An optoelectronic device

Abstract

This disclosure relates to an optoelectronic device. The optoelectronic device comprises an absorber domain of absorber material configured to absorb light to excite the absorber material into an excited absorber energy level; an acceptor domain of acceptor material, the acceptor material comprising an excited acceptor energy level lower than the excited absorber energy level and comprising an intermediate acceptor energy level lower than the excited acceptor energy level; and an extractor domain of charge extraction material, wherein the excited acceptor energy level and the intermediate acceptor energy level are configured to provide for a transition of a first exciton from the excited acceptor energy level to the intermediate acceptor energy level, and the transition generates a second exciton in the intermediate acceptor energy level; and the extractor domain is configured to extract charge provided by the first exciton and the second exciton.

Description

"An optoelectronic device"Cross-Reference to Related Applications

[0001] The present application claims priority from Australian Provisional Patent Application No 2024901672 filed on 3 June 2024, the contents of which are incorporated herein by reference in their entirety.Technical Field

[0002] This disclosure relates to an optoelectronic device.Background

[0003] Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers. An example of an optoelectronic device is a photovoltaic device, commonly referred to as a solar cell, which is a nonmechanical device that converts sunlight directly into electricity. Photovoltaic devices are typically made from semiconductor materials (such as silicon), which absorb photons from the sun and excites an electron in the material to create an exciton (a bound state of an excited electron and an electron hole (i.e., the absence of an electron)). The excitons then dissociate into free electrons and electron holes, where the electrons reach the cathode (negative electrode), and holes reach the anode (positive electrode), creating a flow of electric current through the external circuit.

[0004] In several types of optoelectronic devices, the management of exciton migration is of great importance. For example, in devices such as a bulk-heterojunction solar cells or organic / inorganic hybrid tandem solar cells, excitons need to be migrated to a particular location of the device for it to work efficiently. For example, in a photovoltaic device, excitons need to be moved towards a donor- acceptor interface (e.g., a barrier between semiconductor materials) in order from them to dissociate.

[0005] However, current optoelectronic devices rely on random exciton motion to bring excitons to a particular location and hence, there is uncertainty in migrating excitons to desirable locations. Moreover, migrating excitons to desirable locations is difficult as excitons can only travel a limited distance (as referred to as the diffusion length) before recombining and losing their energy. Moreover, different excitons (such as excitons in different quantum states) have different diffusion lengths, which adds to the difficulty of managing exciton migration. This restricts the ability to migrate excitons to specific locations within the optoelectronic device which may be advantageous to the performance of the device.

[0006] Moreover, for photovoltaic devices, it is desired to have a material, where photons are absorbed and excitons are generated, with sufficient thickness to absorb more photons from the sun to improve the performance of the photovoltaic device. However, due to the thickness of the material, excitons may recombine and lose their energy before they can dissociate into an electron and electron hole, as the excitons can only travel a limited distance before recombining. This can limit the performance of such optoelectronic devices.

[0007] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

[0008] Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.Summary

[0009] Disclosed herein are embodiments of an optoelectronic device. The embodiments of the optoelectronic device comprise an absorber domain where the absorption of light occurs, and an acceptor domain where excitons are generated. As such, absorption of light (e.g., photons from the sun) and generation of excitons can occur in separate domains. This can be used to manage the migration of excitons to improve the performance of the optoelectronic device. In essence, the embodiments described herein allows for exciton migration management by decoupling the light absorption and other electronic / excitonic processes.

[0010] According to the present disclosure, there is provided an optoelectronic device comprising: an absorber domain of absorber material configured to absorb light to excite the absorber material into an excited absorber energy level; an acceptor domain of acceptor material, the acceptor material comprising an excited acceptor energy level lower than the excited absorber energy level and comprising an intermediate acceptor energy level lower than the excited acceptor energy level; and an extractor domain of charge extraction material, wherein the excited acceptor energy level and the intermediate acceptor energy level are configured to provide for a transition of a first exciton from the excited acceptor energy level to the intermediate acceptor energy level, and the transition generates a second exciton in the intermediate acceptor energy level; and the extractor domain is configured to extract charge provided by the first exciton and the second exciton.

[0011] It is an advantage that the excited acceptor energy level is lower than the excited absorber energy level as the absorption of light by the absorber domain facilitates a transition of the first exciton to the acceptor energy level. This, in turn, facilitates the transition of the first exciton from the excited acceptor energy level to the intermediate acceptor energy level to thereby generate a second exciton. This meansthat the acceptor domain can be thin as it does not need to absorb light, and the generation of a second exciton provides more charge in the extractor domain.

[0012] In some embodiments, the optoelectronic device further comprises an interface of interface material associated with the acceptor domain, the interface being configured to facilitate passivation and tunnelling of the first exciton and the second exciton from the acceptor domain to the extractor domain.

[0013] In some embodiments, the interface is patterned to facilitate passivation and tunnelling of the first exciton and the second exciton from the acceptor domain at one or more specific locations in the extractor domain.

[0014] In some embodiments, the interface is patterned in a tessellating pattern.

[0015] In some embodiments, the interface is formed by atomic layer deposition.

[0016] In some embodiments, the interface material is one of: tin oxide; hafnium oxide; titanium oxide; zinc oxide; aluminium oxide; and amorphous silicon.

[0017] In some embodiments, the optoelectronic device comprises multiple absorber domains, each of the multiple absorber domains being configured to absorb light of a different wavelength to excite the absorber material into a different excited absorber energy level.

[0018] In some embodiments, the multiple absorber domains are configured to form an energy cascade.

[0019] In some embodiments, the intermediate acceptor energy level is an energy level of a triplet state.

[0020] In some embodiments, the excited absorber energy level and the excited acceptor energy level are an energy level of a singlet state.

[0021] In some embodiments, the energy level of the singlet state is about twice the energy level of the triplet state.

[0022] In some embodiments, the first exciton undergoes singlet fission to generate the second exciton in the intermediate acceptor energy level.

