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A spiking neural network consists of artificial synapses and neurons and may realize human-level intelligence. Unlike the widely reported artificial synapses, the fabrication of large-scale artificial neurons with good performance is still challenging due to the lack of a suitable material system and integration method. Here, we report an ultrathin (less than10 nm) and inch-size two-dimensional (2D) oxide-based artificial neuron system produced by a controllable assembly of solution-processed 2D monolayer TiOx nanosheets. Artificial neuron devices based on such 2D TiOx films show a high on/off ratio of 109 and a volatile resistance switching phenomenon. The devices can not only emulate the leaky integrate-and-fire activity but also self-recover without additional circuits for sensing and reset. Moreover, the artificial neuron arrays are fabricated and exhibited good uniformity, indicating their large-area integration potential. Our results offer a strategy for fabricating large-scale and ultrathin 2D material-based artificial neurons and 2D spiking neural networks.

Magnetically influenced light-matter interaction provides a contactless, noninvasive and power-free way for material characterization and light modulation. Shape anisotropy of active materials mainly determines the sensitivity of magneto-optic response, thereby making magnetic two-dimensional (2D) materials suitable in achieving the giant magneto-birefringence effect as discovered recently. Consequently, relationship between magneto-birefringence response and shape anisotropy of 2D materials is critical but has remained elusive, restricting its widespread applications. Here, we report the highly sensitive and largely tunable magneto-coloration via manipulating the shape-anisotropy of magnetic 2D materials. We reveal a quadratic increasing relationship between the magneto-optic Cotton-Mouton coefficient and the lateral size of 2D materials and achieve a more than one order of magnitude tunable response. This feature enables the engineerable transmissive magneto-coloration of 2D materials by tailoring their shape anisotropy. Our work deepens the understanding of the tunability of magneto-optic response by size effect of active materials, offering various opportunities for their applications in vast areas where color is concerned.

One of the long sought-after goals in manipulation of light through light-matter interactions is the realization of magnetic-field-tuneable colouration, so-called magneto-chromatic effect, which holds great promise for optical, biochemical and medical applications due to its contactless and non-invasive nature. This goal can be achieved by magnetic-field controlled birefringence, where colours are produced by the interference between phase-retarded components of transmitted polarised light. Thus far birefringence-tuneable coloration has been demonstrated using electric field, material chirality and mechanical strain but magnetic field control remained elusive due to either weak magneto-optical response of transparent media or low transmittance to visible light of magnetically responsive media, such as ferrofluids. Here we demonstrate magnetically tuneable colouration of aqueous suspensions of two-dimensional cobalt-doped titanium oxide which exhibit an anomalously large magneto-birefringence effect. The colour of the suspensions can be tuned over more than two wavelength cycles in the visible range by moderate magnetic fields below 0.8 T. We show that such giant magneto-chromatic response is due to particularly large phase retardation (>3 pi) of the polarised light, which in its turn is a combined result of a large Cotton-Mouton coefficient (three orders of magnitude larger than for known liquid crystals), relatively high saturation birefringence (delta n = 2 x 10^-4) and high transparency of our suspensions to visible light. The work opens a new avenue to achieve tuneable colouration through engineered magnetic birefringence and can readily be extended to other magnetic 2D nanocrystals. The demonstrated effect can be used in a variety of magneto-optical applications, including magnetic field sensors, wavelength-tuneable optical filters and see-through printing., 10 pages, 4 figures. Nature Communications, 2020, Accepted

A novel Ni 3 S 2 film, comprising interconnected nanoparticles, on Ni foam is synthesized by using a simple one-step hydrothermal approach. The Ni 3 S 2 film electrode exhibits excellent pseudocapacitor characteristics, 1) a huge specific capacitance up to 2230 F g −1 attained at a current density of 5 mA cm −2 , and 2) a nearly perfect retention rate of 91% at a current density of 10 mA cm −2 after 3000 cycles. These experimentally demonstrated that the special nanoparticle-interconnected structure in conjunction with the high-performance electrode characteristics, make the Ni 3 S 2 film electrode an attractive and competitive candidate for the development of advanced high-efficiency electrochemical energy storage devices.

