Organic heterojunction synaptic device with ultra high recognition rate for neuromorphic computing

Traditional computing structures are blocked by the von Neumann bottleneck,and neuromorphic computing devices inspired by the human brain which integrate storage and computation have received more and more attention.Here,a flexible organic device with 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene(C8-BTBT)and 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene(C10-DNTT)heterostructural channel having excellent synaptic behaviors was fabricated on muscovite(MICA)substrate,which has a memory window greater than 20 V.This device shows better electrical characteristics than organic field effect transistors with single organic semiconductor channel.Furthermore,the device simulates organism synaptic behaviors successfully,such as paired-pulse facilitation(PPF),long-term potentiation/depression(LTP/LTD)process,and transition from short-term memory(STM)to long-term memory(LTM)by optical and electrical modulations.Importantly,the neuromorphic computing function was verified using the Modified National Institute of Standards and Technology(MNIST)pattern recognition,with a recognition rate nearly 100%without noise.This research proposes a flexible organic heterojunction with the ultra-high recognition rate in MNIST pattern recognition and provides the possibility for future flexible wearable neuromorphic computing devices.

Air-stable ambipolar organic field effect transistors with heterojunction of pentacene and N,N'-bis(4-trifluoromethylben-zyl) perylene-3,4,9,10-tetracarboxylic diimide

Fabrication of ambipolar organic field-effect transistors （OFETs） is essential for the achievement of an organic complementary logic circuit. Ambipolar transports in OFETs with heterojunction structures are realized.We select pentacene as a P-type material and N,N＇-bis（4-trifluoromethylben-zyl）perylene-3,4,9,10-tetracarboxylic diimide （PTCDI-TFB） as a n-type material in the active layer of the OFETs.The field-effect transistor shows highly air-stable ambipolar characteristics with a field-effect hole mobility of 0.18 cm^2/（V·s） and field-effect electron mobility of 0.031 cm^2/（V·s）.Furthermore the mobility only slightly decreases after being exposed to air and remains stable even for exposure to air for more than 60 days.The high electron affinity of PTCDI-TFB and the octadecyltrichlorosilane （OTS） self-assembly monolayer between the SiO2 gate dielectric and the organic active layer result in the observed air-stable characteristics of OFETs with high mobility.The results demonstrate that using the OTS as a modified gate insulator layer and using high electron affinity semiconductor materials are two effective methods to fabricate OFETs with air-stable characteristics and high mobility.

Simulation study of the losses and influences of geminate and bimolecular recombination on the performances of bulk heterojunction organic solar cells

We use the method of device simulation to study the losses and influences of geminate and bimolecular recombinations on the performances and properties of the bulk heterojunction organic solar cells. We find that a fraction of electrons（holes）in the device are collected by anode（cathode）. The direction of the corresponding current is opposite to the direction of photocurrent. And the current density increases with the bias increasing but decreases as bimolecular recombination（BR）or geminate recombination（GR） intensity increases. The maximum power, short circuit current, and fill factor display a stronger dependence on GR than on BR. While the influences of GR and BR on open circuit voltage are about the same.Our studies shed a new light on the loss mechanism and may provide a new way of improving the efficiency of bulk heterojunction organic solar cells.

Effect of Crystallinity of Fullerene Derivatives on Doping Density in the Organic Bulk Heterojunction Layer in Polymer Solar Cells

Polymer solar cells （PSCs） based on poly（3-hexylthiophene） （P3HT） and [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） are fabricated by using 1,8-diiodooctane （DIO） as a solvent additive to control the doping density of the PSCs. It is shown that the processing of DIO does not change the doping density of the P3HT phase, while it causes a dramatic reduction of the doping density of the PCBM phase, which decreases the doping density of the whole blend layer from 3.7 × 10^16 cm-3 to 1.2 ×10^16 cm-3. The reduction of the doping density in the PCBM phase originates from the increasing crystallinity of PCBM with DIO addition, and it leads to a decreasing doping density in the blend film and improves the short circuit current of the PSCs.

