Method of formation of multi-component organic layer for an organic optoelectronic device

Abstract

The present invention relates to a method of formation of a multi-component organic layer (322) of an optoelectronic device The method comprises a layer-by-layer sequential structure by deposition of each component of a multi-component organic layer (326) on a pre-defined source substrate (304). Component may comprise host materials, dopant materials, and cohost materials having substantially different sublimation properties. The deposition may be carried out in a vacuum condition. The method further comprises raising a temperature of the pre-defined source substrate (304) over sublimation temperature of the one or more source organic materials (310) by using the optical irradiation sources (320, 314) for rapid pattern and transfer of the one or more source organic thin film (326) as per a pre-defined pattern on a pre-defined product substrate (318) under vacuum conditions, for obtaining a multi-component organic layer (322) of an electronic device.

Description

[0001] METHOD OF FORMATION OF MULTI-COMPONENT ORGANIC LAYER FOR AN ORGANIC OPTOELECTRONIC DEVICE

[0002] FIELD OF INVENTION

[0003] The present invention relates to fabrication of organic optoelectronic devices. More specifically, the present invention relates to the formation of a multi-component functional organic thin film layer for fabrication of organic optoelectronic devices.

[0004] BACKGROUND

[0005] Organic electronic devices, such as Organic Light-Emitting Diodes (OLEDs) are widely used in mobiles, television sets and computer monitor displays now a days. Organic materials used to make such organic electronic devices are synthesized and purified to device grade level, so it costs expensive. Organic electronic devices are made of several layers of organic materials stacked between electrodes. Fig. 1 illustrates a layered arrangement of an organic electronic device, in accordance with prior art. In organic materials, multiple layers such as a Hole Injection Layer (HIL) 102, a Hole Transport Layer (HTL) 104, an Emissive Layer (EML) 106, an Electron Transport Layer (ETL) 108, and an Electron Injection Layer (EIL) 110 may be stacked between an anode 112 and a cathode 114. The anode 112 is placed over a transparent glass substrate 116.

[0006] Conventionally, organic electronic devices are fabricated using a Vacuum Thermal Evaporation (VTE) technique. Fig. 2(a) illustrates a typical VTE apparatus 200 equipped with a source shutter 202 for fabricating organic electronic devices, in accordance with prior art. The VTE apparatus 200 includes a vacuum chamber 204 for depositing a thin film of an organic material 206 on a substrate 208. The deposition is made by heating the organic material 206 which is loaded in a crucible 210, placed below the substrate 208 inside the vacuum chamber 204. Evaporated material is deposited on the substrate 208. VTE technique requires a clean vacuum chamber 204 maintained at high vacuum. The shutter 202 is provided on the vacuum chamber 204 below the substrate 208 in order to avoid the cross contamination between adjacent sources during the organic material 206. A Quartz Crystal Monitor (QCM) 212 is placed near the source substrate in order to accurately measure the thickness of the organic material deposition. In another conventional approach, a VTE apparatus 210, as illustrated in Fig. 2(b), utilizes a shadow mask 212 for depositing an organic material 214 over a substrate 216. The shadow mask 212 has apertures 218 as per a pre-defined pattern for deposition of the organic material 214 which is loaded in a crucible 220. In another conventional approach, a VTE apparatus 210 utilizes a Fine Metal Mask (FMM) for depositing an organic material over a substrate.

[0007] Even though the VTE technique is very well established, the rate of deposition in the VTE process is completely dependent on the thickness of the thin film which is to be deposited. There are some real time limitations involved with the technique which includes a long waiting time required for evaporation of all organic materials, as the organic materials are required to be mixed upon evaporation at a particular rate before deposition.

[0008] In order to deposit an emissive layer containing a mixture of a host material, co-host material and a dopant material, co-evaporation of the materials is used. For co-evaporation of the materials, the rate of evaporation is required to be controlled accurately for achieving the required ratio of the components in the mixture during the emissive layer deposition. However, controlling rate of evaporation and maintaining the ratios of materials in the mixture is critical in the VTE technique. Due to such difficulties, the process time for the deposition may increase leading to cross-contamination of materials and shorter lifetime of the fabricating devices.

