DE102012021174A1 - Organic semiconductor laser with trip-line manager - Google Patents

Abstract

A first device is provided. The device comprises an organic semiconductor laser. The organic semiconductor laser further includes an optical resonator and an organic layer disposed in the optical resonator. The organic layer comprises: an organic host compound; an organic emissive compound capable of fluorescence emission; and an organic dopant compound. The organic dopant compound may also be referred to herein as a "triplet manager". The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound. The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic emissive compound. The singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority and is a continuation-in-part of US Application Serial No. 13 / 283,284, filed October 27, 2011, which is hereby incorporated by reference in its entirety.

DECLARATION OF RIGHTS TO INVENTIONS RESULTING FROM STATE-SUPPORTED RESEARCH OR DEVELOPMENT

The present invention was made with government support under FA9550-10-1-0339 granted by AFOSR ("Air Force Office of Scientific Research"). The present invention was under government support DE-500001013 made by the US Department of Energy's Energy Frontier Center at the University of Southern California. The government has certain rights to the invention.

The claimed invention has been made by, in the name of and / or in association with one or more of the following participants in a joint university and enterprise research agreement: administrators from the University of Michigan, Princeton University, the University of Southern California, and Universal Display Corporation. The Agreement was valid on and before the date on which the claimed invention was made, and the claimed invention was made as a result of activities undertaken under the Agreement.

The present application is related to U.S. Application Serial No. 12 / 117,926, filed May 27, 2011, which is the priority of US 61 / 396,862 , filed on 3 June 2010, and the US 61 / 398,627 , filed June 29, 2010. These related applications are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to lasers that use organic substances.

GENERAL PRIOR ART

Opto-electronic devices using organic materials are becoming more and more desirable for a variety of reasons. Many of the materials used to make such devices are relatively inexpensive, so that organic optoelectronic devices have the potential for cost advantages over inorganic devices. In addition, because of their inherent properties, such as flexibility, organic materials may be well suited to particular applications, such as the manufacture of a flexible substrate. Examples of organic optoelectronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors.

Various ways of depositing the organic materials used to fabricate organic devices, such as thermal vacuum evaporation, solution processing, organic vapor deposition, and organic vapor jet printing, are known.

SUMMARY OF THE INVENTION

A first device is provided. The device comprises an organic semiconductor laser. The organic semiconductor laser further includes an optical resonator and an organic layer disposed in the optical resonator. The organic layer comprises: an organic host compound; an organic emissive compound capable of emitting fluorescence; and an organic dopant compound. The organic dopant compound may also be referred to herein as a "triplet manager". The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound. The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic emissive compound. The singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound.

According to some embodiments, in the first device described above, the singlet energy of the organic emissive compound is smaller than the singlet energy of the organic host compound.

Preferably, the singlet energy of the organic emissive compound is less than the singlet energy of the organic dopant compound.

Preferably, the organic dopant compound does not strongly absorb the fluorescence emission of the organic emissive compound.

In one embodiment, the first device further includes an optical pump optically coupled to the organic layer.

According to an embodiment, the organic semiconductor laser further comprises an anode and a cathode. The organic layer is disposed between the anode and the cathode. A hole transport layer is disposed between the organic layer and the anode. An electron transport layer is disposed between the organic layer and the cathode. The organic dopant compound is present only in the emission layer.

Preferably, the triplet decay time of the dopant compound is shorter than the triplet decay time of the emitting compound.

Preferably, the concentration of the doping compound ranges from 10 to 90% by weight, and the concentration of the emitting compound ranges from 0.5 to 5% by weight.

Preferably, the organic emissive compound is capable of fluorescence emission at room temperature.

Preferably, the doping compound is selected from the group comprising: anthracene, tetracene, rubrene and perylene and their derivatives. More preferably, the doping compound is selected from anthracene, and its derivatives are particularly preferred. More preferably, the doping compound is ADN.

According to some embodiments, the dopant compound is a phosphor. According to some embodiments, the dopant compound is a fluorophore.

According to some embodiments of the first device described above, the organic semiconductor laser may further comprise a feedback structure. According to some embodiments, the feedback structure may include any or some combination of a planar waveguide structure, a distributed feedback structure, a Bragg reflector feedback structure, or a vertical cavity structure (VCSEL) structure.

According to some embodiments of the first device described above, the organic semiconductor laser may further comprise a substrate. The anode of the device may be disposed over the substrate, and at least one mirror is disposed between the substrate and the anode.

According to some embodiments of the above-described first device, the organic semiconductor laser may further comprise a hole injection layer disposed between the anode and the hole transport layer and an electron injection layer disposed between the cathode and the electron transport layer.

The first device may be a consumer product.