Tandem white organic light-emitting diodes adopting a C_(60) :rubrene charge generation layer

Organic bulk heterojunction fullerence(C60) doped 5, 6, 11, 12-tetraphenylnaphthacene(rubrene) as the high quality charge generation layer(CGL) with high transparency and superior charge generating capability for tandem organic light emitting diodes(OLEDs) is developed. This CGL shows excellent optical transparency about 90%, which can reduce the optical interference effect formed in tandem OLEDs. There is a stable white light emission including 468 nm and 500 nm peaks from the blue emitting layer and 620 nm peak from the red emitting layer in tandem white OLEDs. A high efficiency of about 17.4 cd/A and CIE coordinates of(0.40, 0.35) at 100 cd/m2 and(0.36, 0.34) at 1000 cd/m2 have been demonstrated by employing the developed CGL, respectively.

Enhanced Emission of Molybdenum Disulfide by Organic−Inorganic Hybrid Heterojunctions

Due to their excellent stability and layer-dependent photoelectronic properties,transition metal dichalcogenides(TMDs)are one of the most extensively studied two-dimensional semiconductor materials in the postgraphene era.However,its low luminescence quantum yield limits its application in displays,lighting,and imaging.Here,a 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile(HATCN)layer was grown on the surface of chemical vapor deposition(CVD)-grown monolayer molybdenum disulfide(MoS_(2))by vacuum evaporation,which increased the photoluminescence intensity of MoS_(2)by 15 times.The enhanced luminescence originates from the charge transfer from the conduction band of MoS_(2)to the lowest unoccupied molecular orbital(LUMO)of HATCN,which suppresses the emission of the negatively charged exciton(trion)while increasing the emission of the neutral exciton.Temperature-dependent fluorescence and Raman spectra demonstrate the feasibility of organic−inorganic hybrid heterojunctions for regulating excitons.This facile and practical organic−inorganic hybrid heterojunction can elevate TMD applications,such as light-emitting diodes.

Photocatalytic degradation of tetracycline hydrochloride with visible light-responsive bismuth tungstate/conjugated microporous polymer

Conjugated microporous polymer(CMP)is an emerging organic semiconductor withπ-conjugated skeletons,and the bandgap of CMP can be flexibly modulated to harvest visible light.Based on the diversity and adjustability of monomers in CMP,we designed and synthesized donor-accepter(D-A)type BTNCMP through Sonogashira-Hagihara cross-coupling polymerization,further in-situ constructing series of inorganic/organic Z-scheme BW/BTN-n composite in the presence of Bi_(2)WO_(6).After optimization,the tetracycline hydrochloride(C0=10 mg·L^(-1))degradation efficiency reached 84%with BW/BTN-2 as catalyst in 90 min under visible light irradiation,the apparent rate constant k1 is 0.017 min^(-1),which is 1.7 and 5.7 times higher than bare Bi_(2)WO_(6) and BTN-CMP.X-ray photoelectron spectra and UV-Vis diffuse spectra showed that the enhanced photocatalytic activity originated from the tight heterojunction between Bi_(2)WO_(6) and BTN-CMP,which can extend the light absorption range and facilitate the separation and transport of photogenerated charges in the interface of heterojunction.The active species trapping experiments and electron spin resonance technique revealed that h+was the dominant active species during the photodegradation process of tetracycline hydrochloride(TCH).The present study demonstrated the feasibility to construct inorganic/organic composite for the photocatalytic degradation of environmental pollutants.

Few-layered organic single-crystalline heterojunctions for high-performance phototransistors

Photogating and electrical gating are key physical mechanisms in organic phototransistors(OPTs).However,most OPTs are based on thick and polycrystalline films,which leads to substantially low efficiency of both photogating and electrical gating and thus reduced photoresponse.Herein,high-performance OPTs based on few-layered organic single-crystalline heterojunctions are proposed and the obstacle of thick and polycrystalline films for photodetection is overcome.Because of the molecular scale thickness of the type I organic single-crystalline heterojunctions in OPTs,both photogating and electrical gating are highly efficient.By synergy of efficient photogating and electrical gating,key figures of merit of OPTs reach the highest among those based on planar heterojunctions so far as we know.The production of few-layered organic single-crystalline heterojunctions will provide a new type of advanced materials for various applications.

Synthesis and Properties of Polythiophene Benzylidene and Their Photovoltaic Applications

Research on organic solar cells has a craze importance because they show very interesting properties including their flexibility and the opportunity to be made into large surfaces. However, their stability and performance should be significantly improved compared to their current state. A nominal output of around 10% will be the goal for the coming years. The use of organic materials for photovoltaic applications is the subject of intense research in recent years. This work is based in part on the development of new conjugated polymers. In this paper, we present the synthesis and characterization of poly [(thiophene-2,5-diyl)-co-(benzylidene)] PTB catalysed by Maghnite-H+, used in the active layer of the solar cell organic heterojunction with PCBM (derivative of C60) was used as a junction of the solar cell: Glas/ITO/BCP/C60/PTB/Au/Al. A current density of short circuit of about Jcc 0.1mA/cm2 was obtained for this structure with a yield of around 0.15%.

