Chu-Chen Chueh

High performance nonvolatile transistor memories of pentacene using the electrets of star-branched p-type polymers and their donor–acceptor blends

Pentacene-based nonvolatile field-effect transistor (FET) memory utilizing novel electrets consisting of star-branched p-type polymers, polystyrene para-substituted oligofluorenes (P(StFl)n), and their hybrids with n-type PCBM was demonstrated in this work. As the arm number of P(StFl)n increases, the OFET hole mobility and memory window are improved to 0.69 cm2 V−1 s−1 and 19.75 V, with a high ON/OFF current ratio of over 108. The low dielectric constant of the large arm number of P(StFl)n leads to the greater loaded electric field and results in a large memory window. Moreover, the device performance can be further improved when the p-type star-branched (P(StFl)n) based electrets are blended with n-type PCBM. By precisely controlling the blended concentration of PCBM, the hole mobility of pentacene and the derived memory window could increase to 1.04 cm2 V−1 s−1 and 35.59 V, respectively. Two kinds of mechanism are proposed for P(StFl)n and PCBM:P(StFl)4 based memories, including carrier trapping and tunneling effect under a gate electric field. Our results not only show the potential of the star-branched polymers serving as electrets for FET memory, but also demonstrate the use of donor–acceptor (D–A) hybrid electrets is an efficient strategy to achieve high-performance nonvolatile OFET memories.

Multilevel nonvolatile flexible organic field-effect transistor memories employing polyimide electrets with different charge-transfer effects.

The electrical memory characteristics of the n-channel organic field-effect transistors (OFETs) employing diverse polyimide (PI) electrets are reported. The synthesized PIs comprise identical electron donor and three different building blocks with gradually increasing electron-accepting ability. The distinct charge-transfer capabilities of these PIs result in varied type of memory behaviors from the write-one-read-many (WORM) to flash type. Finally, a prominent flexible WORM-type transistor memory is demonstrated and shows not only promising write-many-read-many (WMRM) multilevel data storage but also excellent mechanical and retention stability.

Nonvolatile Perovskite‐Based Photomemory with a Multilevel Memory Behavior

Solution-processable organic-inorganic hybrid perovskite materials with a wealth of exotic semiconducting properties have appeared as the promising front-runners for next-generation electronic devices. Further, regarding its well photoresponsibility, various perovskite-based photosensing devices are prosperously developed in recent years. However, most exploited devices to date only transiently transduce the optical signals into electrical circuits while under illumination, which necessitates using additional converters to further store the output signals for recording the occurrence of light stimulation. Herein, a nonvolatile perovskite-based floating-gate photomemory with a multilevel memory behavior is demonstrated, for which a floating gate comprising a polymer matrix impregnated with perovskite nanoparticles is employed. Owing to the well photoresponsibility introduced by the embedded nanoparticles, the device is enabled to access multiple wavelength response and the functionalities of recording power/time-dependent illumination under no vertical electrical field. Intriguingly, a nonvolatility of photorecording exceeding three months with a high On/Off current ratio over 104 can be achieved.

Semi-conjugated acceptor-based polyimides as electrets for nonvolatile transistor memory devices

We report new polyimides as electrets for pentacene-based organic field-effect transistor (OFET) memory devices, consisting of different electron-accepting dianhydride moieties (PI(BPDA-DAP), PI(PMDA-DAP), and PI(ODPA-DAP)), and varied aliphatic spacer lengths (PI(PMDA-DAH) and PI(PMDA-DAD)). The effects of the molecular structures on the charge mobility and OFET memory characteristics were systematically investigated in terms of the related frontier energy levels and morphologies. All the devices showed bistable nonvolatile memory characteristics but with a distinct charge storage behavior. The OFET memory devices using the PI(BPDA-DAP) electret exhibited a larger memory window of 81 V compared to those of PI(PMDA-DAP) and PI(ODPA-DAP), mainly attributed to its low-lying LUMO energy level that results from its more extended conjugation. Both the high retention time (around 104 s for the ON/OFF states) and steady write-read-erase-read (WRER) cycles suggested good stability and read/write properties of the studied devices. As the aliphatic spacer length increased from PI(PMDA-DAP) to PI(PMDA-DAH) and PI(PMDA-DAD), the memory characteristics changed from flash to WORM (write once read many times) behaviour. Furthermore, the memory window was reduced with the increased aliphatic spacer length, due to the reduced density of the conjugated electron-trapping sites. This study demonstrated that the electrical characteristics and charge mobility of transistor memory devices can be effectively modulated through the extent of conjugation of the electron accepting moiety and spacer length in polymer electrets.

Uniform Luminous Perovskite Nanofibers with Color‐Tunability and Improved Stability Prepared by One‐Step Core/Shell Electrospinning

A one-step core/shell electrospinning technique is exploited to fabricate uniform luminous perovskite-based nanofibers, wherein the perovskite and the polymer are respectively employed in the core and the outer shell. Such a coaxial electrospinning technique enables the in situ formation of perovskite nanocrystals, exempting the needs of presynthesis of perovskite quantum dots or post-treatments. It is demonstrated that not only the luminous electrospun nanofibers can possess color-tunability by simply tuning the perovskite composition, but also the grain size of the formed perovskite nanocrystals is largely affected by the perovskite precursor stoichiometry and the polymer solution concentration. Consequently, the optimized perovskite electrospun nanofiber yields a high photoluminescence quantum yield of 30.9%, significantly surpassing the value of its thin-film counterpart. Moreover, owing to the hydrophobic characteristic of shell polymer, the prepared perovskite nanofiber is endowed with a high resistance to air and water. Its photoluminescence intensity remains constant while stored under ambient environment with a relative humidity of 85% over a month and retains intensity higher than 50% of its initial intensity while immersed in water for 48 h. More intriguingly, a white light-emitting perovskite-based nanofiber is successfully fabricated by pairing the orange light-emitting compositional perovskite with a blue light-emitting conjugated polymer.