[0023] In some embodiments, the first exciton occurs on a first molecule of the acceptor material and the second exciton occurs on a second molecule of the acceptor material.

[0024] In some embodiments, the charge extraction material comprises silicon.

[0025] In some embodiments, the absorber material is one or more of: an organic small molecule; a polymeric dye; a quantum dot; a quantum well superstructure; a quantum well superlattice; and a perovskite material.

[0026] In some embodiments, the acceptor material is a chromophore.

[0027] In some embodiments, the acceptor domain is disposed between the absorber domain and the extractor domain; and the interface is disposed between the acceptor domain and the extractor domain.

[0028] In some embodiments, the optoelectronic device is a photovoltaic device.

[0029] In some embodiments, the absorber domain, the acceptor domain and the extractor domain are layers.Brief Description of Drawings

[0030] An example will be described with reference to the following drawings:

[0031] Fig. la illustrates an optoelectronic device according to a one embodiment.

[0032] Fig. lb illustrates an expanded view of the optoelectronic device of Fig. la.

[0033] Fig. 2 illustrates the energy levels and exciton generation in the optoelectronic device of Fig. la, which is representative of an energy level diagram.

[0034] Fig. 3 illustrates the process of charge extraction in the optoelectronic device of Fig. la.

[0035] Fig. 4 illustrates an embodiment of the optoelectronic device with multiple absorber domains.

[0036] Fig. 5a illustrates an embodiment of the optoelectronic device, which comprises an interface of interface material.

[0037] Fig. 5b illustrates an expanded view of the optoelectronic device of Fig. 5a.

[0038] Fig. 6a illustrates an embodiment of the optoelectronic device comprising a patterned interface.

[0039] Fig. 6b illustrates the optoelectronic device of Figs. 5a-b, in which interface is patterned differently to the patterned interface of Fig. 6a.

[0040] Fig. 7 illustrates example tessellating patterns.

[0041] Fig. 8 illustrates a preferred embodiment of the optoelectronic device.

[0042] Fig. 8b illustrates a side view of the preferred embodiment of the optoelectronic device.

[0043] Fig. 8c illustrates the process of exciton injection in the extractor domain of the preferred embodiment of the optoelectronic device.

[0044] It is noted that the drawings presented herein are only from illustrative purposes. In particular, the embodiments of the optoelectronic depicted in the drawings are not necessary drawn to scale. Moreover, the thickness of domains is not necessarily representative of the relative thickness of the domains.Description of Embodiments

[0045] Disclosed herein are embodiments of an optoelectronic device, particularly directed towards managing the migration of excitons. Moreover, the disclosed embodiments enable multiple exciton generation and hence, the disclosed embodiments are directed towards facilitating multiple exciton generation in an optoelectronic device to improve the performance of the optoelectronic device. For example, if the optoelectronic device is a photovoltaic device, then multiple exciton generation could improve the photoconversion efficiencies. Hence, more electricity could be generated from the same incident sunlight.

[0046] As will be discussed, managing exciton migration and multiple exciton generation in an optoelectronic device can be facilitated by the specific arrangement of material domains that form the optoelectronic device, as well as the specific material used to form the material domains and patterning of the material domains. In particular, an acceptor material is chosen to have the desired properties for multiple exciton generation. More specifically, the acceptor material is chosen to have an excited acceptor energy level lower than the excited absorber energy level of the absorber material that forms the absorber material. Importantly, the acceptor material is chosento have an intermediate acceptor energy level lower than the excited acceptor energy level, where the intermediate acceptor energy level facilitates multiple exciton generation. It is noted that it is difficult to find materials with this property.

[0047] The optoelectronic device and the embodiments described herein may be fabricated by stepwise deposition of materials, using self-assembled macromolecules, nanoparticles, or through MOFs (metal-organic frameworks). The optoelectronic device and the embodiments described herein may be fabricated by other deposition techniques such as chemical vapor deposition (CVD), atomic layer deposition (ALD), as well as lithography techniques, such as electron beam lithography, photolithography and nano sphere lithography.

[0048] It is noted that this disclosure is directed towards the optoelectronic device being a photoelectronic device (i.e., a solar cell). However, the optoelectronic device and the embodiments thereof are not limited to being a photoelectronic device. The optoelectronic device disclosed herein may also be a light emitting device (LED), such as an organic light-emitting devices (OLEDs) and quantum dot LEDs (QLEDs). The optoelectronic device may also be, but not limited to, a laser diode, photodiode, phototransistor and an optocoupler.

[0049] Fig. la illustrates optoelectronic device 100 according to one embodiment. Fig. lb illustrates an expanded view of optoelectronic device 100 of Fig. la. Optoelectronic device 100 comprises absorber domain 110 of absorber material. In other words, absorber domain 110 is formed from absorber material. Absorber domain 110 may be where photons are absorbed, such as photons from solar radiation incident on optoelectronic device 100. In other words, absorber domain 110 may be where energy from incident photons is converted. The absorber material may be one or more of, but not limited to, an organic small molecule; a polymeric dye; a quantum dot; a quantum well superstructure (such as gallium arsenide); a quantum well superlattice (which may be similar to a quantum well superstructure); and a perovskite material. Absorber material may also be a chromophore (i.e., a molecule that absorbs particular wavelengths of visible light) or a fluorophore (similar to a chromophore). In someembodiments, optoelectronic device 100 may comprise multiple absorber domains, as will be discussed in a later embodiment.

[0050] Optoelectronic device 100 comprises acceptor domain 120 of acceptor material. Acceptor domain 120 may be where excitons are generated. Acceptor domain 120 may be configured to receive or absorb energy (in the form of photons, for example) from absorber domain 110, or other sources of light (such as the sun). The acceptor material may be formed from a chromophore or a fluorophore. For example, the acceptor material may be an acene, pentacene, tetracene (which may be referred to as naphthacene) or derivations and / or variations thereof (e.g., with alternative side chains, dimers etc). The acceptor material may also be formed from dipyrrolonaphthyridinedione (DPND) or derivations and / or variations thereof (e.g., with alternative side chains, dimers etc). In some embodiments, optoelectronic device 100 may comprise multiple acceptor domains.

