AN ORGANIC COMPOSITION AND METHOD OF PRODUCING AN ELECTRONIC ARTICLE COMPRISING THE ORGANIC COMPOSITION

Field of the invention

The invention relates to an organic composition and in particular, but not exclusively, an organic composition for optical sensors generated by a printing process.

Background of the Invention

An important type of electronic components is photoelectrical sensors which are capable of changing their electrical characteristics based on the incident light on the sensor.

It has been found that some organic materials have intrinsic properties that lend themselves to being used as sensors such as their structural simplicity and efficient detection. For example, European Patent EP 1376244 discloses the use of the organic compound titanyl oxyphtalocyanine (TiOPc) as a photoconductor material in e.g. copy machines and United States Patent US4981767 discloses the use of photoconductive mixed crystals of phthalocyanine compounds as an optical sensor.

However, although such organic materials may have very attractive electrical and optical characteristics making them particularly attractive to sensor applications, it is equally important that practical, low cost manufacturing and operational reliability can be

achieved. For example, the materials should be suitable for cost-effective mass production of devices and preferably be suitable for efficient integration in electronic solutions involving other electronic components.

Conventional manufacturing of organic optical sensors such as those described above involves a number of different manufacturing processes including spin-coating, photo-lithographic reproduction using a plurality of layers and films, ultra-high-vacuum organic molecular- beam deposition etc.

For example, EP1689291 discloses manufacturing of the optical sensor using a manufacturing process wherein a solution is spin-coated on a support.

However, such approaches have a number of disadvantages. For example, material is not used efficiently, as most of the material to be coated is lost during a spin-coating or ultra-high-vacuum organic molecular-beam deposition process. Additionally, these processes require an additional patterning step after the deposition, which adds to the complexity and/or cost of the manufacturing process.

Therefore, such conventional approaches result in complicated processing and manufacturing which is often not compatible with other devices of the system in which the sensor is to be used as these devices may be relying on other manufacturing processes. Additionally, processes like those mentioned above are typically not compatible with reel-to-reel manufacturing.

Hence, an improved organic composition would be advantageous and in particular a composition allowing increased performance, facilitated manufacturing, reduced cost, improved performance, improved photoelectrical characteristics, improved mechanical characteristics, improved reliability and/or improved compatibility with operation or manufacturing of other devices would be advantageous .

Summary of the Invention

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to an aspect of the invention there is provided an organic composition comprising: a charge generation material; a non-polymeric charge transport material being one of a hole transport material and an electron transport material; and a polymeric charge transport material being one of a hole transport material and an electron transport material.

The organic composition may provide improved properties and characteristics. In particular, the composition may provide both advantageous electro (optical) properties together with advantageous physical properties, such as advantageous mechanical and/or bonding/binding properties .

In particular, attractive electro-optical sensor properties can be achieved while providing a composition wherein the use of a polymeric and non-polymeric charge transport material allows improved trade-off between electrical and physical properties of the combined composition .

In particular, the inventors have realized that the composition may provide advantageous properties that can allow the composition to be used in a printing manufacturing process of electronic articles, such as a photo sensor.

The invention may allow a significantly reduced complexity and/or reduced cost of manufacturing electronic articles using the composition. In particular, the composition having advantageous electro-optical properties also has physical properties that allow it to be deposited on a substrate by a single step printing process, such as a silk screen process or a stencil printing process. The composition allows a low cost manufacturing process and may allow an increased compatibility with other electronic components or articles that can be manufactured by a printing process.

The invention may provide a low cost printable sensor material .

The inventors have realized that particularly attractive electro-optical/ photoelectrical properties can be achieved by a composition comprising titanyl oxyphtalocyanine (also known as phthalocyanine titanium oxide) as the charge generation material;

triphenyldiamine as the non-polymeric charge transport material and polyvinylcarbazol as the polymeric charge transport material.

In particular, the inventors have identified that for a composition comprising between 5.5% to 7% of titanyl oxyphtalocyanine; between 30% to 33% of triphenyldiamin; and between 60% to 65% of polyvinylcarbazol has particularly advantages properties. In particular, for such a composition extremely attractive electro-optical properties (and in particular light sensing properties) can be combined with physical properties that provide increased reliability of an electrical article and/or allows a printing manufacturing process to be applied.

According to an aspect of the invention, there is provided a method of producing an electronic article, the method comprising generating a device layer comprising the organic composition described above by depositing the composition on a substrate.

The generation of the device layer may specifically comprise dissolving the organic composition in a solvent to generate a printable ink; and depositing the device layer by printing the printable ink on the substrate.

The invention may allow an efficient, low complexity, low cost and/or improved manufacturing of an electronic article. An improved compatibility with other components can be achieved and especially a common single-step printing process may be used to generate a plurality of printed components including an optical sensor having attractive photoelectrical and physical properties.

