Photoexcitable films with electronic capacitance and devices implementing same

Abstract

The invention generally concerns photoexcitable films and devices implementing same, which comprise chirally ordered cellulose nanocrystals (CNC) arrangements and QDs.

Description

[0001] PHOTOEXCITABLE FILMS WITH ELECTRONIC CAPACITANCE AND DEVICES IMPLEMENTING SAME

[0002] TECHNOLOGICAL FIELD

[0003] The invention generally contemplates photoexcitable films and devices formed therefrom.

[0004] BACKGROUND

[0005] The efficient separation of photogenerated electron-hole pairs into long-lived positive and negative charge carriers is a fundamental cornerstone in a variety of optoelectronic systems, particularly in photovoltaic applications such as artificial photosynthesis, photoelectrochemical water splitting, solar fuel production, and photodetection. Various device- specific mechanisms are employed to separate and transfer photogenerated charge carriers, competing against their recombination. For instance, systems based on doped silicon require p-n junctions, while organic photovoltaics lean on donor and acceptor energy level offsets, and quantum dot- sensitized solar cells use preferential injection kinetics into either electron or hole transport mediums. Each method has its hurdles. Inorganic semiconductors' doping concentration limits - beyond which they degenerate at room temperature - impede nanoscale charge separation and device miniaturization. Meanwhile, organic photovoltaics face low opencircuit voltages due to non-radiative decay, and quantum dot- sensitized solar cells experience unfavorable internal and interfacial charge recombination.

[0006] In addressing the challenge of efficient charge separation, the integration of chiral biopolymers and nanostructures provides opportunities not found in conventional semiconductor devices. Chiral molecules can act as spin filters, a phenomenon known as the Chiral-Induced Spin Selectivity (CISS) effect. While the precise mechanisms combine several effects, CISS main mechanism is attributed to spin-orbit coupling that aligns a charge carrier's spin with its linear momentum as it passes through chiral molecules. This break of symmetry, which is influenced by charge sign, current direction, and the handedness of the molecule, results in differential spin transfer probabilities, favoring the traversal of charges with a specific spin through the chiral molecule.

[0007] Building on this understanding, Peer et al., [1] employed quantum dots (QDs) and L- alpha helix polyalanine monolayers to develop a device that achieves efficient charge separation at sub-5 nm length scales without the need for doping. A related effect was measured in chiral diodes emitting circularly polarized light (CPL).

[0008] REFERENCES

[0009] [1] Peer N, Dujovne I, Yochelis S, Paltiel Y. Nanoscale charge separation using chiral molecules. ACS Photonics. 2015;2(10):1476-1481.

[0010] GENERAL DESCRIPTION

[0011] In view of the deficiencies associated with the existing developments in the field, the inventors have sought to meet the challenge by extending chirality-driven charge separation across larger scales, achieving higher voltages, a prerequisite for practical applications. The inventors have designed a unique device, incorporating a chiral hybrid film of cellulose nanocrystals (CNC) and quantum dots (QDs). The device achieves superior charge separation by leveraging the chirality and higher chiral order of CNC together with enhanced dielectric properties.

[0012] As known in the art, CNC is a versatile nano-biomaterial which may be obtained from wood, cotton, bacteria, algae or from other cellulose-rich sources, and exhibits desirable properties such as self-assembly, biocompatibility, scalability, wide range of mechanical and rheological properties. The crystalline rod-like CNC particles are composed of chiral D-glucose units linked by glycosidic bonds, which are effective at dispersing a wide range of nanoparticles and are unique for their inherent chirality, observable at both the individual and bundle levels. When in water, CNC particles form chiral nematic liquid crystals, with the CNC nanorods being locally oriented and rotated in a helical pattern around an axis. The left-handed helical arrangement can be particularly retained in solid-state CNC films formed through self-assembly. Notably, this chiral ordering of CNC can be influenced by magnetic fields, an effect that is amplified when the chiral CNC is decorated with magnetic particles, e.g., nanoparticles. Furthermore, controlling the spin using magnetic particles or substrates affects a higher helical chiral order during film formation. This magnetic control provides the ability to tune chirality and investigate its role in charge separation processes.

[0013] To explore this, three distinct film variants, each subjected to one of three different drying conditions, were prepared. One was placed on a magnet's north pole, disrupting the higher order helical chirality. The second was placed on the magnet's south pole, and the third was dried in absence of a magnetic field, under conditions which preserved the higher order helical chirality. Under circularly polarized light (CPL) excitation above the bandgap energy, the QDs in the device generated electron-hole pairs with specific spin states. The polarization of the incident light defines the spin direction, with right and left polarizations leading to spin-up and spin-down electrons, respectively. This enables formation of electron-hole pairs with equal sign of spin states

[0014] By selectively controlling the electron-hole spin states with distinct CPL, the transfer probability of charges through the chiral CNC film may be manipulated. Notably, right CPL (RCPL) and left CPL (LCPL) generate electrons and holes with either favored or disfavored spin states, based on the Chiral-Induced Spin Selectivity (CISS) effect. This transfer probability through the chiral CNC depends on both the charge sign and the favored spin state.

[0015] Furthermore, the CNC particles have the potential to imprint their chirality onto the QDs, an effect originating from strong spin-orbit coupling at the surfaces of the QDs where chiral molecules adsorb. This chiral imprinting on the QDs further amplifies the response to one circular polarization direction. Following CPL excitation, ejected electrons exhibiting the favored spin state readily traverse through the chiral CNC away from the QD. Conversely, traversal in the opposite direction, towards the QD, with the same favored spin state is less likely. Holes, sharing the same spin state sign as the electrons, lack the necessary spin state for effective migration in the same direction as the electrons within the CNC film, preferring instead to traverse oppositely. As long as charge carriers spin states remain unchanged, this hinders their recombination.

[0016] Moreover, following charge ejection from excited QDs and initial charge separation, charges may tunnel to trap states within the CNC matrix, even after spin relaxation. Alternative trapping models, supported by empirical data, propose that ejected charges interact with a dielectric and polarizable environment. Once in the CNC matrix, the ejected charge induces a reaction field, which can stabilize the charge, resulting in a self-trapped state. Notably, this stabilization energy of charges or dipoles is proportional to the matrix's dielectric properties, with CNC having a relatively high dielectric constant of ~6.

[0017] To probe the spin-dependent electron transfer mediated by the chiral CNC and the resulting charge separation, photoluminescence measurements were applied, specifically utilizing the quantum-confined Stark effect (QCSE). Typically, under an externally applied electric field, the QCSE manifests as a red-shift in the position of the emission peak, accompanied by a decrease in the fluorescence energy emitted. In this setting, a durable accumulation of separated, trapped charges, mediated by the chiral CNC's handedness, is predicted to establish a localized electric field around the QD with a specific dipole orientation. This localized field is expected to trigger the QCSE and to interact with any externally applied field. This interaction could either amplify or attenuate the QCSE, contingent upon the orientation of the external field, and the orientation of the local field.

[0018] Utilizing a sequence of varying CPL excitations and deliberate alterations to the inherent chirality of the device, distinct correlations with the resulting spectral shifts were observed under applied external voltage bias. Echoing the asymmetry inherent to the CISS effect, certain direction combinations of the CPL and voltage bias yielded substantial spectral shifts. In addition, each subsequent light excitation prompted a further spectral shift, indicating enhanced local charge separations within the device, even in the absence of an external voltage bias. These local separations contributed to a significant and enduring charge separation across length scales exceeding 1 pm, manifesting as a built-up directional dipole that enables to reach as much as 7nm average stark shift using simple symmetric spherical QDs. To reset the device for subsequent measurements, a discharge process was crucial to neutralize this accumulated dipole.

[0019] The unique and efficient charge separation and charge storge exhibited in photoexcitable films of the invention open the door for the development of photoexcitable devices having electronic capacitance, which may be used in a variety of electronic, optic and various optoelectronic systems and applications.