[0051] Optoelectronic device 100 comprises extractor domain 130 of charge extraction material. In some embodiments, the charge extraction material comprises silicon. However, the charge extraction material is not limited to silicon and may be another semiconductor material, for example. Extractor domain 130 is configured to extract charge provided by excitons generated in acceptor domain 120. For example, electrons, originating from the exciton dissociation, may reside in extractor domain 130. Extractor domain 130 may be also configured to extract energy provided by excitons generated in acceptor domain 120. Extractor domain 130 may be also configured to absorb photons and generate excitons, which may dissociate within extractor domain 130 to form free electrons and free electron holes. Optoelectronic device 100 may further comprise one or more electrodes (not shown) which are configured to accept electrons residing in extractor domain 130 and / or accepted electron holes originating from the exciton dissociation, to facilitate the flow of an electrical current. In some embodiments, optoelectronic device 100 may comprise multiple extractor domains.

[0052] It is noted that reference to “domain” in this disclosure refers to any shaped volume or region occupied by the respective material. For example, as depicted in Fig. lb, absorber domain 110, acceptor domain 120 and extractor domain 130 are layers. In particular, absorber domain 110, acceptor domain 120 and extractor domain 130 may be of a particular thickness for optimal performance of optoelectronic device 100. For example, absorber domain 110 and acceptor domain 120 may be between 20nm and 40nm. In another example, any of the absorber domain 110 and acceptor domain 120 may be a few nanometres thick or a few molecules thick. In some examples, extractor domain 130 may be much thicker in comparison to absorber domain 110 and acceptor domain 120. For example, absorber domain 110 and acceptor domain 120 may be in a nanometre scale, whereas extractor domain 130 may be micron scale. In a more specific example, absorber domain 110 and acceptor domain 120 may be between 20nm and 40nm, whereas extractor domain 130 may be between 100pm and 200pm.

[0053] However, it is noted that absorber domain 110, acceptor domain 120 and extractor domain 130 are not limited to being layers. For example, absorber domain 110, acceptor domain 120 and extractor domain 130 may be patterned layers and may resemble cubes or other shaped structures. For example, absorber domain 110, acceptor domain 120 and extractor domain 130 may be concentric rings or circles. Further, any of the domains discussed herein may also comprise disconnected regions of the domain material. As such, the domains discussed herein are not necessarily continuous (i.e., forming an unbroken whole; without interruption) as depicted in Figs, la and lb.

[0054] In some embodiments, acceptor domain 120 is disposed between absorber domain 110 and extractor domain 130, as depicted in Figs, la and lb. However, alternate embodiments are equally possible. For example, in one embodiment, extractor domain 130 is disposed between absorber domain 110 and acceptor domain 120. The arrangement of absorber domain 110, acceptor domain 120 and extractor domain 130 may be dependent on the type of optoelectronic device. For example, a photovoltaic device may have a different arrangement of absorber domain 110, acceptor domain 120 and extractor domain 130, when compared to a LED.

[0055] Fig. 2 illustrates the energy levels and exciton generation in optoelectronic device 100. Fig. 2 is representative of an energy level diagram. Absorber material, which forms absorber domain 110, comprises excited absorber energy level 211 as well as absorber ground state energy level 212. It is noted that in this disclosure, the reference to “energy level” refers to the energy of a quantum state of a particle (such as a molecule). Particles usually have a most stable quantum state, which may be referred to as the ground state, and hence, the energy level of the ground state may correspond to the lowest possible energy of the particle. Particles usually have one or more excited states which are of a higher energy than the ground state but are usually more unstable when compared to the ground state. In this disclosure, “energy level” is indicative of a corresponding quantum state. The quantum states and hence, the corresponding energy levels, are a property (and hence, indicative) of the particles (i.e., the molecules) of the respective material.

[0056] Absorber domain 110 is configured to absorb light (such as photon 241, which may originate from the sun or another light source) to excite the absorber material into excited absorber energy level 211. More specifically, photon 241 may excite the absorber material (e.g., a molecule of the absorber material) from absorber ground state energy level 212 (i.e., the most stable energy state of the absorber material) into excited absorber energy level 211. As such, the energy of photon 241 may correspond approximately to the energy difference (which may be referred to as the energy gap) between excited absorber energy level 211 and absorber ground state energy level 212. Excited absorber energy level 211 may be an energy level of an excited state of an energy level of a metastable state.

[0057] Acceptor material, which forms acceptor domain 120, comprises excited acceptor energy level 221 lower than excited absorber energy level 211. “Lower” in the context of the present disclosure may refer to the energy gap between the ground state and the excited state being less, smaller or the like in comparison. Similar to absorber material, acceptor material also comprises acceptor ground state energy level 222. Absorber ground state energy level 212 and acceptor ground state energy level 222 may be of a similar energy level. However, absorber ground state energy level 212 andacceptor ground state energy level 222 may be slightly different given the differences in the absorber material and the acceptor material.

[0058] Acceptor material also comprises intermediate acceptor energy level 223, which is lower than excited acceptor energy level 221 and hence, lower than excited absorber energy level 211. In some embodiments, intermediate acceptor energy level 223 may be about half of the energy of excited acceptor energy level 221 (i.e., excited acceptor energy level 221 may be twice the energy of intermediate acceptor energy level 223). It is noted that it is difficult to find a molecule or material that has an intermediate energy level at or below half of an excited acceptor energy level. Such a molecule or material may be useful, as will be discussed.

[0059] Acceptor ground state energy level 222 and intermediate acceptor energy level 223 may be an energy level of an excited state of an energy level of a metastable state. Preferably, intermediate acceptor energy level 223 is an energy level of a metastable state. A metastable state is an excited state of a molecule that has a longer lifetime than the ordinary excited states and that generally has a shorter lifetime than the lowest, often stable, ground state.