[0009] Moreover, VTE is a finite metal mask (FMM) based technique where organic materials are deposited through the mask after precise alignment with the source substrate. During the evaporation, organic materials get deposited on walls of a vacuum chamber which results in poor material utilization. In addition, during evaporation, vacuum chamber is fully covered and organic materials may get deposited on the source substrate surface which leads to cross-contamination between the organic materials. Cross-contamination is a major cause of shorter lifetime of organic electronic devices.

[0010] Thus, a method of fabrication of layer of an organic optoelectronic device is required that enhances material utilization, reduces process time, and improved device lifetime compared to conventional approaches. OBJECTS OF THE INVENTION

[0011] A general objective of the present invention is to provide a method for formation of multicomponent functional organic thin film layer for fabrication of an organic optoelectronic device.

[0012] Another objective of the present invention is to employ a rapid sublimation transfer process for forming a uniform and homogenous mixture of multicomponent organic thin film layer by heating using an optical irradiation source.

[0013] Yet another objective of the present invention is to achieve a maskless organic thin film transfer process with high precision of features.

[0014] Still another objective of the present invention is to form a uniform and homogenous mixture of multicomponent organic thin film by a layer-by-layer sequential structure where the sublimation properties of the organic materials are substantially dissimilar.

[0015] SUMMARY OF THE INVENTION

[0016] The summary is provided to introduce aspects related to a method of formation of an organic thin film layer of an optoelectronic device, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0017] In one embodiment, a method for formation of a multi-component organic layer of an optoelectronic device is described. The method may comprise forming a layer-by-layer sequential structure by deposition of each of one or more organic components of the multicomponent organic layer on a pre-defined source substrate. The deposition may be made under high vacuum conditions. Sublimation properties of each organic component of the multi-component functional organic layer may be substantially dissimilar with each other. The pre-defined source substrate may be heated by a second optical irradiation source by exposing the pre-defined source substrate to sufficient optical irradiation, for raising temperature of the pre-defined source substrate above sublimation temperature of the one or more organic components. The layer-by-layer sequential structure may be rapidly transferred to a pre-defined product substrate under vacuum conditions, for obtaining the multi-component organic layer of the optoelectronic device. The multi-component organic layer formed on the pre-defined product substrate may have a substantially similar thickness from centre of the pre-defined product substrate to individual edges and may have a substantially similar proportion of each organic component present in initially formed layer- by-layer sequential structure on the pre-defined source substrate.

[0018] In another aspect, the multi-component functional organic layer may include a combination of hosts, dopants, cohosts, and any other functional organic material components.

[0019] In another aspect, the pre-defined source substrate and the pre-defined product substrate may be made of a transparent material.

[0020] In another aspect, each of the organic components may be selected from a group consisting of fluorescent, phosphorescent, and thermally activated delayed fluorescence emissive materials.

[0021] In another aspect, area-wise features on regions of the pre-defined source substrate or the pre-defined product substrate may result in a pre-defined pattern, and the area-wise features may include dimension and shape of the regions.

[0022] In another aspect, the multi-component organic layer of the optoelectronic device may be one or more of an Organic Solar cell, an Organic Transistor, an Organic Photodetector, and an Organic Light Emitting Diode (OLED).

[0023] In another aspect, the pre-defined source substrate may include a source principal surface having a plurality of optically reflecting regions and a plurality of optically absorbing regions, and the each of the optically reflecting regions may be surrounded by at least one of the plurality of optically absorbing regions.

[0024] In another aspect, the multi-component organic layer may be one of an Emission layer (EML), a Hole Transport Layer (HTL), a Hole Blocking Layer (HBL), an Electron Transport Layer (ETL), an Electron Injection Layer (EIL), a Hole Injection Layer (HIL) or an Electron Blocking Layer (EBL).