[0020] In a first aspect of the invention there is provided a photoexcitable chiral arrangement comprising a chiral assembly of CNC nanorods and quantum dots (QDs), excitable to generate mobile electron-hole pairs, the CNC arrangement being configured for trapping electrons and holes in trapping sites therewithin. Further provided is a photoexcitable chiral arrangement comprising a chiral assembly of CNC nanorods and quantum dots (QDs), the arrangement being configured so that mobile electron-hole pairs are generated due to incidence of light, and electrons and holes become trapped in trapping sites therewithin.

[0021] The invention further provides a photoexcitable ordered CNC arrangement comprising CNC nanorods helically oriented around a common axis, the arrangement comprising a distribution of quantum dots (QDs) selected for generating under light mobile electron-hole pairs, wherein the CNC arrangement is configured for trapping electrons and holes in trapping sites therewithin.

[0022] Further provided is a photoexcitable ordered CNC arrangement comprising CNC nanorods helically oriented around a common axis, the assembly comprising a distribution of quantum dots (QDs) and magnetic nanoparticles, wherein the QDs are selected for generating under light mobile electron-hole pairs, wherein the CNC arrangement is configured for trapping electrons and holes in trapping sites therewithin.

[0023] Excitation by light, e.g., polarized light, such as by a circularly polarized light beam, e.g., laser beam, induces charge separation in the active layer or photoexcitable film, at room temperature. The QDs in the arrangement are excited, following the optical selection rules and leading to formation of electron-hole pairs with specific spin states that correspond with the polarization of the light beam. The electron and hole undergo tunneling to the chiral environment through the chiral-induced spin selectivity (CISS) effect. This tunneling mostly occurs along the direction of the chiral axis of the system. Once the charges reach the chiral environment, they become trapped in trapping sites and do not recombine. Recombination does not occur for two primary reasons: First, the CISS effect inhibits recombination as it would require the electron and hole to flip their spin states- this process typically requires additional energy and is unlikely to occur spontaneously, thus maintaining charge separation, and second, the surrounding environment is dielectric rather than conducting. The lack of conducting pathways restricts the recombination of the charges, further promoting their separation. As a result of the aforementioned processes, the charges remain separated, creating an electric field gradient along the chiral axis over time.

[0024] For constructing a photoexcitable device having capacitor characteristics, the chiral arrangement of CNC nanorods may be formed as an easily applied photoactive or photoexcitable film, comprising a photoexcitable ordered CNC arrangement, as disclosed herein.

[0025] Further provided is a film comprising a photoexcitable ordered CNC arrangement, as disclosed herein, and device comprising same. The film may be a stand-alone film on which the arrangement is formed, and which may be used as such for fabricating electronic, optical or optoelectronic devise. In other alternatives, the arrangement may be directly formed as an active layer of a device. In some embodiments, the photoexcitable arrangement is formed as an active layer on a metallic surface, or a metal contact, e.g., a gold surface, in an electronic, optical or optoelectronic device. This arrangement is generally and without limitation depicted in Fig. 1, wherein a thin adhesion layer formed of titanium was evaporated on a Si / SiCh substrate material followed by a layer of gold. The active layer may be formed by depositing a dispersion of quantum dots (QDs), such as core / shell CdSe / ZnS in a CNC suspension that may comprise also magnetic nanoparticles. The deposition of the active layer was followed by deposition of a thin capping layer such as AI2O3. A layer of transparent and conducting layer of ITO was deposited on the capping layer, followed by evaporation of a gold strip.

[0026] According to some aspects, a film is provided which comprises an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods, wherein the arrangement comprises quantum dots (QDs) arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation upon excitation with a polarized light and charge storage within the arrangement.

[0027] A device is further provided which comprises a film excitable by polarized light, the film comprises an arrangement of CNC nanorods helically arranged around a common chiral axis being substantially perpendicular to the film surface, and comprising a distribution of magnetic nanoparticles and QD populations, wherein the excitation by a polarized light leads to formation of electron-hole pairs and formation of an electric field gradient along the chiral axis, wherein the electron-hole pair having a spin state corresponding with the polarized light.

[0028] A photocapacitor device is provided which comprises a single electronic device comprised of a photoexcitable active layer comprising an arrangement of CNC nanorods helically arranged around a common axis, and a plurality of QDs distributed within the arrangement; the photocapacitor device further comprising a metal layer at a first side of the active layer and a metal electrode at a second side of the active layer. A photocapacitor device is further provided for responding to light of a selected polarization, said device comprising an arrangement of a plurality of CNC nanorods helically arranged around a common axis, and a plurality of magnetic nanoparticles and QDs distributed within the arrangement; wherein the arrangement is formed on a substrate in the form of a layer or a film.

[0029] The invention further provides a device comprising an active layer or a photoexcitable film as disclosed herein, wherein the active layer or film is formed by deposition of a dispersion of QDs in a suspension comprising the CNC and optionally the magnetic nanoparticles, under conditions forming and preserving the ordered chiral structure of the film. The conditions used may involve any one of the following:

[0030] -deposition and slow drying under controlled conditions (such as 9-20°C, 2-7 days);

[0031] -application of a constant magnetic field during evaporation of the medium: due to the negative diamagnetic anisotropy of the CNC nanorods, the CNC nanorods align perpendicularly to the magnetic field, promoting uniformly oriented helices;

[0032] -deposition and drying when placed on the north pole, or the south pole of a magnet, at a constant magnetic field of e.g., 200 mT, generated by a magnet, e.g., a disklike magnet located below the deposited device.

[0033] The thickness of the active layer or film, independent of the method of its preparation or deposition, is typically in the micrometric scale. In some embodiments, the thickness of the photoexcitable layer or film is between 900nm and 2 microns. In some embodiments, the thickness is between 900 nm and 1000 nm (1 micron), between 900 nm and 1.1 microns, between 900 nm and 1.2 microns, between 900 nm and 1.3 microns, between 900 nm and 1.4 microns, between 900 nm and 1.5 microns, between 900 nm and 1.6 microns, between 900 nm and 1.7 microns, between 900 nm and 1.8 microns, between 900 nm and 1.9 microns, between 1 micron and 1.1 microns, between 1 micron and 1.2 microns, between 1 micron and 1.3 microns, between 1 micron and 1.5 microns, between 1 micron and 1.6 microns, between 1 micron and 1.7 microns, between 1 micron and 1.8 microns, or is between 1 micron and 1.9 microns.

[0034] In some embodiments, the thickness is about 1 micron ± 0.1 microns.

[0035] The term "quantum dots " (QDs), used interchangeably with “nanoparticles”, refers to nanocrystal forms of any semiconductor material known in the art. The QDs may be provided in a variety of compositions and forms, e.g., as nanoparticles, as core-shell systems, or as multi-core systems, as a single uniform or homogenous population of QDs or as a mixed population of QD, which may be formed of two or more QD populations of different composition, sizes and form. In some embodiments, the QDs are non-core- shell nanoparticles. In other embodiments, the QDs are core-shell nanoparticles.

[0036] The QDs may be of a semiconductor material selected, for example, from Groups II- VI, III-V, III- VI, IV- VI of the Periodic Table. Such materials may include

[0037] In some embodiments, the QDs are of a III / V material. Non-limiting examples of III / V materials include InAs, GaAs, GaP, GaSb, InP, InSb, AlAs, A1P, AlSb and alloys such as InGaAs, GaAsP, InAsP.

[0038] In some embodiments, the QDs are of a III / VI material. Non-limiting examples of III / VI materials include InS, ImSa. InSe, ImSes, I Ses, ImSes, InTe, ImSes, GaS, Ga2Se3, GaSe, Ga2Se3, GaTe, Ga2Te3, ImSes-xTex, GaTeSe, and (GaxIni-x)Se3, wherein x is zero or 1.

[0039] In some embodiments, the QDs are of a II / VI material. Non-limiting examples of such II- VI materials include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe and alloys such as CdZnSe, CdSSe, ZnSSe and the like.

[0040] Non-limiting examples of suitable QD materials include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, A1P, AlSb, InGaP, ZnSeTe, ZnCdS, ZnCdSe, and CdSeS and core-shell forms thereof.

[0041] In some embodiments, the QDs are core-shell particles of a material selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, A1P, and AlSb. In some embodiments, the QD is a core shell formed of CdSe or ZnS.

