, though the underlying physics remains the same. In neuromorphic tests, the aerogel transistor is driven by short voltage pulses at the gate. Each pulse injects and then withdraws ions from the channel, producing a transient current that rises and decays in a manner analogous to an excitatory post synaptic current.
The device shows pair pulse facilitation: when two pulses arrive in close succession, the second current peak exceeds the first, and this ratio decreases as the interval increases. These synaptic like responses persist up to 20 % strain, indicating that the ionic access and electronic percolation paths remain effective under deformation.
For chemical sensing, the same PEDOT:PSS aerogel channel is used in a stretchable uric acid sensor. The gate is modified with uricase, which catalyzes the oxidation of uric acid and generates reaction products that alter the local ionic environment. Through the electrolyte, this shift changes the doping state of the aerogel and thus the transistor current. Transfer curves shift systematically with uric acid concentration. Because the aerogel device combines high transconductance with high capacitance, these shifts produce clear current changes even at low analyte levels.
The sensor detects uric acid down to 1 nm and operates from 1 nm to 100 μm. That detection limit is about one to two orders of magnitude lower than many earlier organic electrochemical transistor based uric acid sensors, and the useful range covers concentrations relevant to sweat and wound exudate. The device maintains this behavior in artificial sweat and wound fluid and under 20 % strain.
In pressure sensing tests, a PEDOT:PSS aerogel channel is combined with an ionogel electrolyte made from a polymerized ionic liquid shaped into a regular array of micro pyramids. The effective contact area between the ionogel and the gate increases with applied pressure. At low pressure, only the pyramid tips contact the gate, limiting ion injection and keeping the channel more highly doped and conductive.
As pressure increases, the contact widens, more cations penetrate the aerogel, and the channel becomes less doped, which lowers the current. This contact controlled gating mechanism, together with the high transconductance of the aerogel transistor, yields a pressure response from 1 Pa to 5 000 Pa and a minimum detectable pressure of 0.5 Pa, including under 30 % tensile strain.
The study also examines end of life behavior. Immersing the complete device in n-hexane dissolves the styrene ethylene butylene styrene substrate, which can then be dried and reused as a film. The PEDOT:PSS aerogel becomes a wet gel but retains its integrity. After freeze drying, it returns to an aerogel with a preserved pore network. A new transistor built from this recycled aerogel on a fresh substrate reaches a peak transconductance of about 15.5 mS and still exhibits clear synaptic type responses under pulsed operation, while the film remains stretchable.
Overall, the work in Advanced Functional Materials identifies nanoporous semiconducting polymer aerogels as a practical channel architecture for soft organic electrochemical transistors. By replacing dense films with interconnected nanoscale pores, the devices achieve higher transconductance and capacitance, maintain mixed ionic and electronic transport under repeated strain, and allow partial recovery of both substrate and channel.
The same platform supports neuromorphic elements, chemical sensors, and pressure sensors, which indicates that engineering effort can focus on a single materials system while addressing mechanical and sustainability constraints central to biointegrated electronics.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