[0025] In another aspect, the pre-defined product substrate may comprise of a pre-defined pattern resulting in a plurality of destination regions corresponding to location of the plurality of optically reflecting source regions present on the pre-defined source substrate.

[0026] In another aspect, sequential arrangement of layers in the layer-by-layer structure formed on the pre-defined source substrate may depend on the dissimilar sublimation properties of the one or more organic components of the multi-component organic layer.

[0027] In another aspect, simultaneous transfer of the layers to the pre-defined product substrate may be performed by controlling energy density of the second optical irradiation source incident on the pre-defined source substrate.

[0028] In another aspect, the multi-component organic layer on the pre-defined product substrate prepared by Close Space Sublimation may exhibit substantially similar photoluminescence properties compared to equivalent functional organic layer prepared by co -evaporation of the one or more organic component of the multi-component organic layer using a vacuum thermal evaporation technique.

[0029] In another aspect, the pre-defined source substrate may be patterned in a first vacuum chamber by selective removal of a film from the optically absorbing regions using a first optical irradiation source resulting in the film remaining only over optically reflective regions.

[0030] In another aspect, a space between the pre-defined source substrate and the pre-defined product substrate during exposure to the second optical irradiation source may be less than 1 mm.

[0031] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention which are used to describe the principles of the present invention. The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this invention are not necessarily to the same embodiment, and they mean at least one. In the drawings:

[0033] Fig. 1 illustrates a layered arrangement of an organic optoelectronic device, in accordance with prior art;

[0034] Fig. 2(a) illustrates an apparatus for Vacuum Thermal Evaporation (VTE) process equipped with a shutter, in accordance with prior art;

[0035] Fig. 2(b) illustrates an apparatus for VTE process equipped with a shadow mask, in accordance with prior art;

[0036] Fig. 3 illustrates a process flow diagram for formation of an organic layer of an optoelectronic device, in accordance with an embodiment of the present invention;

[0037] Fig. 4 illustrates stages of processing by an apparatus for fabrication of RGB pixels for an OLED display by rapid sublimation process, in accordance with an embodiment of the present invention;

[0038] Fig. 5 illustrates a table containing sublimation temperatures of various organic material components in the emissive layer of red, green and blue colours, in accordance with an embodiment of the present invention; and

[0039] Fig. 6 illustrates comparative Photoluminescence (PL) results of a blue fluorescent emissive layer deposited through a layer-by-layer sequence and as a co-evaporated mixture by using a VTE technique and transferred using the said rapid process, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0041] The present invention relates to a method for formation of a multi-component organic layer of an optoelectronic device. The present invention utilises a process of closed space sublimation for fabrication of a thin film organic layer of the electronic device. The prescribed method is a rapid process where the thin film layer of required thickness is predeposited on to a source substrate using a Vacuum Thermal Evaporation (VTE) technique through a layer-by-layer sequential structure of each of components of the multi-component organic layer, where sublimation properties of constituting organic components are substantially dissimilar. An optical irradiation source heats an entire source substrate rapidly and evaporates the organic thin film in order to transfer to a product substrate. Rate of organic thin film layer transfer is much faster as compared to a conventional VTE process. Another interesting phenomenon is that multi-component organic thin film which is deposited as a layer-by-layer structure is capable of producing a uniform and homogenous mixture during rapid transfer on to the product substrate. The prescribed method is capable of transferring an organic thin film on to the product substrate by incorporating a prior patterning step by heating using an optical irradiation source. Thus, the method is considered as a maskless process which contains two steps where a first step is the patterning step and a second step is transfer step of the organic material onto the product substrate.