[0042] In some embodiments, the QD is a CdSe / ZnS core-shell structure.

[0043] In some embodiments, the QDs may be selected amongst blue or red QDs. In some embodiments, where mixed populations of QDs are desired or in case of multilayered arrangements comprising stacked arrangements of the invention, each arrangement in the stack may comprise a different population of QDs. In some cases, one arrangement may utilize red QDs and another may utilize blue QDs. The red and blue QDs have the same meaning as known in the art and are QDs selected to emit red or blue light, respectively, upon excitation.

[0044] The magnetic nanoparticles, when present, may be selected amongst magnetically responsive particles or generally particles which are able to be attracted by a magnetic field. When selecting suitable magnetic nanoparticles, the nanoparticles should be such not to aggregate in the absence of a magnetic field. The magnetic nanoparticle may have any symmetric shape, such as a sphere or a cube, or any asymmetric shape.

[0045] The magnetic nanoparticles can suitably be ferrimagnetic, or ferromagnetic and may be selected amongst such materials available and known in the art. In some cases, the magnetic nanoparticles may comprise magnetite (FesCU) or maghemite (gamma- Fe2O3). Magnetic alloys comprising iron, nickel and / or cobalt may also be used.

[0046] Thus, in a device of the invention, the film comprises an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods, wherein the arrangement comprises core-shell CdSe / ZnS QDs, and optionally magnetite nanoparticles, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide a measurable capacitance (or to provide charge separation and storage).

[0047] As disclosed herein, devices of the invention comprising an active layer or film as disclosed herein, may be formed by deposition of a medium comprising the CNC, QDs, and optionally the magnetic nanoparticles, under condition forming and preserving the ordered chiral structure of the film. The medium is typically a liquid dispersion / suspension which comprises the three components. In a method of device fabrication, a suspension comprising the CNC and optionally the magnetic nanoparticles are formed, whereby the magnetic nanoparticles, when present, are grafted (e.g., by selfordering) onto or assemble on the CNC nanorods such that magnetic ordering (if desired) of the nanorods may be possible. Addition of QDs into the CNC suspension or to the CNC-magnetic particles (e.g., CNC-FesC ) suspension provides a QD dispersion that may be deposited onto a substrate, as disclosed herein.

[0048] Deposition may be achieved by any method known in the art to obtain a film. The deposition may be achieved by printing, spray coating, smearing, spreading, dipping, spin coating, slot coating, or by any other method known in the art. Thus, device fabrication need not involve expensive and complex deposition methods. Devices of the invention may be regarded as smearable devices, whereby the active layer, i.e., the photoexcitable film, is formed by smearing the medium comprising the CNC, QDs, and magnetic nanoparticles on a metallic surface or generally on a substrate.

[0049] Spreading a medium comprising the CNC, QDs, and optionally the magnetic nanoparticles, under condition forming and preserving the ordered chiral structure of the film may be achieved by facile spreading on any substrate. One unique embodiment of the invention concerns spreading of the medium on a flexible substrate or on a surface such objects as cars, buildings, table, roof panels and others.

[0050] The efficient charge separation and charge storge demonstrated for devices of the invention is vital in various optoelectronic systems. Devices of the invention harness the unique combination of chirality and enhanced dielectric properties of cellulose nanocrystals (CNC), and thus pave the way for numerous potential applications, ranging from self-assembled devices that combine photovoltaic cells with electric capacitance (and still being green energy), to optical electric-field hybrid sensors and biosensors.

[0051] Thus, the invention further provides a device according to the invention, wherein the device is an optical device, and electronic device, or an optoelectronic device.

[0052] In some implementations, the device is a photovoltaic cell with a built-in capacitor for storing energy.

[0053] In some implementations, the device is a flexible self-assembled battery.

[0054] In some implementations, the device is a tunable and flexible stress and optical sensor.

[0055] In another aspect, there is provided a photovoltaic cell (PV cell), the PV cell comprising a photoexcitable film or surface comprising or provided with an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods, wherein the arrangement comprises QDs such as core-shell CdSe / ZnS QDs, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation and charge storage upon excitation with a polarized light.

[0056] Also provided is a photovoltaic cell (PV cell), the PV cell comprising a photoexcitable film comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods, wherein the arrangement comprises a plurality of QD layers structured to provide an increase in bandgap between an inner QD layer to an outermost QD layer. The layered structure could use different types of QDs with different layers covering better the full solar spectrum (similar to Multi-j unction (MJ) solar cells). This multilayer structure could be ordered to improve cell efficiency.

[0057] The invention further provides an energy storage unit, e.g., a battery, comprising a photoexcitable film having electronic capacitance, wherein the film comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods, wherein the arrangement comprises QDs such as core-shell CdSe / ZnS QDs, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation and charge storage upon excitation with a polarized light.

[0058] Further provided is a sensor, such as an optical sensor or a stress sensor comprising a photoexcitable film according to the invention.

[0059] In some embodiments, the sensor is a stress sensor. A device of the invention may be configured for determining a difference in electric potential due to mechanical stress imposed onto a sensor comprising a photoexcitable film according to the invention, wherein a change in a potential measured upon excitation of said film indicates a deformation of the film due to mechanical stress. This can be used for example to sense stress and cracks and bridges and structures as well as to act as a trespassing sensor on the ground.

[0060] The invention further concerns kits for fabricating films and devices according to the invention, the kits comprise a medium comprising CNC and QDs, each as described herein, and optionally magnetic particles as disclosed.

[0061] The invention further provides:

[0062] A photoexcitable chiral arrangement comprising a chiral assembly of CNC nanorods and quantum dots (QDs), excitable by light to form mobile electron-hole pairs, the arrangement being configured for separating and trapping of electrons and holes in trapping sites within the chiral arrangement.

[0063] Also provided is a photoexcitable ordered CNC arrangement comprising CNC nanorods helically oriented around a common axis, the arrangement comprising a distribution of quantum dots (QDs) selected for generating under light mobile electronhole pairs, wherein the arrangement is configured for trapping electrons and holes in trapping sites therewithin.

[0064] A film of a photoexcitable arrangement according to the invention is further provided. In some cases, the film implementing an arrangement according to the invention having a thickness between 900nm and 2 microns.

[0065] In some cases, the quantum dots are provided as nanoparticles, as core-shell systems, or as multi-core systems.

[0066] In some cases, the quantum dots are of a material selected from a Group II- VI, III-V, III- VI, IV- VI semiconductor material.

[0067] In some cases, the QDs are of a III / V material. In some cases, the III / V material is selected from InAs, GaAs, GaP, GaSb, InP, InSb, AlAs, A1P, AlSb, InGaAs, GaAsP, and InAsP.

[0068] In some cases, the QDs are of a III / VI material.

[0069] In some cases, the III / VI material is selected from InS, ImSa, InSe, ImSes, I Ses, ImSesJnTe, ImSes, GaS, Ga2Se3, GaSe, Ga2Se3, GaTe, Ga2Te3, ImSci-xTcx. GaTeSe, and (GaxIni-x)Se3, wherein x is zero or 1.

[0070] In some cases, the QDs are of a II / VI material.

[0071] In some cases, the II / VI material is selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdZnSe, CdSSe, and ZnSSe.

[0072] In some cases, the QDs are of a material selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, A1P, AlSb, InGaP, ZnSeTe, ZnCdS, ZnCdSe, and CdSeS and core-shell forms thereof.

[0073] In some cases, the QDs are core-shell particles of a material selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, A1P, and AlSb.

[0074] In some cases, the QDs are core-shell structures formed of CdSe or ZnS.

[0075] In some cases, the QDs are CdSe / ZnS core-shell structures.

[0076] In some cases, the arrangement comprises magnetic nanoparticles.

[0077] In some cases, the magnetic nanoparticles are ferrimagnetic, or ferromagnetic.

[0078] In some cases, the magnetic nanoparticles are magnetite (FC3O4) or maghemite (gamma-Fe2O3).

[0079] In some cases, the magnetic nanoparticles are formed of a magnetic alloy comprising iron, nickel and / or cobalt.

