Nanoscale doping of polymeric semiconductors with confined electrochemical ion implantation.

Nanoresolved doping of polymeric semiconductors can overcome scaling limitations to create highly integrated flexible electronics, but remains a fundamental challenge due to isotropic diffusion of the dopants. Here we report a general methodology for achieving nanoscale ion-implantation-like electrochemical doping of polymeric semiconductors. This approach involves confining counterion electromigration within a glassy electrolyte composed of room-temperature ionic liquids and high-glass-transition-temperature insulating polymers. By precisely adjusting the electrolyte glass transition temperature (Tg) and the operating temperature (T), we create a highly localized electric field distribution and achieve anisotropic ion migration that is nearly vertical to the nanotip electrodes. The confined doping produces an excellent resolution of 56 nm with a lateral-extended doping length down to as little as 9.3 nm. We reveal a universal exponential dependence of the doping resolution on the temperature difference (Tg - T) that can be used to depict the doping resolution for almost infinite polymeric semiconductors. Moreover, we demonstrate its implications in a range of polymer electronic devices, including a 200% performance-enhanced organic transistor and a lateral p-n diode with seamless junction widths of <100 nm. Combined with a further demonstration in the scalability of the nanoscale doping, this concept may open up new opportunities for polymer-based nanoelectronics.

Triggering ZT to 0.40 by Engineering Orientation in One Polymeric Semiconductor.

Breaking the thermoelectric (TE) trade-off relationship is an important task for maximizing the TE performance of polymeric semiconductors. Existing efforts have focused on designing high-mobility semiconductors and achieving ordered molecular doping, ignoring the critical role of the molecular orientation during TE conversion. Herein, the achievement of ZT to 0.40 is reported by fine-tuning the molecular orientation of one diketopyrrolopyrrole (DPP)-based polymer (DPP-BTz). Films with bimodal molecular orientation yield superior doping efficiency by increasing the lamellar spacing and achieve increased splitting between the Fermi energy and the transport energy to enhance the thermopower. These factors contribute to the simultaneous improvement in the Seebeck coefficient and electrical conductivity in an unexpected manner. Importantly, the bimodal film exhibits a maximum power factor of up to 346 µW m-1 K-2 , >400% higher than that of unimodal films. These results demonstrate the great potential of molecular orientation engineering in polymeric semiconductors for developing state-of-the-art organic TE (OTE) materials.

An Oligonucleotide-Distortion-Responsive Organic Transistor for Platinum-Drug-Induced DNA-Damage Detection.

Organic transistor with DNA-damage evaluation ability can open up novel opportunities for bioelectronic devices. Even though trace amounts of drugs can cause cumulative gene damage in vivo, the extremely low occurrence proportion makes them hardly transduced into detectable electric signals. Here, an ultrasensitive DNA-damage sensor based on an oligonucleotide-distortion-responsive organic transistor (DROT) is reported by creating controllable conformation change of double-stranded DNA on the surface of organic semiconductors. In combination with interfacial charge redistribution and efficient signal amplification, the DROT provides an ultrasensitive single-site DNA-damage response with 20.5 s even upon 1 × 10-12 m cisplatin. The high generalizability of this DROT to three generations of classical platinum drugs and gene-relevant DNA damage is demonstrated. A biochip is further designed for intelligent damage analysis in complex environments, which holds the potential for high-throughput biotoxicity evaluation and drug screening in the future.

Enhanced Thermoelectric Performance of n-Type Organic Semiconductor via Electric Field Modulated Photo-Thermoelectric Effect.

Modulating photophysical processes is a fundamental way for tuning performance of many organic devices. However, it has not been explored as an effective strategy to manipulate the thermoelectric (TE) conversion of organic semiconductors (OSCs) owing to their critical requirement to carrier concentration (>1018 cm-3 ) and the fact of low exciton separation efficiency in single element OSCs. Here, an electric field modulated photo-thermoelectric (P-TE) effect in an n-type OSC is demonstrated to realize a significant improvement of TE performance. The electrical and spectroscopy characterizations reveal that the electric field gating generates combined modulation of exciton separation, charge screening, and carrier recombination, which produces a more than ten times improvement of photoinduced carrier concentration. These coupled processes contribute to the unconventional Seebeck coefficient (S)-electrical conductivity (σ) trade-off relationship of the photoexcited films, therefore leading to a more than 500% enhancement in the power factor for n-type OTE semiconductors. This work opens a unique way toward state-of-the-art organic P-TE materials for energy harvesting applications.