Developing an organic luminescent solar concentrator (LSC), featuring ultralong lifetime and high transparency simultaneously, is crucial for building-integrated photovoltaic applications, such as solar energy harvesting clear windows. In this paper, a tandem organic LSC is encapsulated and connected with three optically transparent layers, namely an encapsulating epoxy layer and two insulating SiO2 layers that prevent dissolving the organic dyes into the epoxy layer. Experimental results demonstrate that the encapsulated organic LSC maintains the high average transmission of 60% in the visible range of 390–750 nm, and has an ultralong lifetime of $\sim 6.7 \times 10^{4}$ h under illuminated test in laboratory environment, which is around five times longer than that of the organic LSC without any encapsulation. In addition, experiments confirm that most of the photoluminescence radiation generated in the organic dyes is trapped in the high-index SiO2/epoxy/SiO2 structure, and guided between the glass substrate before emerging from the four edges of the organic LSC sample for conversion to electricity. A 30% increase in short-circuit current is attained, in comparison with a similar unencapsulated organic LSC structure.

In solar cells, a maximum external quantum efficiency of 100% can be attained if the photocurrent originates from the dissociation of singlet excitons. However, a higher efficiency can be attained through singlet fission (SF), where multiple charge carrier pairs are generated from a single photon, thus increasing the number of excitons and hence the photocurrent generation. The verification of SF is normally difficult and costly. In this study, SF is verified in pentacene by simply measuring the external quantum efficiency (EQE) of a device with a very thick pentacene (indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulphonate) (PEDOT:PSS) (40 nm)/pentacene (600 nm)/fullerene (40 nm)/tris-8-hydroxy-quinolinato aluminum (8 nm)/Al). A measured EQE of 6.16% at 695 nm is achieved, which is much larger than the maximum calculated EQE (3.45%). The calculation was based on the assumption that all singlet excitons (if SF did not occur) reaching the pentacene–C60 interface contribute to the photocurrent. To account for this discrepancy, only singlet fission to double the number of excitons can be supposed, since a longer singlet diffusion length of 140 nm is not practical in pentacene. Thus, SF in pentacene and the dissociation of triplet excitons at the pentacene–C60 interface have been verified.

Optical effects of the plasmonic structures and the materials effects of the metal nanomaterials have recently been individually studied for enhancing performance of organic solar cells (OSCs). Here, the effects of plasmonically induced carrier generation and enhanced carrier extraction of the carrier transport layer (i.e., plasmonic-electrical effects) in OSCs are investigated. Enhanced charge extraction in TiO2 as a highly efficient electron transport layer by the incorporation of metal nanoparticles (NPs) is proposed and demonstrated. Efficient device performance is demonstrated by using Au NPs incorporated TiO2 at a plasmonic wavelength (560–600 nm), which is far longer than the originally necessary UV light. By optimizing the concentration ratio of the Au NPs in the NP-TiO2 composite, the performances of OSCs with various polymer active layers are enhanced and efficiency of 8.74% is reached. An integrated optical and electrical model, which takes into account plasmonic-induced hot carrier tunneling probability and extraction barrier between TiO2 and the active layer, is introduced. The enhanced charge extraction under plasmonic illumination is attributed to the strong charge injection of plasmonically excited electrons from NPs into TiO2. The mechanism favors trap filling in TiO2, which can lower the effective energy barrier and facilitate carrier transport in OSCs.

Roles of the buried interface between polymer poly(3-hexylthiophene) (P3HT) layer and indium tin oxide (ITO) on the glass substrate have been characterized by transient photovoltage (TPV). Since P3HT is the hole-transporting material, from intuitiveness, ITO/P3HT contact (IPcontact) tends to be hole extracting. However, in this letter, the negative TPV of ITO/P3HT/Al demonstrates that IPcontact dominates the reversed built in electric field, namely pointing from ITO to Al, and is confirmed to be electron extracting. Meanwhile, an interesting biphasic feature of TPV is demonstrated in a device of ITO/P3HT:[6,6]-phenyl-C61-butyric acid methyl ester/Al. The negative component in biphasic TPV shows that IPcontact is one reason resulting in the leakage current for P3HT based solar cells in normal structures. The theoretical study is conducted, and reveals that the interaction between P3HT and ITO reduces electron barrier by 0.5 eV for IPcontact. Band bending and dipole formation are two possible reasons to reduce the electron barrier. By taking advantage of the electron extraction, IPcontact is employed as a composite cathode in an inverted solar cell by pre-coating a pristine P3HT buffer layer between a blended layer and ITO. The study paves a way to characterize the buried interface in solution processable optoelectronics by observing polarity change of TPV, and to fabricate the simplified inverted organic solar cell employing IPcontact to extract electrons.