[0080] A film is provided which comprises a photoexcitable ordered CNC arrangement comprising chirally ordered cellulose nanocrystals (CNC) nanorods helically oriented around a common axis, wherein the arrangement comprises core-shell CdSe / ZnS QDs, and optionally magnetite nanoparticles, wherein the QDs are arranged within the arrangement to provide a measurable capacitance.

[0081] In some cases, the film is implemented as an optical device or in an optical device, an electronic device, or an optoelectronic device.

[0082] In some cases, the device is a photovoltaic cell with a built-in capacitor for storing energy.

[0083] In some cases, the device is a flexible self-assembled battery. In some cases, the device is a tunable and flexible stress and optical sensor.

[0084] In some cases, the device or film is formed on flexible substrate.

[0085] In some cases, the device or film is formed by spreading.

[0086] In some cases, the device or film is formed on an external surface of a 3D object, such as objects exposed to radiation.

[0087] The invention further provides devices implementing a film or an arranged according to the invention. The devices may be photocapacitor devices, energy storage devices or photovoltaic devices.

[0088] Generally speaking, the device contemplated comprises a photoexcitable chiral arrangement comprising a chiral assembly of CNC nanorods and quantum dots (QDs), the arrangement being configured so that mobile electron-hole pairs are generated due to incidence of polarized light, and electrons and holes become trapped in trapping sites therewithin.

[0089] In some cases, the device comprises a photoexcitable film or a photoexcitable surface comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods helically oriented around a common axis, wherein the arrangement comprises QDs arranged within the arrangement of chirally ordered CNC to provide charge separation upon excitation with a polarized light and charge storage within the arrangement.

[0090] In some cases, the arrangement comprising a distribution of magnetic nanoparticles and QDs, wherein the excitation by a polarized light leads to formation of electron-hole pairs and formation of an electric field gradient along the chiral axis, wherein the electron-hole pair having a spin state corresponding with the polarized light.

[0091] In some cases, the device is arranged as a tandem device.

[0092] A photocapacitor comprising a single electronic device comprised of a photoexcitable active layer comprising an arrangement of a plurality of CNC nanorods helically arranged around a common axis, and a plurality of QDs distributed within the arrangement; a metal layer at a first side of the active layer and a metal electrode at a second side of the active layer.

[0093] A photocapacitor device for responding to a light of a selected polarization, said device comprising an arrangement of a plurality of CNC nanorods helically arranged around a common axis, and a plurality of magnetic nanoparticles and QDs distributed within the arrangement; wherein the arrangement is formed on a substrate in the form of a layer or a film.

[0094] A photovoltaic cell (PV cell), the PV cell comprising a photoexcitable film comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods helically arranged around a common axis, wherein the arrangement comprises QDs such as core-shell CdSe / ZnS QDs, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation and charge storage upon excitation with a polarized light.

[0095] An energy storage unit comprising a photoexcitable film having electronic capacitance, wherein the film comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods helically arranged around a common axis, wherein the arrangement comprises QDs such as core-shell CdSe / ZnS QDs, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation and charge storage upon excitation with a polarized light.

[0096] A device is further provided which comprises a plurality of stacked films of a photoexcitable arrangement according to the invention. In some cases, each arrangement comprises a different QD population. In some cases, the device comprised two or more stacked arrangements connected in series, such that a top arrangement is configured to absorb high energy photons and a bottom arrangement is configured to absorb low energy photons.

[0097] In some embodiments, in the stacked arrangements the top arrangement comprises blue QD and the bottom arrangement comprises red QD.

[0098] Any device according to the invention may be a stacked device comprising two or more photoexcitable films, wherein optionally each of the two or more photoexcitable films comprises a different population of QDs. Also, the devices may be arranged as a tandem device.

[0099] BRIEF DESCRIPTION OF THE DRAWINGS

[0100] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figs. 1A-E provide a schematic illustration of the device structure, measurement setup, and charge separation mechanism. (A) Illustration of the device structure. On a Si / SiO2 substrate, a thin Ti adhesion layer was evaporated followed by an Au layer, next a multilayer structure of dispersed core / shell CdSe / Zns QDs within a CNC-Fe3O4 suspension was deposited, followed by a thin AI2O3 capping layer, on top of that, a layer of transparent yet conducting layer of ITO was deposited, and finally a small Au strip was evaporated on top, to aid with the bonding procedure. (B) Measurement setup. The sample is connected to a voltage source and positioned on an XYZ stage to enable precise alignment with a focused laser beam. The beam is controlled by a shutter to regulate the exposure time of the sample. It then traverses a quarter waveplate to generate circular polarization before being focused onto the sample through a convex lens. The emitted fluorescence is collected by a microscope objective, passes through a high pass filter, and is then focused using another convex lens. The focused fluorescence is coupled to an optical fiber, which is further connected to a spectrometer that is in turn connected to a computer for analysis. Charge separation mechanism. (C) A single QD is excited by a circularly polarized laser beam. This excitation follows the optical selection rules and leads to the formation of an electron-hole pair with a specific spin state. (D) The charges, i.e., the electron and hole, undergo tunneling to the chiral environment through the CISS effect. This tunneling mostly occurs along the direction of the chiral axis of the system. (E) Once the charges reach the chiral environment, they become trapped in the trapping sites of the system. The charges do not recombine for two primary reasons: Firstly, the CISS effect inhibits recombination as it would require the electron and hole to flip their spin states. This process typically requires additional energy and is unlikely to occur spontaneously, thus maintaining charge separation. Secondly, the surrounding environment in this case is dielectric rather than conducting. The lack of conducting pathways restricts the recombination of the charges, further promoting their separation. As a result of the aforementioned processes, the charges remain separated, creating an electric field gradient along the chiral axis over time.

[0101] Figs. 2A-F provide SEM of surface and indentation of QDs-CNC-FesCU film. SEM of surface: A) dried without magnet. B) dried under south facing magnetic field. C) dried under north facing magnetic field. SEM of indentation: D) dried without magnet. E) dried under south facing magnetic field. F) dried under north facing magnetic field. Fig. 3 shows a spectral response to an applied electric field. Spectral shift response under varying E-field magnitudes in a device dried without magnet and excited with LCPL. The figure compiles 20 sessions of QD emission measurements per each bias level (0V, 5 V, 10V, 15V); within each session, five consecutive spectra (1 sec integration time each) were averaged, followed by device discharge. Lorentzian functions were fitted to the spectra to identify the peak wavelength (Amax). Averaged emission spectra across sessions for each bias level. Inset: Corresponding average emission peak shifts per bias level. Error bars represent the standard deviations of the emission peak shifts.

[0102] Fig. 4 shows the mean emission peak shift in response to an applied electric field for different light polarizations and chiral orders. Mean emission peak shifts are depicted in response to voltage bias of 5V applied to each one of the device variants: dried on north, south, or absent a magnet (none), and excited with left (L) or right (R) CP. The figure compiles 20 sessions of QD emission measurements per device variant and light polarization; within each session, five consecutive spectra (1 sec integration time each) were averaged, followed by device discharge. Lorentzian functions were fitted to the spectra to identify the peak wavelength (Amax). Error bars represent the standard deviations of the emission peak shifts.

[0103] Fig. 5 shows the maximal spectral response to an applied electric field, reversed bias. Spectral shift response under 0V and -15V (0 to 120 KV / cm) negative bias (with respect to Fig. 2) in a device dried without magnet and excited with left CP. The figure compiles 20 sessions of QD emission measurements per each bias level (0V, -15V); within each session, five consecutive spectra (1 sec integration time each) were averaged, followed by device discharge. Lorentzian functions were fitted to the spectra to identify the peak wavelength (Amax). The figure shows the averaged emission spectra across sessions for each bias level.