[0042] Fig. 3 illustrates a process flow 300 for formation of a multi-component organic layer of an optoelectronic device by using the steps of patterning and transfer by rapid sublimation technique, in accordance with an embodiment of the present invention. For formation of the multi-component organic layer, a chamber 302 may be maintained at vacuum condition for depositing on the source substrate 304. In an implementation, the source substrate 304 may be a substantially optically transparent material, such as glass. The source substrate 304 may comprise a plurality of optically reflecting regions 306 and a plurality of optically absorbing regions 308 in a pre-defined arrangement on a surface of the source substrate 304. The plurality of optically reflecting regions 306 may have low light absorbing properties while the plurality of optically absorbing regions 308 may have high light absorbing properties. The plurality of optically reflecting regions 306 and the plurality of optically absorbing regions 308 may be present in a pre-defined arrangement in accordance with a pattern for deposition of an organic thin film 326. The plurality of optically reflecting regions 306 and the plurality of optically absorbing regions 308 may be of variable dimensions and shapes.

[0043] The source organic material 310 may be an optically emissive material like a host material, a co-host material, or a dopant material. The source organic materials 310 may be selected from a group consisting of fluorescent, phosphorescent, and thermally activated delayed fluorescence emissive materials. The source organic material 310 may have substantially dissimilar sublimation properties. The host material and the co-host material may be a carrier for adherence of the dopant material on a substrate. In one implementation, the dopant material may be a light emitting material. The light emitting material may generate illuminance corresponding to primary colours including red, green, and blue or a combination thereof.

[0044] The individual source organic material 310 may be deposited over the source substrate 304 by VTE process to form a layer-by-layer thin film 326. The source organic thin film 326 may cover both the plurality of optically reflecting regions 306 and the plurality of optically absorbing regions 308. In one implementation, the deposition may be performed using VTE technique in the first chamber 302. In one implementation, sequence of deposition of organic materials 310 in the layer-by-layer structure on the pre-defined source substrate 304 can be of any order.

[0045] In one implementation, the deposition of the source organic thin film 326 may be carried out sequentially in a layer-by-layer fashion, to form a multi-layer structure of the various source organic materials 310 on the source substrate 304. The multi-layer structure may be uniformly formed over centre and edges of the pre-defined product substrate 318. The multilayer structure of each of one or more of the host materials, the co-host material, and the dopant material may be made at a pre-defined thickness. For an example, to constitute an emission layer of an Organic Light Emitting Diode (OLED) of thickness 20 nm, a host material of 19 nm thickness may be deposited and then remaining 1 nm of dopant material may be deposited on top of the host material, thereby creating layer-by-layer thin-film structure. In another implementation, the host material, the co-host material, and the dopant material may be mixed together before deposition.

[0046] In the first step, in order to form a pre-defined pattern on the source substrate 304, a capture substrate 312 may be aligned below the source substrate 304 in a first high vacuum chamber 324. The capture substrate 312 may be used to recover the source organic material 310 from the source substrate 304. Distance between the source substrate 304 and the capture substrate 312 may be minimized to prevent spreading of the source organic material 310. In an implementation, the distance between the source substrate 304 and the capture substrate 312 may be maintained to be less than 4mm for the patterning step of an organic thin film. A first optical irradiation source 314 may be illuminated over an entire substrate area of the source substrate 304 for selective removal of the source organic thin film 326 from the plurality of optically absorbing regions 308 for transferring the layer-by-layer structure of the source thin film 326 to the capture substrate 312. Energy density of the first optical irradiation source 314 may be controlled to simultaneously sublime each layer of the layer- by-layer structure on the capture substrate 312. The source substrate 304 may retain the source organic thin film 326 over the plurality of optically reflecting regions 306, thereby obtaining a pre-defined pattern over the source substrate 304.

[0047] In the second step, a second chamber 316 maintained at a low pressure or vacuum condition, the source substrate 304 with the pre-defined pattern may be aligned in parallel with a product substrate 318 such that the patterning is overlapped with a destination region on the product substrate 318. The destination region may be formed on a product principal surface of the product substrate 318 by patterning any metal oxide layer that may as an anode region. In case of fabrication of an optoelectronic device, the organic layers such as hole injection layer and hole transport layer is deposited on the product principal surface using a shadow mask using a conventional VTE process steps. After alignment, the source substrate 304 and the product substrate 318 may be placed over each other in a sample holder. A distance between the source substrate 304 and the product substrate 318 may be minimized to allow precise transfer of the source organic thin film 326 from the source substrate 304 onto the destination region of the product substrate 318. For an example, the distance between the source substrate 304 and the product substrate 318 may be maintained to be less than 1 mm.