Influence of donor:acceptor ratio on charge transfer dynamics in non-fullerene organic bulk heterojunctions

The donor:acceptor(D:A) blend ratio plays a very important role in affecting the progress of charge transfer and energy transfer in bulk heterojunction(BHJ) orga nic solar cells(OSCs).The proper D:A blend ratio can provide maximized D/A interfacial area for exciton dissociation and appro p riate domain size of the exciton diffusion length,which is beneficial to obtain high-performance OSCs.Here,we comprehensively investigated the relationship between various D:A blend ratios and the charge transfer and energy transfer mechanisms in OSCs based on PBDB-T and non-fullerene acceptor IT-M.Based on various D:A blend ratios,it was found that the ratio of components is a key factor to suppress the formation of triplet states and recombination energy losses.Rational D:A blend ratios can provide appropriate donor/accepter surface for charge transfer which has been powerfully verified by various detailed experimental results from the time-resolved fluorescence measurement and transient absorption(TA) spectroscopy.Optimized coherence length and crystallinity are verified by grazing incident wide-angle X-ray scattering(GIWAXS) measurements.The results are bene ficial to comprehend the effects of various D:A blend ratios on charge transfer and energy transfer dynamics and provides constructive suggestions for rationally designing new materials and feedback for photovoltaic performance optimization in non-fullerene OSCs.

Band alignment and interlayer hybridization in monolayer organic/WSe_(2) heterojunction

Semiconducting heterojunctions(HJs),comprised of atomically thin transition metal dichalcogenides(TMDs),have shown great potentials in electronic and optoelectronic applications.Organic/TMD hybrid bilayers hold enhanced pumping efficiency of interfacial excitons,tunable electronic structures and optical properties,and other superior advantages to these inorganic HJs.Here,we report a direct probe of the interfacial electronic structures of a crystalline monolayer(ML)perylene-3,4,9,10-tetracarboxylic-dianhydride(PTCDA)/ML-WSe_(2) HJ using scanning tunneling microscopy,photoluminescence,and first-principle calculations.Strong PTCDAAA/Se_(2) interfacial interactions lead to appreciable hybridization of the WSe_(2) conduction band with PTCDA unoccupied states,accompanying with a significant amount of PTCDA-to-WSe_(2) charge transfer(by 0.06 e/PTCDA).A type-ll band alignment was directly determined with a valence band offset of-1.69 eV,and an apparent conduction band offset of-1.57 eV.Moreover,we found that the local stacking geometry at the HJ interface differentiates the hybridized interfacial states.

Organic–inorganic Au/PVP/ZnO/Si/Al semiconductor heterojunction characteristics

The paper reports the fabrication and characterization of a novel Au/PVP/ZnO/Si/Al semiconductor heterojunction（HJ） diode. Both inorganic n type ZnO and organic polyvinyl pyrrolidone（PVP） layers have grown by sol-gel spin-coating route at 2000 rpm. The front and back metallic contacts are thermally evaporated in a vacuum at pressure of 10^-6 Torr having a diameter of 1.5 mm and a thickness of 250 nm. The detailed analysis of the forward and reverse bias current-voltage characteristics has been provided. Consequently, many electronic parameters, such as ideality factor, rectification coefficient, carrier concentration, series resistance, are then extracted.Based upon our results a non-ideal diode behavior is revealed and ideality factor exceeds the unity（n 〉 4）. A high rectifying（-4.6 × 10^4） device is demonstrated. According to Cheung-Cheung and Norde calculation models, the barrier height and series resitance are respectively of 0.57 eV and 30 kΩ. Ohmic and space charge limited current（SCLC） conduction mechanisms are demonstrated. Such devices will find applications as solar cell, photodiode and photoconductor.