[0104] Fig. 6 shows the dynamics of the Emission Peak Wavelength. The figure is tracking the evolution of the maximum emission peak wavelength (Amax) under different bias levels (0V, 5V, 10V, 15V) for device variant dried without magnet and excited with left CPL. The data presented comprises 220 measurement sessions across each bias level. Every session is part of a cycle, which consists of a 'laser on' period of 10 seconds, immediately followed by an 11-second 'laser off rest interval. During each 'laser on' period, two separate 5-second spectra recording sessions occur. Each of these recording sessions involves capturing five consecutive spectra (with an integration time of 1 sec each), which are then averaged to produce a single session spectrum. A total of 110 such 'laser on' cycles were executed. The device was not discharged at any point during the experiment. Inset: Two-Round Emission Peak Wavelength Dynamics Separated by a Discharge, No Bias Applied. The inset shows two consecutive sets of measurements of the evolution of the maximum emission peak wavelength (Amax) for a device variant dried without a magnet and excited with left CPL, and with no applied bias (0V). Following the initial set of 220 sessions, the device underwent a single discharge (represented by a doted green line), achieved by short-circuiting for 20 seconds, before the second set of 220 sessions commenced.

[0105] Fig. 7 is the voltage output measured by striking pure CNC thin film by constant force applied by Instron compression testing.

[0106] Figs. 8A-B provide TEM scans of A) CNC without connected MNP. B) 15 Minute CNC-MNP composite. Yellow arrow pointing to aggregates and red circles pointing to iron oxide MNP on CNC particles. Scale bar is lOOnm.

[0107] Fig. 9 shows the voltage output of pure CNC films and CNC-MNP with 10-minute growth time composite films.

[0108] Fig. 10 shows the average voltage output of CNC-MNP mixed with pure CNC ratios at of 1:2, 1:5 and 1:10 of CNC-MNP:CNC.

[0109] Fig. 11 shows the spectral response to an applied electric field. Spectral shift response under varying E-field magnitudes in a device variant based on a “non-chiral” QDs / CNC hybrid film that was rapidly dried in an oven at 80 degrees Celsius for two hours (and without a magnet). The figure compiles 20 sessions of QD emission measurements per each bias level (0V, 5V, 10V, 15V); within each session, five consecutive spectra (1 sec integration time each) were averaged, followed by device discharge. Lorentzian functions were fitted to the spectra to identify the peak wavelength (Amax). Averaged emission spectra across sessions for each bias level. Inset: Corresponding average emission peak shifts per bias level. Error bars represent the standard deviations of the emission peak shifts.

[0110] Fig. 12 depicts the dynamics of the emission peak wavelength. The figure is tracking the evolution of the maximum emission peak wavelength (Amax) under different bias levels (0V, 5 V, 10V, 15 V) for the device variant based on a “non-chiral” QDs / CNC hybrid film that was rapidly dried in an oven at 80 degrees Celsius for two hours (without a magnet). Each recording cycle involves capturing five consecutive spectra (with an integration time of 1 sec each), which are then averaged to produce a single session spectrum. A total of 100 such recording cycles were executed. The device was not discharged at any point during the experiment.

[0111] DETAILED DESCRIPTION OF EMBODIMENTS

[0112] Results

[0113] Device fabrication and measurement setup

[0114] The design and construction of the chiral device and experimental setup are illustrated in Fig. 1. The experimental setup is designed to facilitate charge separation in photoexcited QDs and measure their emission spectrum both with and without an applied electric field. At the core of this device is a multilayer structure shown in Fig. 1A. Here, we dispersed spherical core / shell CdSe / ZnS QDs (~3.8 nm diameter core, ~9 nm diameter with shell) within a CNC-Fe3O4 suspension, deposited the mixture onto a SiO2 / Ti / Au substrate, and then slowly dried it under controlled conditions (12°C, 4 days). The slow evaporation process is integral to preserving a more ordered chiral nematic structure in the dried film. Furthermore, evaporation at lower temperatures has been observed to reduce concentration and thickness gradients in the dried films.

[0115] Despite this, standard solvent evaporation is insufficient in controlling the overall CNC film architecture and can lead to variations among the local helices. In response to this issue, we drew on a method from earlier studies that involves applying a constant magnetic field during the slow evaporation process. Due to the negative diamagnetic anisotropy of the CNC rods, they align perpendicularly to the magnetic field, promoting uniformly oriented helices. Moreover, controlling the spin using magnetic particles or substrates can influence the higher helical chiral order. To utilize these effects, we incorporated FcTC superparamagnetic nanoparticles into the CNCs. Prior research has shown this step to amplify the CNCs magnetic susceptibility. Consequently, the alignment of CNCs under the magnetic field , and the required field strength to influence the CNCs chiral helical structure is substantially reduced.

[0116] To assess the influence of chirality, three unique device variants were prepared, with each attempting to modulate the chiral ordering of the CNCs. Following the deposition of the QDs-CNC-FcTC hybrid suspension onto the substrate, it was dried according to one of three conditions: positioned on the north pole of a magnet, on the south pole of a magnet, or absent a magnet. The magnet condition referred to a constant magnetic field of 200 mT generated by a disk-like magnet located beneath a Petri dish. Following the drying process, with or without the influence of the magnet, each resultant QDs-CNC-FesCU film exhibited a thickness of approximately 1 pm.

[0117] The fabrication process continued post-drying (Fig. 1A). A 30 nm AI2O3 isolation layer was deposited over the dried QDs-CNC-FcaCU film. Following this, a 100 nm transparent layer of indium tin oxide (ITO) was sputter-coated atop the isolation layer. The final step involved the deposition of a narrow Cr / Au electrode on the ITO layer. The active area of the finished device measured 3 mm by 3 mm.

[0118] Complementing the fabricated device, a custom measurement setup was designed, as depicted in Fig. IB. This configuration enables the photoexcitation of the QDs using either left- or right-handed CPL. The emitted fluorescence from the QDs is subsequently captured and analyzed by a spectrometer. To measure the QCSE, a synchronized modulated voltage source, connected via the Au electrodes, is capable of applying a bias to our device, thereby generating an electric field perpendicular to the QDs-CNC-Fe3O4 film surface.

[0119] Hybrid film Characterization

[0120] Circular dichroism (CD) spectroscopy was conducted on the dried films, reaffirming the preservation of the CNC film's chiral structure. The CD spectra exhibited a predominant transmission of LCPL for CNC samples dried either under a south magnetic field or without a magnet, as opposed to those dried under a north magnetic field. These results corroborate our previous studies on magnet-dried CNC.

[0121] Scanning Electron Microscope (SEM) images of the QDs-CNC-FciCU films are provided in Fig. 2, corresponding to each drying condition (without magnet, on north pole, or on south pole). The images present both top (Figs. 2A-C) and indentation views (Figs. 2D-F). As corroborated by the findings of Al-Bustami et al., the CNC film dried on the south magnetic pole (Figs. 2B and 2E) demonstrates a uniform pattern typical of left-handed chiral helicoidal arrangements. In this configuration, the helicoidal axis is nearly perpendicular to the film surfaces, akin to a Bouligand structure. In contrast, drying on the north pole of the magnet (Figs. 2C and 2F) disrupts this chiral order, leading to a more untwisted formation of the naturally left-handed helical CNC. The film dried without a magnet (Figs. 2A and 2D) exhibits a chiral organization similar to the sample dried on the south pole of a magnet.

[0122] Light Polarization and E-Field Impact on Spectral Shift

[0123] For each device variant (dried on north, south, or absent a magnet), optical spectra measurements were conducted separately under illumination with RCPL and LCPL (Fig. IB). The direction of the incident light is 45°. These measurements began without an applied E-field and were followed by additional measurements with varying E-field magnitudes to investigate their effect on the emission spectrum. After each measurement, the device was discharged before initiating the next one. This step was necessary to neutralize an enduring charge separation within the device, which conferred a capacitorlike behavior. Notably, this separation was triggered by light excitation, even in the absence of an external voltage bias. Without the discharge step, a carryover effect was noticed, whereby the starting emission of the following measurement session would already display the red-shifted emission noted at the end of the previous session. This observation further implies that the material has the capacity to sustain voltage and maintain charge separation through alternative pathways, even after the cessation of illumination or the removal of an external electric field.