A method is provided. An organic semiconductor laser is provided. The organic semiconductor laser further includes an optical resonator and an organic layer disposed in the optical resonator. The organic layer comprises: an organic host compound; an organic emissive compound capable of fluorescence emission; and an organic dopant compound. The organic dopant compound may also be referred to herein as a "triplet manager". The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound. The triplet energy of the organic dopant compound is less than or equal to Triplet energy of the organic emissive compound. The singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound. The organic semiconductor laser is pumped to achieve laser operation.

According to some embodiments of the method described above, the singlet energy of the organic emissive compound is less than the singlet energy of the organic host compound.

In one embodiment, the pumping is optical pumping.

According to one embodiment, the pumping is an electric pump.

When the organic semiconductor laser is pumped, laser operation is achieved for at least 1 microsecond.

According to some embodiments, the organic semiconductor laser is pumped at a power that exceeds the pulse threshold.

According to some embodiments, the organic semiconductor laser is pumped at a power exceeding the continuous wave threshold.

In one embodiment, the organic semiconductor laser is pumped at a power exceeding the continuous wave threshold for at least 1 microsecond, and more preferably at least 100 microseconds.

BRIEF DESCRIPTION OF THE DRAWINGS

1 shows separate channels for singlet (S) and triplet (T) formation and transport into the triplet-managed lasers. Both singlets (circles) are generated on both Alq ₃ and ADN and transferred to DCM2 Förster (continuous arrows). Triplets are generated by intersystem crossing (ISC) or singlet cleavage and are collected by ADN by Dexter transfer (dashed arrows).

2 shows transients (a) of photoluminescence (PL) and (b) laser operation measured at a pump intensity of 1.6 kW / cm ² for various host mixtures. The PL transients are normalized by the peak intensities, and the lasing transients are normalized to 1 for x = 0.10, and 30 ADN mixtures, and to 5 for x = 50 and 70. The adjustments are made by the model, which is summarized as text with parameters in Table 1. Inset: Laser operating spectrum of an OSL with x = 70.

3 shows a simulated singlet threshold population, S _TH (t) with x = 70 (asterisks) and no triplet manager (squares), and S (t) (lines) for the OSL with x = 70. Laser operation occurs when S ≥ S _TH . The dashed lines correspond to lasers that have not exceeded their pulsed singlet threshold population (S _PS ) but their CW threshold (S _CW ). Inset left: Streak camera image of the laser emission for a triplet-managed OSL (x = 70), measured at a pump intensity of 2.4 kW / cm ² , pulse width 18 μs. Insert on the right: Simulated development of the laser operating time with increasing pumping power for a triplet-managed OSL with x = 70.

4 shows: 4 (a) Photoluminescence (PL) spectra of thin-film ADN (squares), Alq ₃ (circles) and DCM2, which are transformed into a mixture of x% ADN / (100-x)% Alq ₃ with x = 0 (asterisks) and 70 (triangles ) are doped. The shaded area corresponds to the location where the DCM2 absorption coefficient is> 4 × 10 ⁴ cm ^-1 , which involves efficient energy transport from both ADN and Alq ₃ . 4 (b) the phosphorescence of Alq ₃ , DCM2 and ADN measured at 14 K, the fits are for a dual peak Gaussian for Alq ₃ and for single peak Gaussian functions for the remainder.

5 shows a test pulse PL spectrum with and without a pump pulse for (a) x = 0; and (b) x = 70 layers. The 200 nm layer was grown on a substrate of SiO ₂ (2 μm) / Si.

6 forms the calculation of an absorption coefficient for x = 0 and 70 from the data in 5 from.

7 shows a streak camera image of a laser emission for a triplet-managed OSL with x = 70, measured at a pump intensity of 2.4 kW / cm ² and a pulse width of 100 μs, integrated over 10 Impulse. It should be noted that the color table uses a logarithmic scale. The laser operating time (characterized by a narrow spectrum) is approximately 55 μs. The wavelength of the laser operation is a little different than the insertion in 3 because these two lasers are not made simultaneously and the thicknesses of their gain media or grating periods may be slightly different.

8 (a) maps EL transients from OLEDs with different concentrations (0.10%, 30%, 50%, 70% bottom to top) of ADN as a triplet manager, which is pumped at 2 A / cm ² using rectangular current pulses , The lines are adjustments to the model. 8 (b) shows a triplet absorption coefficient, α _r , for ALq ₃ and ADN layers doped with 2% DCM2 versus wavelength.

9 maps the ratio of peak-to-peak intensity (ρ on the left axis) as a function of current density for OLEDs with different concentrations of ADN. The corresponding triplet guest populations (N _GT on the right axis) are calculated below.

