Obviousness

Obviousness Analysis of US Patent 8,723,164 under 35 U.S.C. § 103

This analysis assesses the obviousness of US Patent 8,723,164 (hereinafter "'164 patent") based on the provided prior art. The '164 patent generally claims an electronic device, such as an Organic Light-Emitting Diode (OLED), comprising at least one organic functional layer with a combination of at least three matrix materials having specific Lowest Unoccupied Molecular Orbital (LUMO) and Highest Occupied Molecular Orbital (HOMO) energy level relationships. The invention aims to improve charge carrier transport and balance, thereby increasing device efficiency.

A person having ordinary skill in the art (POSITA) in the field of organic electronic devices, such as OLEDs, at the time of the '164 patent's priority date (May 30, 2008), would have been familiar with the fundamental principles of OLED operation, including charge injection, transport, and recombination, as well as the significance of HOMO and LUMO energy levels for material selection. A POSITA would also recognize the common problem of unbalanced charge carrier transport leading to reduced device efficiency and lifetime.

Independent Claims to be Analyzed:

• Claim 1: Directed to an electronic device with a substrate, electrodes, and an organic functional emission layer doped with an emitter material, wherein the emission layer has at least a first, second, and third matrix material. The claim specifies relative HOMO/LUMO energy levels: the third matrix material has a LUMO lower than the LUMO of the second and first matrix materials, and the second matrix material has a HOMO higher than the HOMO of the first and third matrix materials.
• Claim 13: A method for producing the electronic device of claim 1, comprising simultaneously applying the three matrix materials (e.g., by coevaporation).
• Claim 15: Similar to Claim 1, but further specifies that the first matrix material has a LUMO higher than the LUMO of the second and third matrix materials, and a HOMO lower than the HOMO of the second and third matrix materials.
• Claim 16: Similar to Claim 1, but further specifies that the first matrix material has a charge carrier mobility lower than the charge carrier mobilities of the second and third matrix materials.

Combinations of Prior Art References and Motivation for Combination:

The core inventive concept of the '164 patent lies in the use of three matrix materials in an organic functional layer, particularly an emission layer, with specific energy level alignments to manage charge carrier transport. The first matrix material is typically characterized by a large band gap and low charge carrier mobility, functioning as an electrically inactive diluent.

Combination 1: Tsai et al. (2006) in view of general knowledge in the art (including Miller et al. (1960) and Schwartz et al. (2006))

1. Tsai, Yung-Cheng et al., "Long-lifetime, high-efficiency white organic light-emitting diodes with mixed host composing double emission layers," Applied Physics Letters (2006):

   • Disclosure: This non-patent literature reference explicitly teaches the use of "mixed host" systems in OLEDs to improve carrier injection balance and suppress color shift. It highlights the problem of color change due to a shift in the recombination zone and seeks to confine this zone. The paper states that "adding TBRb in NPB can improve the balance of carrier injection into emitting layer to reach longer operational durability." This demonstrates the concept of using multiple components within a host system to achieve improved charge carrier balance and device stability. While it describes "dual emitting layers" each potentially with mixed hosts, it establishes the motivation for and efficacy of tailoring the host environment with multiple materials to manage charge carriers.
   • Relevance to '164 Patent: Tsai et al. provides the foundational motivation for using mixed hosts to address charge imbalance and improve efficiency/lifetime in OLED emission layers, which is a primary objective of the '164 patent.