[0048] To transfer the source organic thin film 326 from the source substrate 304 onto the destination region of the product substrate 318, temperature may be raised at a location of optically reflecting regions in the plurality of optically absorbing regions 308 onto the destination regions. The temperature may be raised using a second optical irradiation source 320. The second optical irradiation source 320 may be moved over entire substrate area of the source substrate 304, at a fast pace, for complete removal of the source organic thin film 326 from the plurality of optically reflecting regions 306. Raising the temperature above a sublimation temperature of the source organic thin film 326 may be achieved by simultaneous rapid sublimation of the source organic thin film 326 in a multi-layer structure for the complete transfer of the organic thin film to the product substrate. Each layer of the multi-layer structure is uniform and homogeneous in molecular composition. The uniform means that the multi-component functional organic layer formed on the product substrate 318 may have a substantially similar thickness from the centre of the product substrate 318 to the individual edges. The homogeneous means that the multi-layer formed on the product substrate 318 may have a substantially similar proportion of all the individual organic components present in the initially formed multi-layer structure on the source substrate 304.

[0049] The first optical irradiation source 314 and the second optical irradiation source 320 may be one of an incandescence lamp, a photoluminescence lamp, a photonic light lamp, and a Light Amplification by Stimulated Emission of Radiation (LASER). In another implementation, the first optical irradiation source 314 and the second optical irradiation source 320 may include one or more optical irradiation heads to cover entire area of the pre-defined source substrate 304. Energy density of first optical irradiation source 314 and the second optical irradiation source 320 required to remove the source organic thin film 326 may vary as less energy may be required for patterning from the optically absorbing regions 306 when compared to the transfer step from the optically reflecting regions 308. The energy density of the second optical irradiation source 320 incident on the source substrate 304 may be controlled in such a way that each individual layer of the multi-layer structure gets transferred to the product substrate 318 simultaneously. Energy density of the first optical irradiation source 314 and the second optical irradiation source 320 may be controlled by suitable process parameters. The source organic thin film 326 having layer-by-layer structure may be transferred over the product substrate 318 by closed spaced sublimation process. Rapid rise in temperature may cause simultaneous sublimation of all the organic constituents having dissimilar sublimation characteristics of multilayer films 326 which result in formation of a homogenous multicomponent organic film 322 suitable for an optoelectronic device. The optical characteristics of the said homogeneous multicomponent organic films 322 have similar light emission properties as well as Photoluminescence characteristics compared to the film when deposited through co-evaporation of similar organic materials 310 through VTE process. The organic thin film 326 deposited on the predefined source substrate 304 gets 100% transfer to the pre-defined product substrate 318 and the resultant transferred said organic film 322 is a homogenous mixture of all the organic components 310 present in the multi-layer on the predefined source substrate 304. The said organic film 326 have uniform thickness from centre to edges of the pre-defined product substrate 318.

[0050] Further, the source substrate 304 may be checked after the transfer process for any residue of the one or more organic thin film 326 on the plurality of optically absorbing regions 308 and the plurality of the optically reflecting regions 306. If the source substrate contains any organic residue, the residue may be removed by heating the source substrate using the second optical irradiation source 320 over the source substrate 304.