10 (a) maps the EQE or triplet-managed OLEDs with different concentrations of ADN (x). The filled symbols are from steady state measurements and the empty symbols are from transient measurements. The inset shows the properties of current density to voltage (JV) for OLEDs with x ≤ 50% (almost identical) and x = 70%. 10 (b) maps the triplet (η _r ) and charge (η _c ) induced external quantum efficiency (EQE) attenuation for OLEDs with x = 0 and 50%.

11 shows the different feedback structures used in the current OSL architecture.

DETAILED DESCRIPTION

An organic laser model has been developed that predicts two threshold pump intensities in optically pumped organic semiconductor lasers (OSLs); one for pulsed laser operation, I _PS , and another for continuous wave (CW) laser operation, I _CW . The theory predicts a reduction of the I _CW from 32 kW / cm ² , or well above the damage threshold, to 2.2 kW / cm ² for a laser paired with 4- (dicyanomethylene) -2-methyl-6-julolidyl -9-enyl-4H-pyrane (DCM2) doped tris (8-hydroxyquinoline) aluminum (Alq ₃ ) is used when the triplets can be effectively removed from the emitting guest material. Based on this analysis, it has been demonstrated that the lasing lifetime can be extended to nearly 100 μs, ultimately limited by the degradation of the laser operating medium when a "triplet manager" molecule, 9,10-di (naphtha-2 -yl) anthracene (ADN), is mixed into the gain area of a distributed feedback OSL. The triplet manager facilitates radiative singlet transport while suppressing non-radiative triplet transport to the emitter molecule, thereby reducing triplet-induced losses. Our theory clearly shows that these lasers have entered the CW laser regime.

Optically pumped organic semiconductor lasers (OSLs) with low thresholds and wide spectral tuning ranges have aroused interest since their detection fifteen years ago. However, a major obstacle to the application of OSL has been its limitation to pulsed operation alone with a maximum duration of tens of nanoseconds. This limitation is created by the accumulation of triplet (T) excitons in the gain region generated by intersystem crossing (ISC) from radiating singlets (S). Since the relaxation of T into the ground state is forbidden quantum-mechanically, the T-exciton has a long lifetime (~ ms) compared to S (~ ns), so that the T-population can accumulate over time. The large T-population, coupled with overlapping S-emission and T-absorption, results in singlet and photon losses that ultimately shut off laser operation, thereby preventing continuous wave (CW) operation.

Although triplet losses in liquid dye lasers can be reduced by using quencher molecules having triplet energies smaller than that of the dye, no CW operation was achieved without dye circulation. With OSL, circulation of the gain medium is not possible; however, various efforts have been made to mitigate the triplet losses as much, if not to fix, that the CW operation is achievable. Bornemann et al., Opt. Lett. 31 (11), 1669-1671 (2006) , have used a fast rotating substrate to detect a CW semiconductor dye laser, but the output was not constant. Schols et al., ChemPhys Chem 10 (7), 1071-1076 (2009) , have shown that "scavengers" can be used to de-excite triplets, but no improvement in laser operation has been demonstrated. Rabe et al., Appl. Phys. Lett. 89 (8), 081115 (2006) , and Leahhardt et al., Org. Electron. 12 (8), 1346-1351 (2011) , have demonstrated a polymer OSL pumped by very low duty cycle pulses (<0.1%) to extend the total duration to 400 μs, although this is not a true CW operation.

Here, a "triplet manager" is introduced into the enhancement region along with the guest emitter and host molecules. The manager reduces the triplet population of the emitter, thereby extending laser life. The inset in 1 shows the concept of triplet management. The manager has lower triplet energy and higher singlet energy than the emitter. When either the host or the managerial molecules are excited, the Förster transfer from S-states to the emitter is very efficient. Furthermore, Dexter transfer of triplets causes them to be trapped on the manager because they have lower triplet energy than both the guest and the host. The triplet absorption of the manager shifts from the guest emission, and thus the trapped triplets do not contribute to optical losses or singlet cancellation.

The 200 nm active region of the OSL consists of the manager, 9,10-di (naphtha-2-yl) anthracene (ADN), which is simultaneously deposited in the conventional guest-host amplification medium consisting of 2% by volume. of red emitting 4- (dicyanomethylene) -2-methyl-6-julolidyl-9-enyl-4H-pyran (DCM2) in tris (8-hydroxyquinoline) Al (Alq ₃ ). The S and T energies are determined in each case from the fluorescence at room temperature and the phosphorescence at 14 K, see EPAPS. In this case, ADN has a lower T- (1.69 eV) and a higher S-energy (2.83 eV) than Alq ₃ (T = 1.99 eV and S = 2.38 eV). Further, S = 2.03 eV and T = 1.74 eV for DCM2. This system is therefore energetic 1 match.