We explore in this work the use of Cu as a cathode material in organic light-emitting devices (OLEDs) and find a dual electron–injection enhancement mechanism derived from the LiF layer. Different from what observed previously in Ag- and Au-cathode devices, the LiF buffer layer in the Cu-cathode OLEDs starts to play its role in performance improvement when it is much thinner than 3 nm, the optimal value of buffer thickness, and in the case of optimal thickness, the device exhibits excellent performance comparable to conventional Al-cathode device. The phenomenon observed is ascribed to enhanced electron injection as a result of combined effect of interfacial reaction and tunneling barrier reduction mechanism: while chemical reaction plays a key role at the very beginning of interface formation, tunneling dominates in the subsequent stage leading to the tremendous improvement of the characteristics.

Polymer-fullerene-based bulk heterojunction (BHJ) solar cells have many advantages, including low-cost, low-temperature fabrication, semi-transparency, and mechanical fl exibility. [ 1 , 2 ] However, there is a mismatch between optical absorption length and charge transport scale. [ 3 , 4 ] These factors lead to recombination losses, higher series resistances, and lower fi ll factors. Attempts to optimize both the optical and electrical properties of the photoactive layer in organic solar cells (OSCs) inevitably result in a demand to develop a device architecture that can enable effi cient optical absorption in fi lms thinner than the optical absorption length. [ 5 , 6 ] Here, we report the use of two metallic nanostructures to achieve broad light absorption enhancement, increased shortcircuit current ( J sc ), and improved fi ll factor ( FF ) simultaneously based on the new small-bandgap polymer donor poly{[4,8-bis(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b ′ ]dithiophene2,6-diyl]alt -[2-(2 ′ -ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl]} (PBDTTT-C-T) in BHJ cells. [ 7 ] The dual metallic nanostructure consists of a metallic nanograting electrode as the back refl ector and metallic nanoparticles (NPs) embedded in the active layer. Consequently, we achieve the high power conversion effi ciency (PCE) of 8.79% for a single-junction BHJ OSC. Recently, plasmonic nanostructures have been introduced into solar cells for highly effi cient light harvesting. [ 5 , 8–17 ] Two types of plasmonic resonances, surface plasmonic resonances (SPRs) [ 18–22 ] and localized plasmonic resonances (LPRs), [ 11–14 ] can be used for enhancing light absorption. Metallic gratingbased light-trapping schemes have been investigated in traditional inorganic photovoltaic cells. [ 18–20 ] For metallic nanogratings, which can support SPRs, it is still challenging to experimentally demonstrate the enhancement of PCE in OSCs owing to the obvious issue of solution processing of

Au is not a suitable cathode material of organic light-emitting device because of its high work function resulting in poor electron injection. However, in present work, it is found that the performance of Au-cathode OLEDs can be efficiently improved by introducing a LiF buffer layer and with its optimal thickness can even be comparable to that of conventional Al-cathode device. The relationship between the thickness of LiF layer and the performance improvement is investigated. The experimental results indicate a quite different mechanism of LiF thin layer from that of Al-cathode device, which is not chemical-reaction-mechanism-dominant. Other insulator material buffer layers such as Al2O3 and BCP are also investigated.

The effect of voltage exceeding Vmin, the voltage corresponding to the local current minimum, on organic bistable devices is investigated. It is found that when the termination voltage VT exceeds Vmin, with the increasing VT, the bistable effect gets worse and finally lost at VT about 2Vmin. However, the bistable effect can be recovered by applying a voltage pulse with amplitude near Vmin for milliseconds or longer. The existence of localized conducting micro-channels is suggested to account for the bistable effect.

By adopting C60/Al composite anode and an inverted device structure of ITO/Alq3/C60/CuPc/C60/Al, we have achieved a power conversion efficiency of 0.78% under 75 mW/cm2 AM1.5G simulated illumination and a shelf lifetime of 950 h from unencapsulated organic solar cells. The improved stability is attributed to efficient protection of the C60 layer in the inverted structure. Replacing the C60/Al anode with C60/Au anode in the inverted structure, produces a power conversion efficiency of 0.64%, comparable to that of the device with C60/Al anode. This indicates that the property of the composite electrode is mainly determined by the thin C60 layer. Use of C60/Al composite anode to fabricate inverted organic light-emitting devices gives rise to an efficiency of the device comparable to that of conventional devices.