A stable, efficient textile-based flexible perovskite solar cell with improved washable and deployable capabilities for wearable device applications

Organic–inorganic hybrid perovskite solar cells (PVSC) have appeared as promising high power-per-weight power systems for wearable electronic devices. Herein, we utilized a low-temperature electrodeposited tin oxide (SnO2) electron-transporting layer (ETL) coupled with a thin PCBM ETL and a functional encapsulating layer to realize an efficient, stable textile-based flexible PVSC. We first demonstrated that an easily accessible elastomer can serve as an effective encapsulating material for the fabricated flexible PVSC, as exemplified by the largely improved ambient stability and waterproof properties. Furthermore, we established that the good adhesive properties generated by the elastomer can largely enrich the deployable capability of the completed device stack as evidenced by the effortless integration of a completed device stack onto a textile. As a result, a ∼15% textile-based flexible PVSC with improved ambient stability and washable capability was demonstrated. A proof-of-concept device was successfully integrated with other electronic devices on a unitary textile to serve as an efficient power supply system for wearable electronic devices. The findings revealed in this work can promote the future potential applications of PVSCs in wearable device applications.

Bio-Based Transparent Conductive Film Consisting of Polyethylene Furanoate and Silver Nanowires for Flexible Optoelectronic Devices

Exploiting biomass has raised great interest as an alternative to the fossil resources for environmental protection. In this respect, polyethylene furanoate (PEF), one of the bio-based polyesters, thus reveals a great potential to replace the commonly used polyethylene terephthalate (PET) on account of its better mechanical, gas barrier, and thermal properties. Herein, a bio-based, flexible, conductive film is successfully developed by coupling a PEF plastic substrate with silver nanowires (Ag NWs). Besides the appealing advantage of renewable biomass, PEF also exhibits a good transparency around 90% in the visible wavelength range, and its constituent polar furan moiety is revealed to enable an intense interaction with Ag NWs to largely enhance the adhesion of Ag NWs grown above, as exemplified by the superior bending and peeling durability than the currently prevailing PET substrate. Finally, the efficiency of conductive PEF/Ag NWs film in fabricating efficient flexible organic thin-film transistor and organic photovoltaic (OPV) is demonstrated. The OPV device achieves a power conversion efficiency of 6.7%, which is superior to the device based on ITO/PEN device, manifesting the promising merit of the bio-based PEF for flexible electronic applications.

High-performance ternary polymer solar cells using wide-bandgap biaxially extended octithiophene-based conjugated polymers

Ternary organic photovoltaics (OPVs) have recently attracted intense research attention since they have been proven as an effective approach to enhance device performance. We herein describe a new strategy to realize high-performance ternary OPVs by using biaxially extended octithiophene (8T)-based wide-bandgap (Eg) conjugated polymers as the third photoactive component. Owing to the π–π transition of the biaxially extended conjugated side-chains, such polymers exhibit intense absorption in the near-ultraviolet region, in addition to the original intra-charge transfer (ICT) feature arising from the main backbone, revealing a new molecular design for wide-Eg polymers. By further tailoring the polymer backbone with p-type moieties such as thiophene (T) or thienothiphene (TT), two wide-Eg (∼2.0 eV) polymers, P8TT and P8TTT, with absorption wavelengths below 650 nm, were prepared, showing high complementary absorption to the spectra of both the state-of-the-art fullerene-(PTB7-Th:PC71BM) and non-fullerene-based (PBDB-T:ITIC) bulk-heterojunction (BHJ) systems. By providing suitable energy levels, P8TTT was demonstrated to enhance the power conversion efficiency (PCE) of its derived fullerene- and non-fullerene-based ternary blends by 7.58% and 6.60%, respectively, with only a small loading amount (10 wt%). This study manifests a new perspective in wide-Eg material design for realizing efficient ternary BHJ systems.

Multi-state memristive behavior in a light-emitting electrochemical cell

Carbohydrate-based block copolymers, such as maltoheptaose-block-polyisoprene (MHPI), were successfully employed as polyelectrolytes in a light-emitting electrochemical cell (LEC) to realize organic multi-state electrical memory. The observation of distinctive multi-state memristive behavior could be attributed to the controlled ion motion in MHPI and the electron capture capabilities introduced by its constituent hydroxyl groups. The newly developed sandwich-structured memory device is based on a LEC platform as the light-emitting electrochemical cell memory (LECM). Furthermore, the fabricated LECM exhibited excellent ternary-state memory behavior with high ON2/ON1/OFF current ratios of 106/105/1 as well as excellent stabilities for each respective state. The study not only illustrates the use of carbohydrate-based materials as promising electrolytes for LECM applications, but also provides a new horizon in the development of organic multi-state electrical memory devices.

Advances and Challenges of Green Materials for Electronic and Energy Storage Applications: From Design to End-of-Life Recovery

Harnessing biomass to fabricate electronic devices has lately drawn significant research attention because it not only represents a promising strategy for making materials but is also beneficial for the sustainable development of technologies. Numerous recent studies have demonstrated that green materials are promising candidates for synthesizing high-performance materials, such as biopolymers and hierarchical porous carbons. To catch up with this emerging tide, we have here compiled a comprehensive overview of state-of-the-art green materials, with a specific emphasis on recent progress in biodegradable polymeric materials and biomass-based carbon materials, together with their electronics and energy storage applications. Besides, we also assess the performance of end-of-life electronics recycling to highlight the merits of integrating green design with resource recovery.