[0124] The spectral shift responses to different external E-field magnitudes for a specific device variant are illustrated in Fig. 3. This variant was dried without a magnet, which allowed the film to preserve its chiral structure, and was then excited with LCPL. For each bias level (OV, 5V, 10V, 15V), 20 emission measurement sessions were done, discharging the device after each session. A Lorentzian fitting function was applied to the data from each session identifying the peak wavelength (Amax). The average of these 20 sessions represents the average spectrum for each bias level. Fig. 3 shows a progressive red shift in the average emission spectra of the QDs as the external E-field strength increases, while the inset of Fig. 3 focuses on the corresponding shift of the emission peak (Amax). This observed trend aligns with those documented in prior studies. However, as shown below the effect is remarkably larger considering the magnitude of the e-fields applied to the QDs-CNC-FcaCL film.

[0125] In order to estimate the E-field strength experienced by the QDs-CNC-FcaCL layer due to the externally applied bias, we used the ideal plate capacitor approximation, conceptualizing the ITO, AI2O3, and QDs-CNC-Fe3O4 layers as functioning like three capacitors in series, each with their own dielectric constants and width (additional details can be found in the supporting information). For example, an applied external bias of 15V to the whole device resulted in an estimated electric field of approximately 120 KV / cm on the QDs-CNC-FesCU layer, leading to a red shift of 2.83 nm (9 meV) in the emission peak.

[0126] Under comparable E-field magnitudes, such sizable emission peak shifts are unusual in the context of an ensemble of symmetric spherical QDs used in this study. In comparison with prior research, red shifts under 1 nm are common for similar ensembles of QDs at E-field strengths equivalent to ours. With an electric field magnitude tripled to 390 KV / cm, a 2.3 nm red shift was reported. At an even higher field magnitude of 600 KV / cm, about five to six times hours, a ~6.2 nm shift was documented.

[0127] Typically, transient local electric fields, arising from charge carriers on or near QD surfaces, present random orientations within a QD ensemble, and thus tend to nullify the average dipole component relative to an externally applied field. However, the notable average emission peak shifts we observe hint at a divergence from this common scenario. One conceivable explanation involves the formation of persistent local charge separation and thus electric fields around the QDs, exhibiting a non-negligible component that aligns with the direction of the externally applied field. As previously described, this externally applied field is oriented perpendicular to the QDs-CNC-Fe3O4 film (Fig. 1A) and would thus be parallel to the chiral CNC helices axes in devices that preserved this chiral organization.

[0128] To test the above conjecture, CPL was used to excite the QDs in devices with varying degrees of chiral order within the QDs-CNC-FcTU film. The polarization choice - left or right - selectively influences the electron-hole spin states. This, in turn, affects the probability of charge transfer through the CNC's helical chiral structure, enhancing or reducing the charge separation effect as a result of the CISS effect. A specific circular polarization should lead to a more pronounced and persistent local charge separation around the QDs compared to its counterpart depending on the localization of the spin wave function in the chiral potential. Therefore, in a chiral CNC structure and at a given bias voltage, varying spectral shifts are anticipated when comparing responses to different circular light polarizations.

[0129] Examining this proposition, the mean shift in emission peak (Amax) under a 5V external bias is illustrated in Fig. 4. This is measured across three distinct device variants — dried on north, south, or without a magnet — and excited with either LCPL or RCPL. As before, 20 emission measurement sessions were conducted for each device variant and light polarization, discharged the device after each session, and estimated the peak wavelength (Amax) from the Lorentzian fit. Note that the top and bottom contact are different generating an intrinsic difference in work function between the two metals.

[0130] Our findings reveal a notable difference in the emission peak shift between devices where the chiral helical ordering was preserved, i.e., those dried on a south pole of a magnet or without a magnet, and the device dried on the north pole of a magnet, where this ordering was compromised. When excited with left CPL, the peak shift for the former group in response to a 5V external bias was notably larger — exhibiting an order of magnitude difference compared to the right CPL. For instance, a 2.25 nm shift was observed for left CPL excitation versus a 0.14 nm shift for right CPL, in the device dried on a south pole of a magnet. However, for the device dried on the north pole of a magnet, no such significant difference was discernible between the magnitudes of the peak shifts in response to left CPL and right CPL excitation. This is expected as the secondary structure order is reversed in part due to the spin direction flip of the substrate.

[0131] To further study the spin induced self-organization of the developed hybrid material, another device variant was studied. A QDs-CNC hybrid film was rapidly dried in an oven at 80 degrees Celsius for two hours (and without a magnet). This expedited process compromises the preservation of the chiral helical order in the dried film. Upon exposure to a similar E-field strength of 120 KV / cm, the observed shift in the emission peak was ~0.5 nm, and no significant difference was observed between the magnitudes of the peak shifts when using LCPL compared to RCPL excitation. This shift is of a similar scale as that observed in the device dried on the north pole of a magnet (Fig. 4), where disruption of the helical chiral ordering had occurred.

[0132] Given our observation of large spectral shifts, particularly with LCPL excitation, we conjectured that there is a formation of local electric fields around the QDs with a directional component aligning along the axis of the external applied field. If the orientation of these local electric fields, either parallel or antiparallel to the external field, is random, we would not anticipate any significant difference in the spectral shift upon reversing the direction of the external bias voltage. Conversely, if the CISS effect influences the local electric fields, causing a preferred orientation, we would expect to see distinct spectral shifts when applying negative and positive biases of the same magnitude to the device.

[0133] Investigating this possibility, the spectra under OV and 15V negative bias for a device variant dried without a magnet is displayed in Fig. 5, thereby preserving the chiral organization, and subsequently excited with left CPL. The measurements mirrored the approach in Fig. 3, with the primary difference being the reversed direction of the applied bias. Upon applying a negative bias, a remarkably large spectral shift was observed, with the peak experiencing a red shift of 7.16 nm. Notably, this shift was 2.5 times larger than the 2.83 nm shift seen under identical conditions but with a positive bias, as previously shown in Fig. 3. This observation seems to diverge from previous studies, which have reported symmetry in the Stark shift's magnitude under reversed electric fields within QD ensemble measurements. Moreover, in our study, this 7.16 nm shift represents the largest we recorded across all device variations, light polarization conditions, and applied voltage biases within the 0V-15V range (up to 120 KV / cm).

[0134] Emission Dynamics

[0135] The full set of results seem to support the proposition that persistent local charge separation, and consequent electric fields around the QDs, are formed with their orientation influenced by the CISS effect. If these local fields indeed originate from a continuous build-up of photoexcited charge separation and demonstrate persistence, it would imply further spectral shifts with each subsequent light excitation, provided the device discharging process is prevented. Notably, these shifts should be observable even in the absence of an external voltage bias.

[0136] The evolution of the maximum emission peak wavelength (Amax) at each applied bias level (0V, 5V, 10V, 15V), for a device variant dried absent magnetic field, thereby preserving the chiral organization, and which was subjected to excitation via LCPL, is illustrated in Fig. 6. We conducted 220 emission measurement sessions for each bias level. In each recording period, the excitation laser was active for 10 seconds, recording two sessions, followed by a 11 -second interval with the laser off to allow the device to rest and cool. Notably, unlike previous experiments, the device was not discharged after each session. The time series in Fig. 6 selectively presents only the recording periods, excluding the non-recording intervals when the laser was off. A noticeable upward trend for the OV, 5V, and 10V lines, indicating a red shift in the emission peak wavelength with each subsequent light excitation. This effect is particularly evident in the OV time series. However, the 15V graph demonstrates only a mild upward trend, suggesting a saturation point. Furthermore, the initial vertical gap between the peak wavelength of each positive bias level and the OV level corresponds to the Stark shift measured for each bias level. Notably, the magnitude of this gap mirrors the Stark shift computed and showcased in Fig. 3 for the same device variant and excitation light polarization. Upon examining the OV graph more closely, we observe that the peak wavelength, after 220 light excitations (corresponding to 1100 seconds), reaches a red shift of ~1.5nm which is roughly similar to that induced by a 5V bias, as is evident from the initial peak wavelength of the 5V graph.