Mimicking Sensory Adaptation with Dielectric Engineered Organic Transistors.

Mimicking sensory adaptation with transistors is essential for developing next-generation smart circuits. A key challenge is how to obtain controllable and reversible short-term signal decay while simultaneously maintaining long-term electrical stability. By introducing a buried dynamic-trapping interface within the dielectric layer, an organic adaptive transistor (OAT) with sensory adaptation functionality is developed. The device induces self-adaptive interfacial trapping to enable volatile shielding of the gating field, thereby leading to rapid and temporary carrier concentration decay in the conductive channel without diminishing the mobility upon a fixed voltage bias. More importantly, the device exhibits a fine-tuned decay constant ranging from 50 ms to 5 s, accurately matching the adaptation timescales in bio-systems. This not only suggests promising applications of OATs in flexible artificial intelligent elements, but also provides a strategy for engineering organic devices toward novel biomimetic functions.

Selenium-Substituted Diketopyrrolopyrrole Polymer for High-Performance p-Type Organic Thermoelectric Materials.

Development of high-performance organic thermoelectric (TE) materials is of vital importance for flexible power generation and solid-cooling applications. Demonstrated here is the significant enhancement in TE performance of selenium-substituted diketopyrrolopyrrole (DPP) derivatives. Along with strong intermolecular interactions and high Hall mobilities of 1.0-2.3 cm2 V-1 s-1 in doping-states for polymers, PDPPSe-12 exhibits a maximum power factor and ZT of up to 364 µW m-1 K-2 and 0.25, respectively. The performance is more than twice that of the sulfur-based DPP derivative and represents the highest value for p-type organic thermoelectric materials based on high-mobility polymers. These results reveal that selenium substitution can serve as a powerful strategy towards rationally designed thermoelectric polymers with state-of-the-art performances.

Excellent low-voltage operating flexible ferroelectric organic transistor nonvolatile memory with a sandwiching ultrathin ferroelectric film.

The high operating voltage is a primary issue preventing the commercial application of the ferroelectric organic field-effect transistor (Fe-OFET) nonvolatile memory (NVM). In this work, we propose a novel route to resolve this issue by employing two ultrathin AlOX interfacial layers sandwiching an ultrathin ferroelectric polymer film with a low coercive field, in the fabricated flexible Fe-OFET NVM. The operation voltage of Fe-OFET NVMs decreases with the downscaling thickness of the ferroelectric film. By inserting two ultrathin AlOX interfacial layers at both sides of the ultrathin ferroelectric film, not only the gate leakage is prominently depressed but also the mobility is greatly improved. Excellent memory performances, with large mobility of 1.7 ~ 3.3 cm2 V-1 s-1, high reliable memory switching endurance over 2700 cycles, high stable data storage retention capability over 8 × 104 s with memory on-off ratio larger than 102, are achieved at the low operating voltage of 4 V, which is the lowest value reported to data for all Fe-OFET NVMs. Simultaneously, outstanding mechanical fatigue property with the memory performances maintaining well over 7500 bending cycles at a bending radius of 5.5 mm is also achieved in our flexible FE-OFET NVM.

Achieving high mobility, low-voltage operating organic field-effect transistor nonvolatile memory by an ultraviolet-ozone treating ferroelectric terpolymer.

Poly(vinylidene fluoride-trifluoroethylene) has been widely used as a dielectric of the ferroelectric organic field-effect transistor (FE-OFET) nonvolatile memory (NVM). Some critical issues, including low mobility and high operation voltage, existed in these FE-OFET NVMs, should be resolved before considering to their commercial application. In this paper, we demonstrated low-voltage operating FE-OFET NVMs based on a ferroelectric terpolymer poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] owed to its low coercive field. By applying an ultraviolet-ozone (UVO) treatment to modify the surface of P(VDF-TrFE-CTFE) films, the growth model of the pentacene film was changed, which improved the pentacene grain size and the interface morphology of the pentacene/P(VDF-TrFE-CTFE). Thus, the mobility of the FE-OFET was significantly improved. As a result, a high performance FE-OFET NVM, with a high mobility of 0.8 cm2 V-1 s-1, large memory window of 15.4~19.2, good memory on/off ratio of 103, the reliable memory endurance over 100 cycles and stable memory retention ability, was achieved at a low operation voltage of ±15 V.