2. General Knowledge in the Art (e.g., implicit in Miller et al. (1960) and understood by a POSITA):

   • A POSITA would understand that different organic materials possess varying intrinsic hole and electron transport characteristics, directly related to their HOMO and LUMO energy levels. Specifically, a material with a high HOMO is suitable for hole transport, and a material with a low LUMO is suitable for electron transport.
   • A POSITA would also understand that the concentration of active charge-transporting molecules within a matrix influences their effective charge carrier mobility. Lower concentrations increase the average hopping distance between active molecules, thereby reducing mobility. The '164 patent itself cites Miller, Allen et al., "Impurity Conduction at Low Concentrations," Physical Review (1960), indicating the relevance of concentration to mobility in the field.
   • Schwartz, Gregor et al., "High efficiency white organic light emitting diodes combining fluorescent and phosphorescent emitter systems," Proc. of SPIE (2006), while focusing on emitter systems, generally discusses "reducing energetic and ohmic losses that occur during electron-photon conversion." This broadly points to the ongoing effort to optimize charge transport and energy transfer to improve OLED efficiency, reinforcing the motivation for the work described in Tsai et al.

Motivation for Combination and Obviousness:

A POSITA, motivated by the teachings of Tsai et al. to improve charge carrier balance and device stability in OLEDs using mixed host systems, would naturally seek further methods to precisely control and independently adjust the mobilities of holes and electrons within the emission layer. The problem of unbalanced charge transport was well-recognized.

Starting from a mixed host containing at least two materials (one primarily for hole transport and one primarily for electron transport, or an ambipolar host alongside a selective transport material), a POSITA would recognize that to fine-tune the relative mobilities, simply adjusting the ratio of these two active components might not provide sufficient independent control, or might inadvertently alter other critical properties.

A POSITA, aware of the relationship between concentration and mobility (e.g., as taught by Miller et al., or general knowledge), would be motivated to introduce a third matrix material that is substantially electrically inactive (i.e., having a large band gap, with a high LUMO and low HOMO, such that it does not participate significantly in charge transport itself). This third, inactive material would then serve as a "diluent" or "spacer." By independently varying the concentration of this inactive third material, a POSITA could then adjust the average distances between the molecules of the hole-transporting second matrix material and the electron-transporting third matrix material, thereby independently controlling their effective mobilities within the emission layer.

The specific HOMO/LUMO relationships recited in Claim 1 (third matrix material having the lowest LUMO, second matrix material having the highest HOMO) would be an obvious choice for a POSITA intending to designate one material primarily for electron transport and another for hole transport, respectively. Likewise, the further characteristics of the first matrix material in Claims 15 and 16 (high LUMO and low HOMO to effectively block transport, and low charge carrier mobility) are precisely the properties a POSITA would select for an electrically inactive diluent. The goal of using such a diluent would be to modulate the effective concentrations of the two active transport materials without introducing new, undesirable charge transport pathways.

Regarding Claim 13 (Method Claim):

The method of simultaneously applying multiple matrix materials, such as by coevaporation, was a standard and well-known technique in OLED fabrication for creating mixed layers with precisely controlled concentrations of components. The '164 patent itself describes this in its detailed description (e.g., referring to FIG. 5 and evaporation sources with layer thickness monitors). Therefore, applying three matrix materials simultaneously via evaporation coating to achieve desired concentrations would have been an obvious manufacturing choice for a POSITA seeking to implement a three-matrix-material layer.

Conclusion of Obviousness:

It would have been obvious to a POSITA, at the time of the invention, to combine the teachings of Tsai et al. (2006) regarding the use of mixed host systems for improving charge carrier balance and device performance with the general knowledge in the art (including principles of charge transport and concentration effects as understood by a POSITA, and concepts implicitly referenced in Miller et al. (1960) and broadly related in Schwartz et al. (2006)). A POSITA, motivated to further optimize charge balance and control individual carrier mobilities, would have been led to introduce a third, electrically inactive matrix material with appropriate HOMO/LUMO levels (as described for the first matrix material in the '164 patent). This inactive material would serve as a diluent, allowing for independent adjustment of the concentrations (and thus mobilities) of the primary hole and electron transport materials, thereby achieving the desired adaptable ratio of hole and electron transport and improved efficiency. The specific energy level relationships of the three matrix materials as claimed are the logical outcome of selecting materials for these functionally distinct roles (electron transport, hole transport, and inert diluent). The method of simultaneous application (Claim 13) would also be an obvious manufacturing choice using conventional techniques like coevaporation.