[0051] In one implementation, an optical irradiation source may be selected in such a way that it is capable of ensuring precise transfer of one or more organic thin film 326 present in source substrate 304 to the predefined destination regions on the product substrate. After the complete transfer of the organic material from the source substrate which is one of the organic layers 322 of an optoelectronic device may be checked visually for transfer characteristics and analysed further for physical properties. The transfer characteristics may be validated using PL measurements of the organic layers 322 present on product substrate 318. The thin film 322 characteristics on the pre-defined product substrate 318 may be compared by the wavelength of excitation and other optoelectronic parameters with the thin film 326 formed through the co-evaporation of the organic components by a conventional VTE process.

[0052] Fig. 4 illustrates stages of processing by an apparatus for fabrication of RGB pixels for an OLED display by rapid sublimation process, in accordance with the embodiment of the present invention. The apparatus contains multiple vacuum chambers for the deposition of the organic layer, patterning of the organic layer and transfer of the organic layer. The deposition of the organic layer may be performed through multiple fabrication stages, such as fabrication stage 402-412. At the fabrication stage 402, a predefined patterned source substrate 304 is provided. The predefined patterned source substrate 304 does not contain one or more organic materials. The predefined patterned source substrate 304, the optically reflecting regions 306 are surrounded by the optically absorbing regions 308. Further, Fig. 4 shows the optically reflecting regions 306 as source regions for the red emissive layer for the optoelectronic device fabrication. Next, the predefined patterned source substrate 304 is moved to the fabrication stage 404 where the multi-component organic materials 310 are deposited as a layer-by-layer structure using the conventional VTE process. Following the deposition of the multi-component organic materials in the fabrication stage 404, the predefined patterned source substrate 304 having one or more organic materials are moved to the fabrication stage 406 in a high vacuum chamber 406, where the organic materials are selectively removed from the optically absorbing regions 308 on to a capture substrate using an optical irradiation source. This allows raising the temperature of the organic materials 310 above the sublimation temperature for efficient selective removal from the optically absorbing regions 308. At the fabrication stage 406, the patterned source substrate 304 having organic materials 310 corresponding to a single colour is developed. The predefined patterned source substrate 304 at the fabrication stage 406 is shown to have patterned organic materials 310 of red colour on the optically reflecting regions 306 which will act as one of the functional organic layers for the RGB display device fabrication. Similarly, the predefined patterned source substrate 304 may be repeatedly used for other colours like green and blue organic materials.

[0053] Further, the patterned product substrate 318 with predefined regions of red, green and blue pixels are provided at the fabrication stage 408. Then the patterned product substrate 318 and the patterned source substrate 304 for a single colour is moved to the high vacuum chamber at the fabrication stage 410. The patterned source substrate 304 is placed at top and the patterned product substrate 318 is placed at bottom by maintaining a uniform gap of < 1mm for the precise transfer of organic materials from the source substrate 304 to the product substrate 318 destination regions. Both the source substrate 304 and the product substrate 318 is aligned accurately prior to the transfer of organic materials. The transfer of organic materials from the optically reflecting regions 306 to the product substrate 318 is achieved by heating using an optical irradiation source where the temperature of the organic materials is raised above the sublimation temperature. This results in a complete transfer of organic materials from the source reflecting regions to the product destination regions. Afterwards, a blank predefined source substrate 304 is moved back to the fabrication stage 402 and the product substrate 318 with the patterned product substrate with the organic material of a specific colour is moved to the fabrication stage 412. In order to redeposit organic materials of second colour on the product substrate 318 which is already having the first colour organic material patterns, the above-mentioned process steps are repeated for forming RGB pixels in display fabrication.

[0054] Fig. 5 illustrates a table containing sublimation temperatures of various organic material components in the emissive layer of red, green and blue colours, in accordance with an embodiment of the present invention. The red emissive layer containing host, cohost, and dopant with their respective sublimation temperatures of 200°C, 160°C, and 225°C. The green emissive layer containing host, cohost and dopant with their respective sublimation temperatures of 200°C, 170°C, and 155°C. The blue emissive layer containing host and dopant with their respective sublimation temperatures of 185°C and 140°C. Depositing the red, green and blue emissive materials in a layer-by-layer structure through a conventional VTE process on the source substrate 304 and transferring it to the product substrate 318 by using an optical irradiation source 320, it is found that the ratio of the individual component organic materials in the multi- layer structure remains same after the transfer when compared to the ratio of the individual components in the thin film mixture by co- evaporation, after the transfer for each colour. In accordance to the embodiment of the present invention, it is very well understood that the organic components of dissimilar sublimation temperatures in a mixture which is deposited as a layer-by-layer structure or a co-evaporation by VTE process, the light emission property remains the same and hence the device characteristics are identical to each deposition structure.