The role of ultra-thin buffer layer of C 60 in recently developed high contrast-ratio tandem organic light emitting devices (HCT-OLEDs) is experimentally investigated. The strong photon emission of Al/C 60 / N, N'-di(naphthalene-l-yl)- N, N'- diphenylbenzidine/tris8-hydroxyquinoline-aluminum/LiF/Al verifies the efficient hole-injecting role of Al (7 nm)/C 60 (2.5 nm). When the applied voltage is higher than 15 V, abrupt drop in current is experienced and the peak of the electroluminescence spectrum vanishes as a result of the phase tuning structure of the HCT-OLED. This demonstrates that the Al/C 60 anode performance is unstable under high voltage operation. Such instability causes HCT-OLED power efficiency to drop significantly, necessitating more stable buffer layers to be used instead of C 60 in order to realise viable HCT-OLEDs for display applications.

The impact of a LiF/Al/Au composite layer on both electrical performance and optical performance of high contrast-ratio tandem organic light emitting devices (HCT-OLEDs) operating in wide viewing angle regimes is investigated. The strong photon emission from Al/Au/ NPB(N,N′-di(naphthalene-1-yl)- N,N′-diphenylbenzidine) /Alq 3 (tris8-hydroxyquinoline-aluminum)/LiF/Al and the symmetrical current-voltage curve for Al/LiF/Alq 3 /LiF/Al verify the hole-injecting anodic and the electron-injecting cathodic roles of Al(4 nm)/Au(7 nm) and Al(4 nm)/LiF(0.7 nm), respectively. The reflectivity spectrum is measured for viewing angles ranging from 5° to 50°. Experimental results show that when the viewing angle is increased from 5° to 50°, the reflectivity spectrum is blue shifted, which affects the contrast of HCT-OLEDs. Importantly, the measured average reflectivity in the visible range for viewing angles below 50° is as low as 6.6%, making the proposed HCT-OLEDs attractive for flat-panel-display applications.

In this work, we investigate the effect of the thickness of the polyethylenimine ethoxylated (PEIE) interface layer on the performance of two types of polymer solar cells based on inverted poly(3-hexylthiophene) (P3HT):phenyl C61-butryric acid methyl ester (PCBM) and thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Maximum power conversion efficiencies of 4.18% and 7.40% were achieved at a 5.02 nm thick PEIE interface layer, for the above-mentioned solar cell types, respectively. The optimized PEIE layer provides a strong enough dipole for the best charge collection while maintaining charge tunneling ability. Optical transmittance and atomic force microscopy measurements indicate that all PEIE films have the same high transmittance and smooth surface morphology, ruling out the influence of the PEIE layer on these two parameters. The measured external quantum efficiencies for the devices with thick PEIE layers are quite similar to those of the optimized devices, indicating the poor charge collection ability of thick PEIE layers. The relatively low performance of devices with a PEIE layer of thickness less than 5 nm is the result of a weak dipole and partial coverage of the PEIE layer on ITO.

A self-assembled three-dimensional (3-D) MoS2 microsphere-based memristor with a favorable ON/OFF resistance ratio of ∼104, endurance, and retention time is demonstrated at room temperature. The formation and rupture of a localized Ag metallic filament, establishment and destruction of a boundary-based hopping path, and charge trapping and detrapping from the space charge region co-contribute to the bipolar resistive switching memory behaviours observed in the device of Ag/MoS2/ITO. This work may give insight into the mechanism of the resistive switching memory behaviours of a device with a 3-D micro-scale.

In this work, nonvolatile bipolar resistive switching behaviors based on the MoS2 quantum dots (QDs) embedded in the insulating polymethylmethacrylate (PMMA) were reported with the device configuration of Au/PMMA/PMMA:MoS2 QDs/PMMA/fluorine doped tin-oxide. The device exhibits the reversible switching performances with the excellent read endurance and data retention capability. The related carrier transport behaviors were predominated by Schottky emission and Ohmic conductions in OFF and ON states, respectively. Importantly, a conductance quantization effect was evidently observed in this MoS2 QD-based memory device. Combined with the energy band evolution, these phenomena were elucidated in views of electrons trapping/de-trapping and quantum tunneling effects of nanoscale MoS2 QDs. This work also suggests the potential application of MoS2 QDs in next generation ultra-high-density data storage.

