Schedule/Budget Overview:

1. Project Title:Multi-Faceted Scientific Strategies Toward Better Solid-State Lighting of Phosphorescent OLEDs Prime Recipient:University of North Texas Principal Investigator:Mohammad A. Omary, Associate Professor of Chemistry Subcontractor Team Member: Bruce E. Gnade, Professor of Electrical Engineering/Vice President for Research, University of Texas, Dallas Agreement Number:DE-FC26-06NT42859 NETL Project Manager:Joel Chaddock

2. Schedule/Budget Overview:

3. Project Objective The objective of this project is to advance phosphorescent OLEDs through: (1) targeted synthesis of emitters designed to exhibit efficient phosphorescence in the solid state. (2) construction and optimizing the performance of monochromatic and white OLEDs on glass and flexible substrates.

4. Design, fabrication, and testing of OLEDs toward satisfaction of the following PL and EL criteria: (1) Phosphorescence as opposed to fluorescence (2) Bright in the solid stateat room temperature (3) Chromaticity suitable for the application (4) Controllable excited-state lifetimes so they are long enough to be phosphorescent, but short enough to prevent triplet saturation (5) Reasonable charge transport properties to allow low drive voltages and high current (6) Amenable to thin film deposition (7) Stability for long operational lifetimes (8) Suitability for conventional and flexible substrates (9) Low manufacturing cost

5. Technical Approach and Work Plan: • Design and synthesize phosphors that satisfy the nine criteria above. The devices developed are designed to achieve the following advantages: • Solid-state packing that causes instead of quenches the emission. This leads to “self-sensitization” instead of “self-quenching” • Single-emitter white OLED devices (SWOLEDs) are targeted such that the white emission comes from one material instead of the common approach that employs combination of RGB emitters. This approach will overcome the common preferential degradation problem • “Fast phosphors” are developed to exhibit phosphorescence recombination lifetimes in the desired microsecond range, which is long enough to be phosphorescence but short enough to prevent triplet-triplet annihilation (a common problem for phosphors) • Synthetic targets include small molecules and macromolecules (polymers and dendrimers), which allows flexibility in the deposition processes via either casting from solution or sublimation of solids • Flexible OLEDs on plastic substrates are targeted, which would greatly reduce the cost of SSL

6. Singlet= Triplet= ; ; Details and background results Why phosphorescence as opposed to fluorescence? Why?  IQEmax = 0.25 (fluorescence) = 1.00 (phosphorescence) Reviews: (a) Yersin, H. Top. Curr. Chem.2004, 241, 1. (b) Sibley, S.; Thompson, M. E.; Burrows, P. E.; Forrest, S. R. Electroluminescence in Molecular Materials. In Optoelectronic Properties of Inorganic Compounds, Roundhill, D. M.; Fackler, J. P., Jr. (Eds.); Plenum: New York, 1999, Ch. 5. • ALL MATERIALS DESCRIBED IN THE APPLICATION ARE PHOSPHORS! (All are metal-organic complexes)

7. Quote from the solicitation: “Of special importance under this topic is research that will increase stability while simultaneously increasing IQE.” (2) Bright in the solid stateat room temperature • Most of our emitters are designed to be brighterand more stable in the solid state • Should exhibit self-sensitization instead of self-quenching! • Indeed, most our phosphors do not even emit in dilute solutions where molecules are separated! •  in contrast to typical emitters, which could have very high F in solution but poor IQE in the solid state.

8. Example 1.EXTERNAL HEAVY-ATOM EFFECT • References:Omary et al. • Inorg. Chem. 2003, 42, 2176-2178. • J. Am. Chem. Soc. 2005, 127, 12166-12167. • Inorg. Chem. 2003, 42, 8612-8614. • Dalton Trans. 2005, 2597–2602. • Inorg. Chem. 2005, 44, 8200-8210. • Inorg. Chem. 2007, 46, 1388-1395.

9. Mechanism of phosphorescence sensitization Omary et al. J. Phys. Chem. C 2007, in press.

10. Example 2. M-M stacking Inorg. Chem. 2006, 45, 6592-6594. J. Am. Chem. Soc. 2005, 127, 7489-7501. J. Am. Chem. Soc. 2003, 125, 12072-12073. (highlighted in “Heart Cut”) Inorg. Chem. 2005, 44, 8200-8210.

11. 3.78 Å 4.33 Å 4.04 Å 4.04 Å 4.04 Å 3.46 4.33 Å 3.78 Å Ground-state crystal structure Phosphorescent-state crystal structure Omary; Coppens et al.Phys. Rev. Lett. 2005, 94, 193003.

12. Chromaticity suitable for the application *: NTSC (x,y) color coordinates: R(0.67,0.33);G(0.21,0.71);B(0.14,0.08); W (0.3104, 0.3191)

13. HEAVY-ATOM EFFECT Complexation of [Hg(o-C6F4)]3, 1, with aromatic hydrocarbons…RGB bright phosphorescent emissions for the 1:1 solid adducts

14. PHOTOINDUCED JAHN-TELLER DISTORTION J. Am. Chem. Soc. 2005, 127, 12488-12489.

15. (4) Controllable excited-state lifetimes so they are long enough to be phosphorescent, but short enough to prevent triplet saturation Typical lifetimes by class of molecules Metal content “Fast phosphors”

16. (5) Reasonable charge transport properties to allow low drive voltages and high current • Most our materials exhibit M-M and M-p stacking, factors that help charge transport… (6) Amenable to thin film deposition • All our small-molecule emitters are neutral by design; we demonstrated that they can be sublimed. • We also make polymer and dendrimer analogues, which can be spin-coated from solution….