[0060] Excited acceptor energy level 221 and intermediate acceptor energy level 223 are configured to provide for a transition of first exciton 251 from excited acceptor energy level 221 to intermediate acceptor energy level 223, and the transition generates second exciton 252 in intermediate acceptor energy level 223. This may be referred to as multiple exciton generation, as second exciton 252 is generated in acceptor domain 120 as a result of first exciton 251 transitioning to intermediate acceptor energy level 223. This is beneficial in optoelectronic devices, such as photovoltaic devices, as photon 241 is able to generate essentially twice the number of electrons in extractor domain 130 as a result of the generation of second exciton 252.

[0061] With reference to Fig. 2, an example of the multiple exciton generation process is now explained in more detail. Photon 241 may excite the absorber material from absorber ground state energy level 212 into excited absorber energy level 211.More specifically, photon 241 may excite a molecule in the absorber material from absorber ground state energy level 212 into excited absorber energy level 211. The molecule may then relax into absorber ground state energy level 212 thereby emitting photon 242. Acceptor domain 120 may then receive, accept, or absorb photon 242. More specifically, molecule 261 (represented by the dashed box) may absorb photon 242 to generate first exciton 251 in excited absorber energy level 211.

[0062] In some embodiments, the absorber material and the acceptor material may interact without the exchange of a real photon. More specifically, molecules in absorber domain 110 may interact with molecules of acceptor domain 120. In other words, in some embodiments, photon 242 may not be a real photon. In some embodiments, the absorber material and the acceptor material may interact by transferring energy through nonradiative dipole-dipole coupling. As such, photon 242 may be a virtual photon, rather than a real photon. Virtual photons may be referred to as “virtual” because they do not exist as free particles in the traditional sense but instead serve as intermediate particles in the exchange of force or energy between other particles. This process may be referred to as Forster resonance energy transfer (FRET), fluorescence resonance energy transfer, resonance energy transfer (RET) or electronic energy transfer (EET).

[0063] FRET is analogous to near-field communication, in that the radius of interaction is much smaller than the wavelength of light emitted. In the near-field region, the excited molecule in the absorber material (such as a chromophore) emits a virtual photon that is instantly absorbed by a molecule in the acceptor material (such as a receiving chromophore). These virtual photons are undetectable, since their existence violates the conservation of energy and momentum, and hence FRET is known as a radiationless mechanism. As such, absorber domain 110 and acceptor domain 120 may be configured to establish a FRET interaction between the absorber material and the acceptor material.

[0064] Molecule 261 may then interact with an adjacent molecule of the acceptor material (i.e., molecule 262). As will be appreciated, molecule 261 and molecule 262 have the same energy levels (i.e., excited acceptor energy level 221, acceptor groundstate energy level 222 and intermediate acceptor energy level 223). Molecule 261 may interact with molecule 262 by an energy transfer process, for example. More specifically, molecule 261 may interact with molecule 262 by a FRET process, for example. The interaction between molecule 261 and molecule 262 results in first exciton 251 transitioning from excited acceptor energy level 221 to intermediate acceptor energy level 223 and second exciton 252 being generated in intermediate acceptor energy level 223. Although the multiple exciton generation is described with reference to first exciton 251 and second exciton 252, it is noted that many excitons may be generated in acceptor domain 120 through this process. In other words, in practice, there are more than two excitons in acceptor domain 120.

[0065] In some embodiments, excited absorber energy level 211 and excited acceptor energy level 212 are an energy level of a singlet state. A singlet state of a molecule refers to a quantum state where all electrons in the molecule are spin paired. Moreover, in some embodiments, intermediate acceptor energy level 223 is an energy level of a triplet state. A triplet state of a molecule refers to a quantum state which contains unpaired electrons and hence, the spin of the unpaired electrons can be parallel as they are not required to follow the Pauli Exclusion Principle. It is noted that the triplet state of most molecules is more stable than the respective singlet state. Therefore, there is an advantage in transitioning molecules to the triplet state.

[0066] In some embodiments, first exciton 251 undergoes singlet fission to generate second exciton 252 in intermediate acceptor energy level 223. More specifically, first exciton 251 which may be a singlet state exciton after molecule 261 absorbs photon 242, undergoes fission to produce two triplet state excitons (i.e., first exciton 251 in intermediate acceptor energy level 223 and second exciton 252 in intermediate acceptor energy level 223). In some examples, the energy level of the singlet state is about twice the energy level of the triplet state. It is noted that “singlet state exciton” or “exciton in a singlet state” refers to the molecule of the acceptor material (e.g., molecule 261) in the corresponding quantum state. This is similar for “triplet state exciton” or “exciton in a triplet state.” In essence, an exciton can be thought of as an excited state of a molecule of the acceptor material.

[0067] Singlet fission is a spin-allowed process, where molecule 261 and molecule 262 (which may be chromophores, for example) are oriented such that the electronic coupling between singlet and the double triplet states is large. As such, in some embodiments, the acceptor material is configured to facilitate singlet fission within acceptor domain 120. Being spin allowed, the process can occur very rapidly (on a picosecond or femtosecond timescale) and out-compete radiative decay (that generally occurs on a nanosecond timescale) thereby producing two triplets with very high efficiency. As such, there is an advantage in first exciton 251 undergoing singlet fission to generate second exciton 252, due to the very rapid generation with high efficiency. The process is distinct from intersystem crossing, in that singlet fission does not involve a spin flip but is mediated by two triplets coupled into an overall singlet. However, in some embodiments, the acceptor material is configured to facilitate intersystem crossing within acceptor domain 120 to generate triplet state excitons. It is noted that that some acceptor materials are better configured to facilitate singlet fission and hence, may be referred to as singlet fission material.