The article may specifically comprise an optical sensor

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment (s) described hereinafter.

Brief Description of the Drawings

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 illustrates an example of an optical sensor in accordance with some embodiments of the invention;

FIG. 2 illustrates an example of an absorption spectrum for an optical sensor element of the optical sensor of FIG. 1; and

FIG. 3 illustrates an example of a method of producing an electronic article in accordance with some embodiments of the invention.

Detailed Description of Some Embodiments of the Invention

The following description focuses on embodiments of the invention applicable to an optical sensor for detecting incident light. However, it will be appreciated that the invention is not limited to this application.

FIG. 1 illustrates an example of an optical sensor in accordance with some embodiments of the invention.

In the example of FIG. 1, an optical sensing element 101 comprising an organic composition is deposited on a substrate 103 which may be a flexible or rigid substrate. In the example, the substrate 103 is a Printed Circuit Board (PCB) .

The active optical sensing element 101 is coupled to two conductive elements 105, 107 which provide electrical connections to the optical sensing element 101. In the example, a first conductive element 105 is made from copper which is at least partially overlapped by the active optical sensing element 101 whereas the second conductive element 107 is made from a conductive polymer which specifically can be a PEDOT conductive polymer. In the example, the second conductive element 107 partially overlaps the active optical sensing element 101 thereby providing an electrical connection thereto.

As will be known to the skilled person, PEDOT or Poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) is a polymer mixture of two ionomers. Together the charged macromolecules of the two ionomers form a macromolecular salt which is conductive.

The conductivity of the optical sensing element 101 depends on the amount of incident light and accordingly a voltage can be applied between the conductive elements 205, 207 and the resulting current can be used as an indication of the current amount of incident light and accordingly can be used to detect whether light is

currently falling on the active optical sensing element 101.

The composition of the optical sensing element 101 comprises an organic composition which predominantly consists of three different materials. Indeed, typically, more than at least 95% (by weight) of the optical sensing element 101 consist in these three materials and indeed in the specific example the active optical sensing element 101 substantially consists only in the three materials (e.g. apart from impurities and minor contamination by other materials) .

In the system, the organic composition comprises a charge generation material combined with two transport materials wherein one is a polymer and the other is a non-polymer. This composition provides highly advantageous properties and particularly the charge generation material can be optimized for the desired electro-optical characteristics whereas the use of two different transport materials wherein one is a polymer and the other is a non-polymer allows these properties to be combined with attractive physical and electrical transport properties. In particular, the non-polymer transport material can ensure highly advantageous electrical properties which can be combined with the attractive mechanical properties provided by the polymer transport material.

One particular advantage of using more than one charge transport material is the increase of the mobility of the electrical charges. While a single charge transport material, especially a polymeric charge transport material, has a large number of charge carrier traps that

hinder movement of the charge carriers through the material and thereby degrade the electrical properties of the optical sensing element, the addition of a specific amount of a second charge transport material allows the charge carriers to move over these traps by traveling through transport sites in the second charge transport material. Therefore, the electro-optical properties of the sensing element are markedly improved by using a composition comprising two charge transport materials.

In the example, the charge generation material substantially consists in titanyl oxyphtalocyanine (TiOPc) also known as phtalocyanine titanium oxide. Titanyl oxyphtalocyanine provides particularly advantageous electro-optical performance and can in particular provide a high absorption ratio (resulting in a high sensitivity) in the visual light frequency range which tends to be of particular interest in many applications .

In the specific example, the proportion of mass of titanyl oxyphtalocyanine is in the range from 1% to 10 %. It has been found that particularly advantageous properties are achieved for this range. In particular, this proportion of titanyl oxyphtalocyanine is sufficient to provide the desired electro-optical characteristics for many applications (such as high absorption and sensitivity in the visible light frequency range) yet is sufficiently small for the physical properties to typically be dominated by the remaining components of the composition .

Furthermore, in the example, the non-polymeric charge transport material consists in triphenyldiamin (TPD) . Triphenyldiamin is a low molecular weight hole transport material which provides very attractive electrical properties for efficiently moving the generated charges of the charge generating layer to the electrical connections. In particular, the use of low molecular weight non-polymeric material provides a high hole mobility thereby substantially improving the electrical properties of the sensor. At the same time triphenyldiamin has attractive physical properties for a high mobility material.

It will be appreciate that other non-polymeric materials can be used and in particular that other non-polymeric low molecular weight hole transport materials can be used. In particular, many non-polymeric materials having a molecular weight less than 1000 atomic mass units can provide attractive properties.

In the specific example, the proportion of mass of triphenyldiamin in the composition is in the range from 50% to 70 %. This has been found to provide particularly advantageous properties and in particular ensures very advantageous electrical properties while allowing the physical characteristics of the sensor to be improved by introduction of a sufficient amount of polymeric transfer material and allowing the amount of charge generating material to be sufficient for the provision of sufficiently advantageous electro-optical properties.