碳量子点/四(4-羧基苯基)卟啉/BiOBr S型异质结用于高效光催化降解抗生素

太阳能光催化处理制药废水是缓解环境问题和能源危机的一种很有前途的方法.然而,提高其处理效率面临众多挑战,如光吸收效率低、光生载流子快速复合和光氧化还原电位低等.本文通过在BiOBr(BOB)微球上沉积碳量子点(CDs)和四(4-羧基苯基)卟啉(TCPP),巧妙地构建了TCPP/CDs/BOB有机/无机三元S型异质结,用于在可见光下有效降解水体中的盐酸四环素(TC).研究发现,由于两者之间的费米能级差异,在形成异质结时触发了电子从TCPP传递到BOB,从而在界面处构建内部电场(IEF).这极大推动了光诱导载流子的有效分离.此外,CDs作为电子收集器进一步提高了S型异质结的载流子分离能力,因此保留了在CDs中聚集更强还原能力的光电子和在BOB价带中更强氧化能力的空穴来参与光催化反应.在这些催化剂中,TCPP/CDs/BOB-2异质结催化剂在40 min内对TC的降解能力高达83.6%.TCPP/CDs/BOB-2的反应速率常数(k)分别约为BOB、CDs/BOB和TCPP/BOB的2.3、1.8和2.0倍.这项工作为探索用于水净化的有机/无机三元S型光催化剂提供了新的视角.

Low-voltage-modulated perovskite/organic dual-band photodetectors for visible and near-infrared imaging

Visible and near-infrared(NIR)light dual-band photodetectors(PDs)have potential applications in signal detection,bioimaging,optical communications and safety monitoring.Herein,we report an ultrafast perovskite/organic heterojunction dual-mode PD with a voltage-modulated photoresponse range in visible and NIR spectra.The PD,comprising a perovskite layer to absorb visible light(500–810 nm)and an organic bulk heterojunction layer for NIR light absorption(810–950 nm),exhibited a switchable spectral response in the visible or NIR bands.The voltage-modulated visible and NIR photoresponses of the PD were attributable to controlled charge photogeneration in perovskite and organic blend thin films under different bias polarities.The device exhibited peak responsivities of 93.5 and 102.2 mA/W in the visible and NIR bands,respectively;a high detectivity of 4.3×10^(9) Jones(at forward bias of 0.7 V and incident 625 nm light)and 1.6×10^(12) Jones(at reverse bias of–1.5 V and incident 900 nm light);a fast microsecond response time;and a wide dynamic range(>120 dB)both in the visible mode and NIR mode.Also,this voltage-modulated dual-band PD shows promising applications in visible light and NIR imaging,which is proven by demonstrating a PD array with 25 pixels(5×5).

Novel broad spectral response perovskite solar cells:A review of the current status and advanced strategies for breaking the theoretical limit efficiency

Perovskite solar cells(PSCs)have revolutionized photovoltaic research.The power conversion efficiency(PCE)of PSCs has now reached 25.7%,which is comparable to current state-of-the-art silicon-based cells.However,PSCs can only utilize light of 300-850 nm,resulting in wasted near-infrared(NIR)light,which occupies 45%-50%of entire solar spectrum,which is one of the main reasons limiting the development of efficiency.Related strategies to broaden NIR spectroscopy to break the theoretical limit efficiency of PSCs have recently attracted extensive attention.This review firstly outlines theoretical basis for improving the NIR spectroscopy,then systematically summarizes some key strategies and research progress to improve NIR spectroscopy of PSCs.We firstly provided a comprehensive overview of historical research experiments on narrow-gap perovskite absorber layers,rare earth up-conversion,tandem devices,and integrated perovskite/organic solar cells and given constructive suggestions for exceeding limit efficiency of PSCs.Finally,based on the development status of PSCs with NIR utilization,the current issues,solutions and future development directions of important aspects to improve NIR utilization of PSCs are systematically discussed.This review lays the foundation for the efficiency of PSCs beyond the Shockley-Queisser limit,and provides a certain development prospect.

Conjugated Polymers as Hole Transporting Materials for Solar Cells

In principle,conjugated polymers can work as electron donors and thus as low-cost p-type organic semiconductors to transport holes in photovoltaic devices.With the booming interests in high-efficiency and low-cost solar cells to tackle global climate change and energy shortage,hole transporting materials(HTMs)based on conjugated polymers have received increasing attention in the past decade.In this perspective,recent advances in HTMs for a range of photovoltaic devices including dye-sensitized solar cells(DSSCs),perovskite solar cells(PSCs),and silicon(Si)/organic heterojunction solar cells(HSCs)are summarized and perspectives on their future development are also presented.