[0068] Molecule 261 and molecule 262 may be chromophores and, hence, intramolecular singlet fission may occur to generate second exciton 252. Typically, the mechanisms for singlet fission are classified into (a) direct coupling between the molecules and (b) stepwise one-electron processes involving the charge-transfer states. Intermolecular interactions and the relative orientation of the molecules within the aggregates may also affect the singlet fission efficiencies.

[0069] It is noted that excitons in singlet states can travel further than excitons in triplet states and hence, excitons in singlet states are more mobile than excitons in triplet states. In other words, excitons in singlet states have a greater diffusion length than excitons in triplet states. Therefore, it is preferable to have a thin domain when multiple exciton generation (e.g., singlet fission) occurs (i.e., acceptor domain 120), so that the generated excitons in the triplet states can easily transverse acceptor domain 120 and dissociate. More specifically, having a thin domain enables the triplet states to easily reach the interface between acceptor domain 120 and extractor domain 130 (i.e., the barrier between acceptor domain 120 and extractor domain 130) to facilitate excitondissociation. Such preference is achievable with optoelectronic device 100, as the singlet excitons can be generated in absorber domain 110 while the triplet excitons can be generated in acceptor domain 120. As such, absorber domain 110 can be thick to absorb more light (such as photons from the sun in the case of optoelectronic device 100 being a photovoltaic device) and acceptor domain 120 can be thin, so that the triplet excitons can easily reach the interface between acceptor domain 120 and extractor domain 130.

[0070] Fig. 3 illustrates the process of charge extraction in optoelectronic device 100. As explained previously with reference to Fig. 2, incident photon 241 may cause absorber material to emit photon 242, which is then absorbed by the acceptor material. Again, it is noted that photon 242 may be a virtual in the case where molecules of absorber material interact with molecules of acceptor material via a FRET process, for example. Absorption of photon 242 in the acceptor material may cause multiple exciton generation in acceptor domain 120. More specifically, the absorption of photon 242 by acceptor material generates first exciton 251 and second exciton 252 in acceptor domain 120. First exciton 251 and second exciton 252 then move toward interface 310, which is the interface (i.e., the boundary) between acceptor domain 120 and extractor domain 130. First exciton 251 and second exciton 252 then diffuse into extractor domain 130, which results in first exciton 251 and second exciton 252 dissociating into a free electron and an electron hole. For example, first exciton 251 dissociates into electron 321 and electron hole 322. Optoelectronic device 100 may further comprise one or more electrodes (not shown) which are configured to accept electrons residing in extractor domain 130 and / or accepted electron holes originating from the exciton dissociation, to facilitate the flow of an electrical current.

[0071] Fig. 4 illustrates an embodiment of the optoelectronic device with multiple absorber domains. More specifically, Fig. 4 illustrates optoelectronic device 400 with three absorber domains 410, 420, 430. However, it is noted that this is only an example of optoelectronic device 400 and optoelectronic device 400 may comprise more or less than three absorber domains. Absorber domains 410, 420, 430 may each be formed from a similar or different absorber material. Absorber domains 410, 420, 430 are eachsimilar to absorber domain 110 described with reference to Figs. 1-3. Optoelectronic device 400 also comprises acceptor domain 440 and extractor domain 450, which are similar to acceptor domain 120 and extractor domain 130, respectively, described with reference to Figs. 1-3 (i.e., acceptor material comprises excited acceptor energy level 441, acceptor ground state energy level 442 and intermediate acceptor energy level 443).

[0072] Preferably, absorber domains 410, 420, 430 may be relatively thick, while acceptor domain 440 may be relatively thin. This is so absorber domains 410, 420, 430 may absorb more photons and the multiple excitons generated in acceptor domain 440 (i.e., multiple excitons 444) can easily reach the interface between acceptor domain 440 and extractor domain 450 to dissociate before recombining. For example, each of absorber domains 410, 420, 430 may be between 20nm to 40nm. In another example, the thickness of absorber domains 410, 420, 430 may have a combined thickness of between 80nm and 120nm.

[0073] In some embodiments, each of absorber domains 410, 420, 430 may be configured to absorb light of a different wavelength. More specifically, each of absorber domains 410, 420, 430 may be configured to absorb light of a different wavelength to excite the absorber material into a different excited absorber energy level. In more detail, absorber domains 410, 420, 430 comprise excited absorber energy level 411, 421, 431 and absorber ground state energy level 412, 422, 432. Absorber ground state energy levels 412, 422, 432 may be of a similar energy (noting that the ground state energy levels may be slightly different, due to the differences in the absorber materials), but excited absorber energy levels 411, 421, 431 are of different energies. The different excited absorber energy levels 411, 421, 431 may be indicative of the different materials used to form absorber domains 410, 420, 430. As each of the absorber domains are configured to absorb a different wavelength of light, the overall absorber domain (comprised of the individual absorber domains) can absorb a broader spectrum of light and hence, enhances the bandwidth of optical absorption of optoelectronic device 400. In other words, optoelectronic device 400 is sensitive ofmultiple different wavelengths of light. Hence, this improves the performance of optoelectronic device 400.

[0074] While the excited absorber energy levels 411, 421, 431 are of different energies, improve the performance of optoelectronic device 400. For example, absorber domains 410, 420, 430 may be arranged based on the energy levels in the adjacent domains. In some embodiments, absorber domains 410, 420, 430 are configured to form an energy cascade. More specifically, absorber domains 410, 420, 430 are arranged such that the as they approach acceptor domain 440. Preferably, the energy cascade also comprises excited acceptor energy level 441, such that excited absorber energy levels 411, 421, 431, 441 descend in energy. In this disclosure, “energy cascade” refers to the energy gap between the energy levels in adjacent materials becoming narrower. Preferably, the excited energy levels in the energy cascade are monotonic decreasing, meaning that the excited energy levels always decrease in subsequent domains.