MoSe2-doped ultralong Se microwires of length/diameter ratio in the order of ∼240 are synthesized by hydrothermal method. An electronic resistive switching memory (ERSM) device using a single MoSe2-doped ultralong Se microwire is attained. The ERSM exhibits stable resistance ratio of ∼102 for 5000 s, highly stable performance during 500 stressing cycles, and excellent immunity to the frequency of the driving voltage. By investigating the dynamic processes of trap filling, de-trapping, and free-charge migration, trap-controlled space-charge-limited current mechanism is found to dominate the observed ERSM behaviour.

A high contrast-ratio organic light emitting device (OLED) with an emissive phase tuning layer is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning layers between composite metal layers of LiF/Al/C 60 and LiF/Al and optimizing their thicknesses. Electroluminescence spectrum reveals that the phase tuning layer emits light due to the insertion of ultra-thin C 60 . Such a tandem device can reduce the operating voltage by 1.1 V, in comparison to conventional high contrast OLEDs. Measured reflection spectra validate the high-contrast capability of the OLED, and demonstrate experimentally an average reflectivity of 6.0% in the visible range from 400 nm to 750 nm, which is much lower than 20.3% for conventional high contrast OLED.

Conventional and inverted thin CdS/CdTe-based solar cells are fabricated using thermal deposition techniques, and their performance under an external electric field is investigated. Results show that both positive and negative electric fields can change the performance of the developed solar cells and that the latter recover to their initial state after switching the external electric field off. Heat treatment experiments confirm the negligible impact of the temperature on the solar cell performance. Transient photocurrent experiments show that the carrier transfer efficiency is modulated directly by an external electric field. By taking into account the CdS nanodipole, the effect of an external electric field on the solar cell performance can be well explained. The results presented in this paper open the way toward the realization of solar cells through carrier separation by an electric field provided by the CdS nanodipoles rather than the solar cell junction.

In this paper, we demonstrate the concept of a cost-effective, environment-friendly, highly stable, and efficient organic luminescent solar concentrator (OLSC) structure based on the use of an optically transparent lamination layer comprising a blend of an organic semiconductor host material and an organic red dye material, which is sandwiched between two glass panes. Experimental results demonstrate that the developed OLSC can achieve a power conversion efficiency of up to 5.3% and a lifetime of >1.0 × 105 h when operated in ambient environment. This is attributed to the enhanced solar light harvesting of the host materials, the ultra-low ultraviolet transmission, and negligible oxygen and water content permeability of the ultraviolet cured lamination layer. The high efficiency in conjunction with the cost-effective material selection contributes to the low cost per peak watt, making the reported OLSC structures attractive for building-integrated photovoltaic applications.

In this paper, we demonstrate the concept of a room-temperature spin-polarized organic light-emitting diode (Spin-OLED) structure based on (i) the deposition of an ultra-thin p-type organic buffer layer on the surface of the ferromagnetic electrode of the Spin-OLED and (ii) the use of oxygen plasma treatment to modify the surface of that electrode. Experimental results demonstrate that the brightness of the developed Spin-OLED can be increased by 110% and that a magneto-electroluminescence of 12% can be attained for a 150 mT in-plane magnetic field, at room temperature. This is attributed to enhanced hole and room-temperature spin-polarized injection from the ferromagnetic electrode, respectively.

A high contrast-ratio organic light emitting device (OLED) is proposed and experimentally demonstrated. The OLED is implemented by stacking two organic phase tuning (PT) layers between composite metal layers and optimizing their thicknesses. Such a tandem device can increase the current efficiency by 98%, and reduce the operating voltage by 1.04 V, in comparison to conventional high contrast OLEDs. Measured reflection spectra validate the high-contrast capability of the OLED, and demonstrate experimentally an average reflectivity of 6% under ambient light illumination. This is the lowest reflectivity reported to date for OLEDs employing organic phase tuning layers.