[0055] Fig. 6 illustrates comparative Photoluminescence (PL) measurements of a blue fluorescent emissive layer formed using layer by layer deposition and as a mixture deposition using conventional VTE technique, in accordance with an embodiment of the present invention. An emissive layer of thickness 20 nm of organic material having blue luminance was prepared. The emissive layer was prepared using layer by layer deposition of a host material and a dopant material. A deposition of the host material of 19 nm thickness was made over a source substrate 304. Over the deposition of the host material, the dopant material of Inm thickness was deposited by VTE process. A comparative analysis of the emissive layer prepared using layer by layer deposition was performed with an emissive layer prepared as a mixture of the host material and the dopant material using conventional VTE technique. An emissive layer of thickness 20 nm was prepared by VTE using co-evaporation of mixture of a host material and a dopant material in a ratio of 1:0.05. The source substrate was then exposed to optical illumination for rapid sublimation process and then the product substrate was examined for the transfer characteristics. For the comparative analysis, a plot of normalised intensity of the emissive layer against wavelength was prepared. A PL curve of the emissive layer formed by layer-by-layer deposition after processing in transfer chamber is represented by (i). Another PL curve of the emissive layer formed by mixture deposition after processing in the transfer chamber is represented by (ii). Yet another PL curve of the emissive layer formed by mixture deposition after processing in the VTE chamber is represented by (iii). It was observed that curve (i) has a peak at 458nm, curve (ii) has a peak at 460nm and curve (iii) has a peak at 459nm. In light of above-mentioned observations, it may be concluded that thin-film characteristics of the emissive layer deposited as a layer- by-layer structure is similar to thin-film characteristics of the co-evaporated one by using a conventional VTE technique.

[0056] The above-described method may be utilised to fabricate an organic layer of an organic optoelectronic device including Organic Solar cells, organic transistors, organic photodetectors, and OLEDs. Although, present invention describes fabrication of emissive layer of the optoelectronic device, it must be understood that same method may be followed for fabrication of an emission layer, a Hole Transport Layer (HTL), a Hole Blocking Layer (HBL), an Electron Transport Layer (ETL), an Electron blocking layer, an Electron Injection Layer (EIL), or a Hole Injection Layer (HIL). The organic layer may be of different families including organic thin-films such as fluorescent, phosphorescent, and Thermally Activated Delayed Fluorescence (TADF).

[0057] The present invention provides an efficient method of patterning and transferring the multicomponent organic thin-film structures without any change in their chemical composition. Since, both these process steps of patterning and transferring the multi-component organic thin-film structure, take place under high vacuum environment and hence high purity is ensured by reducing the presence of contaminants, which is an essential for the device fabrication. The material wastage is substantially reduced in this process as the multicomponent organic layer is deposited as a layer-by-layer structure, which can rule out a requirement of controlling the rate of deposition as seen in a co-evaporated mixture thin film. Thus, the transferred films have superior characteristics in comparison to VTE grown thin-films. In addition, the method may significantly reduce processing time, minimize wastage of organic material, reduce overall cost of fabrication, and enhance purity and lifetime of the organic devices.

[0058] In view of the present disclosure, which describes the present invention, all changes, modifications and variations within the meaning and range of equivalency are considered within the scope and spirit of the invention. It is to be understood that the aspects and embodiment of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiment may be combined together to form a further embodiment of the disclosure.