[0075] As shown in Fig. 4, absorber domains 410, 420, 430 are arranged to form an energy cascade, where excited absorber energy level 421 is lower than excited absorber energy level 411, and energy level 431 is lower than excited absorber energy level 421. It is noted that in other embodiments, optoelectronic device 400 may have more absorber domains, which may also be arranged to form an energy cascade, such that the excited energy levels of adjacent materials decrease. The energy cascade facilitates the multiple exciton generation in acceptor domain 440. More specifically, energy cascade enables the energy to be directed or “funnelled” towards acceptor domain 440. This can be used to generate excitons are specific locations in acceptor domain 440 that are desirable for the performance of optoelectronic device 400.

[0076] It is noted that, in some examples, ground state energy levels 412, 422, 432, 442 may be of different energies, due to the differences between the materials. Therefore, to form an energy cascade, absorber domains 410, 420, 430, as well as acceptor domain 440 may be configured so that the energy gap (i.e., the difference between the ground state energy level and the excited energy level) decreases and fallsentirely within the energy gap of the previous domain (i.e., the previous energy gap overlaps the subsequent energy gap).

[0077] In optoelectronic device 400, the absorber material of absorber domains 410, 420, 430 may interact by a FRET process. In other words, photons 413, 423 may be virtual photons. Similarly, the absorber material of absorber domain 430 may interact with the acceptor material of acceptor domain 440 by a FRET process, as similarly described previous with reference to Fig. 2. Hence, photon 433 may be a virtual photon. As such, the energy cascade depicted in Fig. 4 may be referred to as a FRET cascade. Optoelectronic device 400 may be referred to as a “FRET funnel”, given that energy cascade enables the energy to be directed or “funnelled” towards acceptor domain 440. The FRET cascade can be used to generate multiple excitons 444 in an intermediate acceptor energy level 443 of acceptor domain 440.

[0078] As previously mentioned, in some embodiments, the optoelectronic device disclosed herein may comprise multiple acceptor domains. One or more of the multiple acceptor domains may comprise an acceptor material similar or equivalent to the acceptor material previously described (e.g., the acceptor material may facilitate the generation of a second exciton). However, in some examples, the acceptor domain adjacent to the extractor domain may not necessarily facilitate the generation of a second exciton. Rather, the acceptor domain adjacent to the extractor domain may be configured to enable a first and / or second exciton to traverse through the respect acceptor domain. In particular, the acceptor domain adjacent to the extractor domain may be configured to direct the first and / or second exciton towards the extractor domain to facilitate charge extraction in the extractor domain. In some embodiments, the acceptor domain adjacent to the extractor domain may facilitate passivation from one or more of the acceptor domains at one or more locations in the extractor domain.

[0079] Fig. 5a illustrates an embodiment of the optoelectronic device. More specifically, Fig. 5a illustrates optoelectronic device 500, which comprises interface 530 of interface material. Optoelectronic device 500 comprises absorber domains 510, acceptor domain 520 and extractor domain 540, which are similar or equivalent toabsorber domain 110, acceptor domain 120 and extractor domain 130, respectively, as described with reference to Figs. 1-3. In essence, optoelectronic device 500 is similar or equivalent to optoelectronic device 100 depicted in Figs. 1-3 with interface 530. Fig. 5b illustrates an expanded view of optoelectronic device 500. Similar to optoelectronic device 400 of Fig. 4, optoelectronic device 500 may also comprises multiple absorber domains. Optoelectronic device 500 may also comprise multiples of other domains, in some examples.

[0080] Interface 530 may be associated with acceptor domain 520, such as being deposited on acceptor domain 520. Moreover, interface 530 may be associated with extractor domain 540, such as being deposited on extractor domain 540. In this sense, interface 530 may be disposed between acceptor domain 520 and extractor domain 540. However, alternate arrangements of the domains of optoelectronic device 500 are equally possible. Interface 530 may be configured to facilitate passivation and / or tunnelling of first exciton 251 and second exciton 252 from acceptor domain 520 to extractor domain 540. “Passivation” refers to the process of preventing first exciton 251 and second exciton 252 from recombing into a ground state electron in extractor domain 540. In other words, passivation prevents recombination in extractor domain 540: (1) for charge carriers in extractor domain 540 that were created by exciton transfer from acceptor domain 520, or (2) for charge carriers generated in extractor domain 540 by absorbing a photon. Interface 530 may also be configured to facilitate passivation and / or tunnelling of charges (such as charge carriers) from acceptor domain 520 to extractor domain 540.

[0081] In some embodiments, interface 530 may be formed using a chemical vapour deposition (CVD) process. More specifically, interface 530 may formed by atomic layer deposition (ALD), which is a subclass of CVD. As such, interface 530 may be referred to as an ALD domain. ALD is a thin-film deposition technique based on the sequential use of a gas-phase chemical process. The majority of ALD reactions use two chemicals called precursors (also called “reactants”). These precursors react with the surface of a material one at a time in a sequential, self-limiting, manner. A thin film is slowly deposited through repeated exposure to separate precursors. In someembodiments, the interface material is a metal oxide. For example, the interface material is one of, but not limited to: tin oxide; hafnium oxide, titanium oxide, zinc oxide, aluminium oxide and amorphous silicon.

[0082] In some embodiments, interface 530 is a thin layer of interface material. For example, interface 530 may be a few nanometres thick, or may be a few molecules thick. Having interface 530 as a thin layer of interface material facilitates tunnelling of the excitons into extractor domain 540, as the potential barrier is smaller as compared to a thick material layer. Having interface 530 as a thin layer of interface material is preferable when interface 530 is disposed between acceptor domain 520 and extractor domain 540. However, it is noted that, in some embodiments, interface 530 may not be disposed between acceptor domain 520 and extractor domain 540. As such, in some embodiments, it is advantageous to have interface 530 as a thick material layer to improve performance of optoelectronic device 500.

[0083] In some embodiments, interface 530 is patterned. For example, Fig. 6a illustrates an embodiment of the optoelectronic device comprising a patterned interface 530. More specifically, Fig. 6a illustrates optoelectronic device 500 of Fig. 5, in which interface 530 is patterned. Fig. 6b illustrates optoelectronic device 500 of Figs. 5a-b, in which interface 530 is patterned differently to the patterned interface 530 of Fig. 6a.