[0137] Fig. 6 inset illustrates the course of an experiment mirroring the procedures from Fig. 6, conducted only under zero bias (OV), with the device variant prepared without a magnet and excited with left CPL. The experiment comprised two consecutive sets of 220 sessions each, and after the first set, the device was discharged once by a 20-second short circuit before the second set commenced. An upward trajectory in the emission peak wavelength for each set of measurements, echoing the red shift pattern observed in Fig. 6 with each successive light excitation. Importantly, following the discharge of the device (noted at the second 1000 marker), there is a discernible reduction in the emission peak wavelength at the beginning of the second set, indicating a reversion to a value similar to the initial state of the first set. Notably, this pattern persisted even when a 24-hour break was introduced following the first set of measurements, after which the device was discharged, and the second set of measurements was conducted. These findings suggest that the cumulative light excitations not only yielded further localized charge separations within the QDs-CNC-FcTU film, but also that this process appears to contribute to a substantial and enduring charge separation across the device's length scales, exceeding 1 pm, and results in a built-up dipole across the device.

[0138] CPL and induced polarization

[0139] To account for the above observations, the following model is proposed. When shining CPL to a noncentro symemtric solid like CdSe, electron and hole pairs are excited and lead to a de photocurrent (Jph). We note that quantum states at opposite momentum (± k) carry opposite angular momentum (including both orbital and spin) and opposite velocity when inversion symmetry is broken and the CPL photon also carries angular momentum (h). Because of the angular momentum selection rule, RCPL excites states mainly in one momentum valley while LCPL excite states mainly in the opposite valley, leading to excited carriers with opposite velocities. Therefore, RCPL and LCPL generate opposite photocurrent, called injection current or circular photogalvanic effect (CPGE) in literature. For the chiral material with random orientation, which is the case of CdSe nanoparticles in a chiral matrix, the photocurrent direction is along the light propagation axis and current along other directions are averaged to zero. In an open-circuit device, the photocurrent leads to a finite polarization, i.e., an open circuit voltage, Voc= Jph■ R , where R is internal resistance. Because R is large in the device, it is not surprising to realize a large voltage. In contrast, Vocof a p-n junction solar cell is limited by the band gap of material. In the injection current scenario, Vocis free from such a constrain and generates a giant electric in the capacitor setup. For the given CPL excitation, the material chirality is the key to determine the photocurrent direction and thus the induced E-field direction.

[0140] In the present experiment, we observe a de current (probed by the E-field in QCSE) generated by irritating CPL where the CPL handedness controls the de current direction. This is an inverse process of the anomalous CPL emission reported in chiral polymers, in which the de current direction controls the CPL handedness. Therefore, it is natural that both phenomena originate in the unique angular momentum in the chirality - light interaction.

[0141] CNC and CNC-FmO magnetic nanoparticles (MNP) composite film piezoelectric voltage output

[0142] Testing voltage output under controlled load

[0143] Pure CNC film (2 cm X 2cm, 40 ± 5 m thickness) were placed in an insulating mould with two copper electrodes, one on each side of the film. The mould was placed in an Instron (Instron 3345) machine and set to be pressed at 5 N in a cyclical compression program. The voltage was measured and recorded on a digital multimeter and presented.

[0144] Fig. 7 shows the voltage output in real time with the force applied by the Instron. The force applied is 5.8±0.4N and the recorded voltages received is 28.8± 1.2mV. The voltage received was roughly constant and does not vary greatly across strikes. Magnetic nanoparticle growth on CNC

[0145] A suspension of composite CNC-MNP particles was synthesized.

[0146] 40gr of a 2 wt% suspension of CNC particles was diluted with 160gr of DW to achieve a 0.4wt% suspension. The diluted suspension is heated to 70 °C. Then, 0.17 g of ferric chloride hexahydrate and 0.11 g of ferrous sulfate heptahydrate were added under magnetic stirring. 400 pl of ammonium hydroxide was diluted to 20 mL with DW water and preheated to 70 °C. The base solution was dropwise added to the CNC suspension and left to react in increasing time intervals of 5 minutes, 10 minutes, or 15 minutes, to allow growth of different sized particles. The resulting solutions were quickly cooled to room temperature using an ice bath to stop the reaction. The suspensions were dialyzed against DW for 24 hours and then concentrated by centrifuge to 1% weight.

[0147] CNC-MNP composite TEM scan

[0148] The structural features of the CNC-MNP composite suspension were analysed by TEM to assess whether the ferrous oxide nanoparticles are attached to the CNC particles themselves.

[0149] Fig. 8 shows a TEM image of a pure CNC suspension and a TEM image of CNC- MNP composite. The left picture shows CNC particles that are faintly seen on the background of the ultra-thin grid used in the TEM scan. The right side shows CNC particles with small dark spots on the CNC itself and not around it. Furthermore, it is shown that the particles can grow on the CNC themselves and the MNP that do not grow on the CNC particles aggregate to form larger clumps (arrow).

[0150] CNC-MNP composite drying under magnetic field

[0151] Suspension of CNC-MNP composites were concentrated to 1.5wt% by centrifuging at 4000RPM for 1 minute and 20 ml of suspension were cast into 90mm diameter petri dishes. Suspensions of the 5-minute, 10-minute and 15-minute growth time CNC-MNP along with a pure CNC suspension were used. The suspensions were left to evaporate for 48 hours until a constant weight was achieved. An identical set of cast CNC and CNC-MNP composites were left to evaporate under a cylindrical magnet producing 55mT south magnetic field and a 55mT north magnetic field for 48 hours until a constant weight was achieved. Dried CNC and CNC-MNP composite films were placed in an insulating mould between two copper electrodes. The films were connected to the multimeter and using the Instron machine a consistent force of 50N was applied cyclically to the films and recorded.

[0152] Fig. 9 shows the difference between CNC and CNC-MNP voltage output under the same applied force. The pure CNC control shows average volage of around 70mV and the CNC-MNP composite film drying under south oriented magnetic field around has an average voltage of ~150mV. The CNC-MNP composite film drying under north magnetic field did not yield as high a voltage with an average of ~65mV.

[0153] Suspensions of CNC-MNP composites synthesized with different growth times, 5 minutes, 10 minutes, and 15 minutes were mixed with pure CNC at ratios of 1:2, 1:5 and 1:10 of CNC-MNP to Pure CNC. Each suspension was cast into six films, three dried under magnetic field of 55mT south and three films fried under ambient conditions until a constant weight was achieved. Each film was placed between two copper electrodes and struck using an Instron machine a 50 N per strike. The voltage output was recorded and the average voltage peak of five strikes on three films of each batch were averaged and presented in the graph below.

[0154] Fig. 10 shows that the higher the ratio of CNC-MNP composite in comparison to CNC in the films, the higher the average voltage output of the films in all growth times. Films dried under a magnetic field show higher voltage output across all films, where the highest voltage output seems to come from the films with 10-minutes and 15-minutes growth time. Films with 5 minutes growth time show a lower effect from drying under magnetic field.

[0155] Chiral Enhanced Charge Separation and Quantum-Confined Stark Effect in Cellulose Nanocrystal Films

[0156] To further study the impact of the chiral self-organization of the developed hybrid material on charge separation, another device variant was examined. In this variant, a QDs / CNC hybrid film underwent rapid drying in an oven at 80 degrees Celsius for two hours (and without a magnet), thereby preventing the formation of chiral helical order within the dried film. The drying of the QDs / CNC suspension was conducted on an identical SiCh / Ti / Au substrate as the original device (and the measured dry QDs / CNC film thickness was ~1 pm, analogous to the original device). The subsequent fabrication steps mirrored those of the original device, involving the deposition of 30 nm AI2O3, followed by 100 nm indium tin oxide, and a narrow Cr / Au electrode.

[0157] The spectral shift responses of this rapidly dried, ‘non-chiral’ device variant to varying external E-field magnitudes are depicted in Fig. 11. Concurrently, the evolution of the maximum emission peak wavelength (Amax) at each applied bias level (0V, 5V, 10V, 15V) for this variant is illustrated in Fig. 12.