Claims

CLAIMS:

1. A method for formation of a multi-component organic layer (322) of an optoelectronic device, the method comprising: forming a layer-by-layer sequential structure by deposition of each of one or more organic components (310) of a multi-component organic layer (326) on a predefined source substrate (304) under vacuum conditions, wherein sublimation properties of each organic component of the multi-component functional organic layer (326) are substantially dissimilar with each other; heating the pre-defined source substrate (304) by a second optical irradiation source (320) by exposing the pre-defined source substrate (304) to sufficient optical irradiation, for raising temperature of the pre-defined source substrate (304) above sublimation temperature of the one or more organic components; and rapidly transferring the layer-by-layer sequential structure to a pre-defined product substrate (318) under vacuum conditions, for obtaining the multi-component homogeneous organic layer (322) of the optoelectronic device, wherein the multicomponent organic layer (322) formed on the pre-defined product substrate (318) has a substantially similar thickness from centre of the pre-defined product substrate (318) to individual edges and has a substantially similar proportion of each organic component present in initially formed layer-by-layer sequential structure on the pre-defined source substrate (304).

2. The method as claimed in claim 1, wherein the multi-component functional organic layer includes a combination of hosts, dopants, co-hosts, and any other functional organic material components (310)3. The method as claimed in claim 1, wherein the pre-defined source substrate (304) and the pre-defined product substrate (318) are made of a transparent material.

4. The method as claimed in claim 1, wherein each of the organic components is selected from a group consisting of fluorescent, phosphorescent, and thermally activated delayed fluorescence emissive materials.

5. The method as claimed in claim 1, wherein area- wise features on regions of the predefined source substrate (304) or the pre-defined product substrate (318) result in a predefined pattern, and wherein the area- wise features include dimension and shape of the regions.

6. The method as claimed in claim 1, wherein the pre-defined source substrate (304) includes a source principal surface having a plurality of optically reflecting regions (306) and a plurality of optically absorbing regions (308), and wherein the each of the optically reflecting regions (306) is surrounded by at least one of the plurality of optically absorbing regions (308).

7. The method as claimed in claim 6, wherein the pre-defined product substrate (318) comprises of a pre-defined pattern resulting in a plurality of destination regions corresponding to location of the plurality of optically reflecting source regions (306) present on the pre-defined source substrate (304).

8. The method as claimed in claim 1, wherein the multi-component organic layer (322) is one of an Emission layer (EML), a Hole Transport Layer (HTL), a Hole Blocking Layer (HBL), an Electron Transport Layer (ETL), an Electron Injection Layer (EIL), a Hole Injection Layer (HIL) or an Electron Blocking Layer (EBL).

9. The method as claimed in Claim 1, wherein sequential arrangement of layers in the layer-by-layer structure (326) formed on the pre-defined source substrate (304), can be of any order.

10. The method as claimed in claim 1, wherein simultaneous transferring of the layers to the pre-defined product substrate (318) is performed by controlling energy density of the second optical irradiation source (320) incident on the pre-defined source substrate (304).

11. The method as claimed in claim 1, wherein the multi-component organic layer (322) on the pre-defined product substrate (318) exhibits substantially similar photoluminescence properties compared to equivalent functional organic layerprepared by co-evaporation of the one or more organic component of the multicomponent organic layer using a vacuum thermal evaporation technique.

12. The method as claimed in claim 1, wherein the multi-component organic layer (322) of the optoelectronic device is used in one or more of an organic photovoltaic cell, an organic transistor, an organic photodetector, or an Organic Light Emitting Diode (OLED).

13. The method as claimed in claim 6, wherein the pre-defined source substrate (304) is patterned in a patterning chamber (324) by selective removal of a film from the plurality of optically absorbing regions (308) using a first optical irradiation source (314) resulting in the film remaining only over optically reflective regions (306).

14. The method as claimed in claim 1, wherein a space between the pre-defined source substrate (304) and the pre-defined product substrate (318) during exposure to the second optical irradiation source (320) is less than 1 mm.

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