[0084] Interface 530 is patterned in Figs. 6a-b to facilitate passivation and / or tunnelling of first exciton 251 and second exciton 252 from acceptor domain 520 at one or more specific locations in extractor domain 540. For example, and with reference to Fig. 6a, as interface 530 is configured to facilitate passivation and / or tunnelling of excitons from acceptor domain 520, excitons generated in acceptor domain 520 may only tunnel into extractor domain 540 where there exists interface material. In other words, excitons move down in the direction of the domains and may only tunnel where there is interface material. As such, one may control the injection of excitons into the extractor domain 540 as a result of the patterning of interface 530. In other words, the patterning of interface 530 enables the spatial control of exciton migration.

[0085] In particular, patterning interface 530 is one dimension (as depicted in Fig. 6a) enables the control of the injection of excitons in two dimensions (i.e., in the direction of the injection / tunnelling and in the direction of the pattern). Moreover, patterning interface 530 is two dimensions (as depicted in Fig. 6b) enables the control of the injection of excitons in three dimensions (i.e., in the direction of the injection / tunnelling and in the two directions along the plane defined by interface 530). Controlling the injection / tunnelling of the excitons from acceptor domain 520 to extractor domain 540 is advantageous, as the excitons can be placed at specific locations in extractor domain 540 to increase the performance of optoelectronic device 500.

[0086] In these embodiments, interface 530 comprises regions 551, 552, 553 corresponding to the pattern. In some embodiments, regions 551, 552, 553 may be spanned by material other than the interface material. For example, regions 551, 552, 553 may be spanned by acceptor material, charge transfer material, charge extraction material or a combination thereof. The reference to “patterned” in this disclosure does not necessarily refer to a design made from repeated shapes, for example. The reference to “patterned” in this disclosure refers to any design. For example, as depicted in Fig. 6a, the “pattern” in which interface 530 is patterned with a trough that extends through the interface 530. Interface 530 may be patterned using ALD, nanoimprinting, a lithography mask, or other lithography techniques.

[0087] In some embodiments, interface 530 may be patterned in a repeating pattern of the same or different shapes. The repeating pattern of the same or different shapes may be connected or disconnected. In some examples, interface 530 may be patterned in a tessellating pattern. A tessellating pattern is a pattern using one or more geometric shapes with no overlaps and no gaps. Example tessellating patterns are illustrated in Fig. 7. However, other tessellating patterns are possible. The examples illustrate in Fig. 7 show possible patterns of interface 530, where some shapes in the tessellating pattern may correspond to the interface material and some shapes may correspond to other materials (such as acceptor material, charge transfer material, charge extraction material or a combination thereof). The shapes in the tessellating pattern correspondingto the interface material may itself be a pattern. Similar is possible for the shapes corresponding to other materials.

[0088] In some examples, the dimensions (i.e., the size) of the shapes in the tessellating pattern or the spacing between the shapes may related to the energy transfer ranges in absorber domain 510 and acceptor domain 520. As such, the dimensions of the shapes or the spacing between shapes in the tessellating pattern may be smaller than the wavelength of light (e.g., light in the visible spectrum). Hence, the tessellating pattern may be used to establish a photonic structure that facilitates (in other words, promotes) the absorption of light in absorber domain 510 or acceptor domain 520.

[0089] In some embodiments, one or more of absorber domain 510, acceptor domain 520 and interface 530 may be patterned. For example, acceptor domain 520 and interface 530 may be patterned with the same corresponding pattern. In another example, acceptor domain 520 and interface 530 may be patterned with opposite patterns, such that acceptor domain 520 fits within the regions defined by the pattern of interface 530. For example, and with reference to Fig. 6a, acceptor domain 520 may be patterned to resemble region 551 to fit within the patterned interface 530. In essence, one or more of absorber domain 510, acceptor domain 520 and interface 530 may be patterned to enhance the properties of optoelectronic device 500 to thereby, improve the performance of optoelectronic device 500.

[0090] Fig. 8 illustrates a preferred embodiment of the optoelectronic device. Fig. 8a illustrates a top view of the preferred embodiment of optoelectronic device 500 (without view of absorber domain 510). In the preferred embodiment, interface 530 is a tessellating pattern. More specifically, interface 530 is patterned with a pattern of repeating squares. In the preferred embodiment, the regions defined by the repeating squares are spanned by acceptor material. In other words, acceptor material fills the gaps (i.e., missing regions) of the patterned interface 530. As such, the repeating squares form the acceptor domain 520 and hence, the acceptor domain 520 is also patterned in this embodiment. Preferably, acceptor domain 520 resembles nanoparticles of acceptor material (i.e., each of the repeating squares may be a nanoparticle ofacceptor material). Preferably, the repeating squares are reasonably spaced to improve the performance of optoelectronic device 500. In some examples, absorber material may also fill the regions missing from the patterned interface 530, so that to directed or “funnel” energy absorbed from incident photons to acceptor domain 520.

[0091] Fig. 8b illustrates a side view of the preferred embodiment of optoelectronic device 500. As discussed above, acceptor domain 520 and interface 530 are patterned in this embodiment, such that acceptor domain 520 is disposed between interface 530, as well as absorber domain 510 and extractor domain 540. The preferred embodiment also comprises a charge transfer domain 550 of a charge transfer material that is patterned with a similar pattern to acceptor domain 520 and is disposed between acceptor domain 520 and extractor domain 540. Charge transfer domain 550 may facilitate the sequential charge transfer from acceptor domain 520 to extractor domain 540. As such, charge transfer domain 550 may either enable an exciton transfer or a sequential charge transfer (e.g. electron and then hole) from acceptor domain 520 to extractor domain 540. In essence, the charge transfer material may be a passivation material similar to interface material. In other words, charge transfer domain 550 may perform a similar function to interface 530. It is noted that other embodiments of the optoelectronic device disclosed herein may also comprise a charge transfer domain.