[0158] Summary

[0159] QDs have been embedded in chirally arranged CNC films generating a new hybrid material, enabling formation of excitons with well-defined spin states upon photoexcitation with CPL. Leveraging the spin-filtering capability of the chiral CNC via the CISS effect, a long-lived charge separation was achieved. Both local nanoscale and device-wide microscale charge separation were obtained using a device based on the chiral CNC embedded with the semiconductor QDs and magnetic nanoparticles. It shows sensitivity to circular polarization excitation of the QDs, with significant variations in the QCSE emission peak shifts under an applied electric field. In addition, we report unusually large peak shift magnitudes for an ensemble of spherical QDs. These results are attributed to the CISS effect, enabling efficient room- temperature local charge separation. Moreover, these findings suggest that local separations promote a durable charge separation across the device's length scales, extending beyond 1 pm, even absent an external voltage bias. This effect is explained by a simple theory.

[0160] Leveraging the dielectric and chiral attributes of CNC, the device of the invention exhibits characteristics akin to a supercapacitor. Further, incorporating QDs within the chiral CNC matrix gives rise to a photovoltaic charge-separating device. This research opens avenues for a diverse array of potential applications, from self-assembled devices that combine photovoltaic cells with electric capacitance, to optical electric -field hybrid biosensors and piezoelectric sensors with an enhanced signal-to-noise ratio.

Claims

CLAIMS:

1. A photoexcitable chiral arrangement comprising a chiral assembly of CNC nanorods and quantum dots (QDs), excitable under light to form mobile electron-hole pairs, the arrangement being configured for separating and trapping of electrons and holes in trapping sites within the chiral arrangement.

2. A photoexcitable ordered CNC arrangement comprising CNC nanorods helically oriented around a common axis, the arrangement comprising a distribution of quantum dots (QDs) selected for generating, under light, mobile electron-hole pairs, wherein the arrangement is configured for trapping electrons and holes in trapping sites therewithin.

3. The photoexcitable arrangement according to claim 1 or 2, wherein the light is polarized light.

4. A film of a photoexcitable arrangement according to any one of claims 1 to 3, or implementing an arrangement according to any one of claims 1 to 3.

5. The film according to claim 4, having a thickness between 900nm and 2 microns.

6. The film according to claim 4 or 5, wherein the quantum dots are provided as nanoparticles, as core-shell systems, or as multi-core systems.

7. The film according to claim 6, wherein the quantum dots are of a material selected from a Group II- VI, III-V, III- VI, IV- VI semiconductor material.

8. The film according to any one of claims 4 to 7, wherein the QDs are of a III / V material.

9. The film according to claim 8, wherein the III / V material is selected from InAs, GaAs, GaP, GaSb, InP, InSb, AlAs, A1P, AlSb, InGaAs, GaAsP, and InAsP.

10. The film according to any one of claims 4 to 7, wherein the QDs are of a III / VI material.

11. The film according to claim 10, wherein the III / VI material is selected from InS, ImSs, InSe, ImSes, I Ses, ImSes, InTe, ImSes, GaS, Ga2Se3, GaSe, Ga2Se3, GaTe, Ga2Te3, ImSes-xTex, GaTeSe, and (GaxIni-x)Se3, wherein x is zero or 1.

12. The film according to any one of claims 4 to 7, wherein the QDs are of a II / VI material.

13. The film according to claim 12, wherein the II / VI material is selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdZnSe, CdSSe, and ZnSSe.

14. The film according to any one of claims 4 to 7, wherein the QDs are of a material selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe,HgTe, InAs, InP, InSb, AlAs, A1P, AlSb, InGaP, ZnSeTe, ZnCdS, ZnCdSe, and CdSeS and core- shell forms thereof.

15. The film according to any one of claims 4 to 7, wherein the QDs are core-shell particles of a material selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, A1P, and AlSb.

16. The film according to any one of claims 4 to 7, wherein the QDs are core-shell structures formed of CdSe or ZnS.

17. The film according to claim 16, wherein the QDs are CdSe / ZnS core-shell structures.

18. The film according to any one of claims 4 to 17, comprises blue QDs or red QDs.

19. The film according to any one of claims 4 to 18, wherein the arrangement comprises magnetic nanoparticles.

20. The film according to claim 19, wherein the magnetic nanoparticles are ferrimagnetic, or ferromagnetic.

21. The film according to claim 19 or 20, wherein the magnetic nanoparticles are magnetite (FciCk) or maghemite (gamma-Fe2O3).

22. The film according to claim 19 or 20, wherein the magnetic nanoparticles are formed of a magnetic alloy comprising iron, nickel and / or cobalt.

23. A film comprising a photoexcitable ordered CNC arrangement comprising chirally ordered cellulose nanocrystals (CNC) nanorods helically oriented around a common axis, wherein the arrangement comprises core-shell CdSe / ZnS QDs, and optionally magnetite nanoparticles, wherein the QDs are arranged within the arrangement to provide a measurable capacitance.

24. The film according to any one of claims 4 to 23, implemented as an optical device or in an optical device, an electronic device, or an optoelectronic device.

25. The film according to any one of claims 4 to 23, implemented in a multilayered stacked device comprising one or more additional films of same or different arrangement.

26. The film according to claim 24 or 25, wherein the device is a photovoltaic cell with a built-in capacitor for storing energy.

27. The film according to claim 24, wherein the device is a flexible self-assembled battery.

28. The film according to claim 24, wherein the device is a tunable and flexible stress and optical sensor.

29. The film according to any one of claims 4 to 28, formed on flexible substrate.

30. The film according to any one of claims 4 to 29, formed by spreading.

31. The film according to any one of claims 4 to 30, formed on an external surface of a 3D object.

32. A device comprising a photoexcitable chiral arrangement comprising a chiral assembly of CNC nanorods and quantum dots (QDs), the arrangement being configured so that mobile electron-hole pairs are generated due to incidence of light, and electrons and holes become trapped in trapping sites therewithin.

33. The device according to claim 32, comprising a photoexcitable film or a photoexcitable surface comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods helically oriented around a common axis, wherein the arrangement comprises QDs arranged within the arrangement of chirally ordered CNC to provide charge separation upon excitation with a polarized light and charge storage within the arrangement.

34. The device according to claim 32, the arrangement comprising a distribution of magnetic nanoparticles and QDs, wherein the excitation by a polarized light leads to formation of electron-hole pairs and formation of an electric field gradient along the chiral axis, wherein the electron-hole pair having a spin state corresponding with the polarized light.

35. The device according to any one of claims 32 to 34 being a stacked device comprising two or more photoexcitable films.

36. The device according to claim 35, wherein each of the two or more photoexcitable films comprises a different population of QDs.

37. The device according to any one of claims 32 to 36, arranged as a tandem device.

38. The device according to any one of claims 32 to 37, being a photocapacitor device, an energy storage device or a photovoltaic device.

39. A photocapacitor device comprising a single electronic device comprised of a photoexcitable active layer comprising an arrangement of a plurality of CNC nanorods helically arranged around a common axis, and a plurality of QDs distributed within the arrangement; a metal layer at a first side of the active layer and a metal electrode at a second side of the active layer.

40. A photocapacitor device for responding to a light of a selected polarization, said device comprising an arrangement of a plurality of CNC nanorods helically arrangedaround a common axis, and a plurality of magnetic nanoparticles and QDs distributed within the arrangement; wherein the arrangement is formed on a substrate in the form of a layer or a film.

41. A photovoltaic cell (PV cell), the PV cell comprising a photoexcitable film comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods helically arranged around a common axis, wherein the arrangement comprises QDs such as core-shell CdSe / ZnS QDs, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation and charge storage upon excitation with a polarized light.

42. An energy storage device comprising a photoexcitable film having electronic capacitance, wherein the film comprising an arrangement of chirally ordered cellulose nanocrystals (CNC) nanorods helically arranged around a common axis, wherein the arrangement comprises QDs such as core-shell CdSe / ZnS QDs, wherein the QDs are arranged within the arrangement of chirally ordered cellulose nanocrystals to provide charge separation and charge storage upon excitation with a polarized light.

43. A device comprising a plurality of stacked films of a photoexcitable arrangement according to any one of claims 1 to 3, or implementing an arrangement according to any one of claims 1 to 3.

44. The device according to claim 43 , wherein each arrangement comprises a different QD population.

45. The device according to claim 43, comprising two or more arrangements connected in series, such that a top arrangement is configured to absorb high energy photons and a bottom arrangement is configured to absorb low energy photons.

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