The polymeric charge transport material may specifically consist in polyvinylcarbazol . This polymeric charge

transport material provides good electrical properties and in addition allows the physical properties to be substantially improved. In particular, the usage of this second transport layer can allow the mechanical strength, flexibility and reliability of the resulting optical sensor to be substantially improved while maintaining high electrical performance.

Particularly advantageous performance is achieved for a proportion of mass of polyvinylcarbazol in the organic composition in the range from 10% to 50 %. This provides a substantial improvement in physical properties yet maintains very advantageous electrical and electro-optical properties of the sensor.

It will be appreciated that although the present example uses hole transport materials, other embodiments may use electron transport materials for at least one of the non- polymeric charge transport material and the polymeric charge transport material.

In the example, the titanyl oxyphtalocyanine, triphenyldiamin and polyvinylcarbazol constitutes at least 99% of the organic composition of the sensor element 101. Thus, a relatively high purity is used for the sensor element ensuring that the electrical, physical and electro-optical characteristics are predominantly dominated by these three components of the composition.

Particularly attractive electrical, physical and electro- optical properties have been found for a composition wherein the organic composition of comprises between 5.5% to 7% of titanyl oxyphtalocyanine;

between 30% to 33% of triphenyldiamin; and between 60% to 65% of polyvinylcarbazol .

Specifically, the organic composition can comprise substantially 6.25% of Titanyl oxyphtalocyanine; substantially 31.25% of triphenyldiamin; and substantially 62.5% of polyvinylcarbazol.

(The fractions representing the proportion of the total mass of the composition)

Such organic compositions have been found to allow a highly efficient and sensitive sensor operation with desirable electrical and optical properties. For example, FIG. 2 illustrates the absorbance as a function of frequency of a sensor element using such a composition. As illustrated, the peak sensitivity can e.g. be provided in the visual light range e.g. a wavelength of around 350 nm. Indeed, experiments have demonstrated that an optical sensor element using such an organic composition can provide a charge generated current of ca. 10 μA/cm ^? at full illumination. Furthermore, a very high charge current ratio between full light and no light can be achieved with ratios of more than 50 being achievable.

Furthermore, the composition provides very attractive physical properties and in particular allows an active optical sensor element to be generated which has mechanical stability and reliability combined with attractive binding properties.

Specifically, the composition can be dissolved in a suitable solvent thereby generating a solution which can

be used as a printable ink. Thus, the described organic composition can be used in a printing manufacturing process thereby resulting in a low cost, low complexity and efficient manufacturing of electronic articles such as the described optical sensor.

Suitable solvents that provide suitable characteristics both for the generation of the solution/printable ink and for the printing of this include Chlorobenzene, Dichlorobenzene, Tetrahydrofuran, and Dichloromethane .

FIG. 3 illustrates an example of a method of producing or manufacturing an electronic article, such as an optical sensor .

Initially a printable ink is generated using a solvent and subsequently the printable ink is printed on a suitable substrate.

Specifically, the method initiates in step 301 wherein the non-polymeric charge transport material and the polymeric charge transport material are dissolved in a solvent.

This is followed by step 303 wherein the charge generation material is added to the solvent and dispersed therein .

In the specific example, the printable ink is manufactured by first adding the low-molecular weight transport material to the solvent and dissolving it.

Then, the polymeric charge transport material is added to the solution and dissolved. Dissolution of the charge transport materials may be accelerated by using a

mechanical stirrer. The charge generation material is then added to the solution. The charge generation material is then finely dispersed in the solution with the help of a mechanical stirrer, an ultrasonic bath, or a ball mill .

The method then proceeds to generate a device layer (which specifically can be an optical sensor element layer) comprising the organic composition by depositing this printable ink on a substrate.

In the specific example, this process comprises a printing process and step 303 is followed by step 305 wherein the printable ink is printed on a substrate using a suitable printing process such as a stencil or silk screen printing process. The substrate may be a suitable rigid or flexible substrate such as a PCB.

In the example, the printing of the sensor element comprising the composition is performed in a single step together with the printing of other elements or components. Specifically, the printing process step also comprises the printing of at least two electrical contacts to the device layer (i.e. to the sensor element) .

Thus, the described materials and system allows an optical element to be generated by a simple single step and low cost printing process. The materials and the proportion of these in the organic composition used for the optical sensor element combine to provide highly advantageous physical, electrical and optical parameters. In particular, an efficient optical sensor can be

achieved from a composition that has physical properties suitable for use in a printing manufacturing process.

It will be appreciated that the optical sensor can be used for many different applications including for example the gathering of environmental/ structural conditions .

It will be appreciated that references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the

inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate. Furthermore, the order of features in the claims does not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order.