[0092] It is further noted that interface material may be similar or a different material to charge transfer material. In the preferred embodiments, the interface material is the better passivating material as compared to charge transfer material. Moreover, in the preferred embodiment, charge transfer domain 550 is thinner in comparison to interface 530 and allows for triplet exciton transfer, or sequential charge transfer from acceptor domain 520 to extractor domain 540.

[0093] Fig. 8c illustrates the process of exciton injection in extractor domain 540 in the preferred embodiment of optoelectronic device 500. In the preferred embodiment, photons 560 incident on absorber domain 510 are absorbed and energy is transferred to acceptor domain 520 to generate multiple excitons 570. As a result of the patterning of interface 530, multiple excitons 570 generated in acceptor domain 520 areinjected / tunnel straight down into extractor domain 540. In other words, interface 530 facilitates to tunnelling or injection of multiple excitons 570 into extractor domain 540. Interface 530 also passivates extractor domain 540 to prevent recombination of multiple excitons 570, which is also further facilitates by the patterning of interface 530. In other words, as a result of the patterning of the domains, excitons are directed or “injected” or “pinholed” into extractor domain 540 to reduce recombination of the excitons.

[0094] In some embodiments, one or more of the absorber domain, the acceptor domain and the extractor domain may be patterned, similar to interface 530 as described above. The optoelectronic device disclosed herein may comprise multiple absorber domains, multiple acceptor domains and multiple extractor domains, where one or more of the multiple absorber domains, multiple acceptor domains and multiple extractor domains may be patterned, similar to interface 530 as described above.

[0095] In some embodiments, the absorber domain (more specifically, the absorber material) may span one or more voids of the acceptor domain. “Void” in the context of the present invention may refer to one or more defects in the acceptor domain or missing parts of the acceptor domain (e.g., a defect resulting from the fabrication process). These voids may be relatively large and some voids may pass through the width of the acceptor domain (e.g., there may be a path from the absorber domain to the extractor domain via the void). In some examples, the absorber domain (or part thereof) may span one or more voids of the acceptor domain. The absorber domain (or part thereof) may span the one or more voids to directly connect the absorber domain to the extractor domain. In other examples, the absorber domain (or part thereof) may span the one or more voids to directly connect the absorber domain to the interface. The absorber domain may passivate the remainder of the optoelectronic device, according to the present disclosure, by spanning one or more voids of the acceptor domain. In other words, as the absorber domain spans one or more voids of the acceptor domain, the extractor domain may become passivated, thereby limiting the recombination of excitons.

[0096] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. An optoelectronic device comprising: an absorber domain of absorber material configured to absorb light to excite the absorber material into an excited absorber energy level; an acceptor domain of acceptor material, the acceptor material comprising an excited acceptor energy level lower than the excited absorber energy level and comprising an intermediate acceptor energy level lower than the excited acceptor energy level; and an extractor domain of charge extraction material, wherein the excited acceptor energy level and the intermediate acceptor energy level are configured to provide for a transition of a first exciton from the excited acceptor energy level to the intermediate acceptor energy level, and the transition generates a second exciton in the intermediate acceptor energy level; and the extractor domain is configured to extract charge provided by the first exciton and the second exciton.

2. The optoelectronic device of claim 1, wherein the optoelectronic device further comprises an interface of interface material associated with the acceptor domain, the interface being configured to facilitate passivation and tunnelling of the first exciton and the second exciton from the acceptor domain to the extractor domain.

3. The optoelectronic device of claim 2, wherein the interface is patterned to facilitate passivation and tunnelling of the first exciton and the second exciton from the acceptor domain at one or more specific locations in the extractor domain.

4. The optoelectronic device of claim 3, wherein the interface is patterned in a tessellating pattern.

5. The optoelectronic device of any one of claims 2 to 4, wherein the interface is formed by atomic layer deposition.

6. The optoelectronic device of any one of claims 2 to 4, wherein the interface material is one of: tin oxide; hafnium oxide; titanium oxide; zinc oxide; aluminium oxide; and amorphous silicon.

7. The optoelectronic device of any one of the preceding claims, wherein the optoelectronic device comprises multiple absorber domains, each of the multiple absorber domains being configured to absorb light of a different wavelength to excite the absorber material into a different excited absorber energy level.

8. The optoelectronic device of claim 7, wherein the multiple absorber domains are configured to form an energy cascade.

9. The optoelectronic device of any one of the preceding claims, wherein the intermediate acceptor energy level is an energy level of a triplet state.

10. The optoelectronic device of claim 9, wherein the excited absorber energy level and the excited acceptor energy level are an energy level of a singlet state.

11. The optoelectronic device of claim 10, wherein the energy level of the singlet state is about twice the energy level of the triplet state.

12. The optoelectronic device of claim 10 or 11, wherein the first exciton undergoes singlet fission to generate the second exciton in the intermediate acceptor energy level.

13. The optoelectronic device of claim 12, wherein the first exciton occurs on a first molecule of the acceptor material and the second exciton occurs on a second molecule of the acceptor material.

14. The optoelectronic device of any one of the preceding claims, wherein the charge extraction material comprises silicon.

15. The optoelectronic device of any one of the preceding claims, wherein the absorber material is one or more of: an organic small molecule; a polymeric dye; a quantum dot; a quantum well superstructure; a quantum well superlattice; and a perovskite material.

16. The optoelectronic device of any one of the preceding claims, wherein the acceptor material is a chromophore.

17. The optoelectronic device of any one of claims 2 to 16, wherein the acceptor domain is disposed between the absorber domain and the extractor domain; and the interface is disposed between the acceptor domain and the extractor domain.

18. The optoelectronic device of any one of the preceding claims, wherein the optoelectronic device is a photovoltaic device.

19. The optoelectronic device of any one of the preceding claims, wherein the absorber domain, the acceptor domain and the extractor domain are layers.

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