17. (7) Stability for long operational lifetimes We’re studying mostly d10 metal-organic phsophors: - Noble gas-like configuration renders superior stability! • Kills other birds in the same stone; quote from application: “Many OLEDs emitters utilized today are based on phosphorescent complexes with partially filled d- or f-shells and emit as monomers. Thus, they exhibit detrimental low-energy d-d or f-f transitions and are prone to self-quenching while our d10 compounds suffer neither!”

18. (8) Suitability for conventional and flexible substrates(9) Low manufacturing cost Quote from application: “While it is impossible to estimate the lamp cost based on research lab results, our emphasis is on using inexpensive materials and processes, so that large scale manufacturing is compatible with low lamp cost. For instance, if our devices require the use of thin, flexible glass as a substrate that has a material cost of $20 ft2, we will never meet the lamp cost goals.”  We have to make OLEDs on plastic Plastic OLEDs; We also make woven displays Table D.1 Commercially Available White-Light LED System Efficacy Estimates

19. Progress-to-Date: The progress made thus far can be summarized as follows in two project tasks: A. Screening of Phosphors: I. Emitters with extended excitation wavelength range. II. Single white-light emitters. B. Monochromatic and White OLED Device Fabrication and Testing: I. White OLEDs Based on Hosts with No Triplet Dopants. II. OLEDs Based on Eu Complexes. III. Single-layer Green OLEDs Based on Iridium Complexes as Dopants. IV. Self-sensitization in OLEDs Based on Pt Complexes.

20. A. Screening of Phosphors: • I. Emitters with extended excitation wavelength range.

22. II. Single white light emitters. Strategy 1. (based on the heavy-atom effect) Burkhart, Dawood. Macromolecules, 1986, 19, 447-452. • Extended excimer phosphorescence observed at RT! • BLUE, ORANGE, and WHITE light-emitting thin films

23. II. Single white light emitters. Strategy 2. (based on an antenna effect synchronized from both organic & inorganic chromophores)

25. II. Single white light emitters. Strategy 3. (based on supramolecular stacking)

26. II. Single white light emitters. Strategy 4. (based on photoinduced Jahn-Teller effect in macromolecular starburst dendrimers) • The broad unstructured emission with a large Stokes’ shift indicates a metal-centered emission with a severely-distorted excited state, consistent with the hypothesis below. • Not too far from white! • Other variations (2nd generation, different dendrimer core, #/position of substituents) are in progress

27. Progress-to-Date: The progress made thus far can be summarized as follows in two project tasks: A. Screening of Phosphors: I. Emitters with extended excitation wavelength range. II. Single white-light emitters. B. Monochromatic and White OLED Device Fabrication and Testing: I. White OLEDs Based on Hosts with No Triplet Dopants. II. OLEDs Based on Eu Complexes. III. Single-layer Green OLEDs Based on Iridium Complexes as Dopants. IV. Self-sensitization in OLEDs Based on Pt Complexes. So far we focused mostly on single-layer OLEDs cast from solution to screen a wide variety of material types

28. B. Monochromatic and White OLED Device Fabrication and Testing: • I. White OLEDs Based on Hosts with No Triplet Dopants. ITO/PEDOT-PSS/PVK:PBD/Ca:Al Now we’re trying to add a hole-blocking layer we designed (HOMO ~ 8 V!!) to further improve the efficiency Exciplex Electroplex

29. II. Red OLEDs Based on Eu Complexes. Typical sensitizer (lexc<400 nm) Inefficient energy transfer; host emission dominates Novel sensitizer (lexc up to 480 nm) Efficient energy transfer; desired dopant emission dominates

30. III. Single-layer Green OLEDs Based on Iridium Complexes as Dopants.

31. Data from this set of devices (reproducible): • luminance efficiency = 12.9 Cd/A at 5.5 mA/cm2, peak power efficiency = 4.65 lumens/Watt • quite high for a single-layer device. e.g., c/p: Tang et al.; J. Appl. Phys. 2002, 92, 156 (arguably best single-layer device for Ir(ppy3): 8.7 Cd/A at 20 mA/cm2)

32. IV. Self-sensitization in OLEDs Based on Pt Complexes. • Need very high solubility in order to attempt to provide proof-of-concept evidence in PLEDs.

33. Higher Pt doping levels led to red-shifted emissions (approaching the neat powder PL spectra), lower driving voltages, and higher current densities. The brightness increased with doping up to 40% while higher doping levels lead to offsetting the self-sensitization effect probably by non-radiative recombination processes. The selection of the Pt complex here was based merely on solubility while ongoing work is focused on expanding this novel concept to brighter phosphors currently being synthesized.

34. On Deck: Other self-sensitizing materials…Conducting phosphors! PL data: Among the brightest phosphors we ever encountered

35. Structural data: Electrical data: Current densities as high as ~ 1 A/cm2!! This value is several orders of magnitude higher than typical current densities for OLEDs. The material behaves as a good diode even when doped in a polymer matrix because the high conductivity suggests that the Au-Au interactions between adjacent trimers seen in the single crystal structure of the material also persist upon doping in the PVK-PBD matrix. The high conductivity should allow us to achieve sufficient current density at lower voltage, consequently providing higher power efficiency, once we improve the energy transfer to the dopant species.

36. Technical Barriers/Problems: None. Milestones/Deliverables:

37. Project Team/Capabilities: The UNT team is headed by PI Omary and the UTD team is led by Professor Gnade. Both groups have proven track records in their respective areas of research that include synthetic chemistry, spectral characterization, and device fabrication and testing. This program is a great opportunity for the two groups to combine their expertise to solve a common problem. The skill sets and infrastructure of the two groups are very complementary, and the close physical proximity of the two universities in the Dallas area makes the collaboration very easy. The two teams hold a general project meeting every two weeks to discuss the results obtained and make plans until the next meeting. All team members regularly exchange data and often exchange visits in the two sites.