The biphasic feature of transient photo-generated voltage (TPV) is investigated in organic solar cells (OSCs) with a blend active layer of poly(3-hexylthiophene) (P3HT) and phenyl C61 butyric acid methyl ester (PCBM). The positive and negative components in biphasic TPV are explained through PCBM only and P3HT only devices. The negative and positive components are ascribed to the dipole formation at the buried interface of P3HT/indium tin oxide (ITO) and PCBM/ITO respectively. Based on these findings, two fundamental phenomena are revealed as follows: (1) interfacial modification on the buried interface inverts the negative component in biphasic TPV to a positive component, which prevents the leakage current channel in the conventional OSC structure; and (2) the solvent chosen transforms the positive component in biphasic TPV into a negative signal, which blocks the leakage current channel in the inverted OSC structure. Consequently, the study of TPV polarity provides the justification of the interaction at the buried interface. Besides, the decay of TPV is found to be bi-exponential, which can be used as a tool to estimate the degree of charge balance in OSCs.

The magnetoelectroluminescence (MEL) of organic light emitting devices with a N,N′-bis(l-naphthyl)-N,N′-diphenyl-1,l′-biphentl-4,4′-diamine:tris-(8-hydroxyquinoline) aluminum (NPB:Alq3) mixed emission layer (EML) has been investigated. We find that MEL is maximized when the volume ratio of NPB of the mixed EML reaches 30% and the EML thickness is 40 nm. The features of MEL under various magnetic field strengths are insensitive to the change in EML thickness and mixing ratio. Meanwhile, MEL has a close relationship with the carrier mobility. We have conducted a theoretical study to further verify the relationship. Our experimental and theoretical results confirm that MEL can function as a tool to indicate the mobility.

We present a time-dependent device model, describing the dynamical processes of both exciton induced by light illumination and charge carriers created from the exciton dissociation, to calculate the transient photovoltage (TPV) in single-layer organic photovoltaic cells. With reasonable parameters for the specific ITO (indium tin oxide)/CuPc (copper phthalocyanine)/Al (aluminum) structure, we could obtain the TPV well fitted with previous experimental observation by adjusting only the intensity of input laser pulse. Further, we saw a saturation of this TPV by changing the intensity of laser pulse from the calculation, which has been confirmed by the experimental measurement on ITO/NPB [N,N-bis(l-naphthyl)-N,N-diphenyl-1,l-biphentl-4,4-diamine]/Al structure. The saturated TPV value is found to be sensitive to the mobility of minority carriers, which might be useful in the estimation of mobilities.

Electroluminescence (EL) with brightness up to 300 cd/m(2) is observed from organic light-emitting diodes fabricated on oxygen-treated La(0.7)Sr(0.3)MnO(3) anodes. An external magnetic field of 150 mT applied parallel to the device surface can enhance the EL intensity by 10%, accompanied by a raised current efficiency. In-plane magnetization of the ferromagnetic anode is found to be the main origin of increase in the current contributable to EL, though magnetoresistance of the organic functional materials also plays a role in the EL enhancement observed in the magnetic field.

A p-type doped organic layer combined with a hole-blocking layer has been experimentally demonstrated to serve as the charge generation unit in tandem-type organic light-emitting devices. The p-type layer functions as the source of both holes and electrons. Charge separation is explained by the tunneling model that the hole-blocking layer reduces the energy barrier for the electrons generated in the p-type layer to tunnel through into one light-emitting unit, while the holes generated in the p-type layer can transport to the other light-emitting unit easily under operation voltage.

The dissociation of excitons at indium tin oxide (ITO)∕C60 interface is studied by means of transient photovoltage measurements. An abnormal polarity change of transient photovoltage from positive to negative upon pulsed laser irradiation is observed, indicating that the exciton dissociation at ITO∕C60 interface results in holes injected into ITO and electrons left in the C60 film, opposite to that occurring at ITO/NPB and ITO/CuPc interfaces. It is confirmed that C60 has a moderately strong ability of donating holes to ITO during the dissociation process of the excitons at the ITO∕C60 interface. Moreover the long term transient photovoltage (t>10ns) and its polarity can be tuned by applying external bias on the device, which further proves the validity of the model proposed to explain the polarity change of the transient photovoltage.

We report a delayed-switch-on effect in organic memories; i.e., the organic memory devices can automatically switch from off state to on state after a certain period of time when biased at voltages below the threshold voltage. Meanwhile, the lower the voltage is, the longer the switching time will be. The time scales from milliseconds to about 104s with decreasing voltage. Moreover, by applying a certain voltage between threshold voltage and Vmax, intermediate states are also obtained. The existence of filamentary microconducting channels in the organic layer is proposed to be responsible for the observed switching phenomenon.