The manager concentration at (100-x) vol.% Alq ₃ is x vol.% ADN (x = 0, 10, 30, 50, 70, 100). Mixed layers were deposited by thermal evaporation in high vacuum (10 ^-7 Torr) on quartz, Si and 2 μm thick SiO ₂ on Si substrates to characterize each absorption, photoluminescence (PL) and triplet absorption. The same layers were deposited on lattices 430 nm ± 5 nm apart and 50 nm deep on the SiO ₂ on Si to form distributed feedback (DFB) OSL. The output of a 0.6 W laser diode at a wavelength of λ = 405 nm was focused on a spot of 150 μm × 250 μm in order to optically pump the thin film. The pure layer absorption coefficients of Alq ₃ and ADN were measured to be 4.8 x 10 ⁴ cm ^-1 and 9.1 x 10 ^-4 cm ^-1 at λ = 405 nm, and are believed to contribute to the total absorption of the mixed layer in proportion to their volume. All measurements were taken in an N ₂ environment to minimize stratification.

2 (a) and (b) show the PL and laser operating transients pumped at 1.6 kW / cm ² . In 2 (a) The Alq ₃ host experiences a 55% reduction in PL to its steady state value within 30 μs of the start of pumping. Previous research has shown that this intensity attenuation is due to the singlet cancellation of ST annihilation. Ie. After the onset, the S-density rapidly peaks and then decays due to the annihilation by the slowly increasing T-population. The presence of the long-term steady state PL intensity below its peak suggests saturation of the guest triplet population. By including the ADN manager in the host mix with x = 10 to 70, PL transient cancellation is reduced to 17%. Furthermore, increasing to x> 70 can completely eliminate erasure. Hence, we deduce that triplets are transferred from Alq ₃ to DCM2 while the transfer from ADN to DCM2 is inhibited, in accordance with the triplet energy relationship T (Alq ₃ )> T (DCM2)> T (ADN). It should be noted, however, that morphology degradation occurs at high pumping intensity for x> 50, consistent with the previous observation of the morphological instability of ADN.

In 2 B) For example, a more than 10-fold increase in laser operating time (from about 400 ns to 4.5 μs) is observed as x increases from 0 to 70. Laser operation is not observed for x = 100 due to degradation. The inset shows a typical laser operating spectrum of an OSL with 70% ADN centered at λ = 687.9 nm, with a full-width half-maximum of 0.15 nm, which is limited by the resolution of the spectrometer. The pulsed pump intensity threshold, I _PS (characterized by a sudden spectral narrowing of> 30 nm to <0.5 nm and a marked increase in tilt efficiency) was achieved using a pump pulse of 30 ns (Table 1). Table 1: Parameters for adaptations of PL and laser operating transients and the corresponding measured, pulsed (I _PS ) and calculated CW (I _CW ) laser operating threshold intensities Device (% ADN) I _TH † (kW / cm ² ) k _HG * (10 ¹⁰ / s) k _ISC * (10 ⁷ / s) N ₀ * (10 ¹⁸ / cm ³ ) σ _TT † (10 ^-17 m ² ) σ _stim * (10 ^-16 cm ² ) I _CW (kW / cm ² ) 0 0.93 4.0 3.3 5.0 ± 0.4 4.0 ± 0.3 1.9 32 10 0.75 3.5 2.6 3.9 ± 0.3 3.8 ± 0.3 2.0 19 30 0.72 13 2.3 2.8 ± 0.3 3.6 ± 0.4 2.4 8.8 50 0.45 3.0 × 10 ³ 1.7 1.5 ± 0.2 4.3 ± 0.6 2.1 3.7 70 0.43 5.0 × 10 ⁵ 1.3 0.92 ± 0.08 4.1 ± 0.4 2.3 2.2 † Parameters of Measurement * Parameters of adjustments to the data

wobei S, T_H, T_G, P jeweils die Photonendichten von Gast-Singulett, Wirtsmischung-Triplett (einschließlich sowohl ADN als auch Alq₃), Gast-Triplett und Laserbetriebsmodus sind, t die Zeit ist, η der Anteil der Pumpemission ist, die von der organischen Schicht absorbiert wird, I die Pumpintensität ist, e_p = 3,06 eV die Pumpphotonenenergie ist, d = 200 nm die Dicke des OSL-Verstärkungsmediums ist, k_S = (6,7 ± 0,5) × 10⁸s^–1 die natürliche Abklingrate des Gast-S ist (gemessen an einer 2%igen DCM2:Alq₃-Schicht, die durch 1,5 ns breite N₂-Laserimpulse angeregt wird), k_ISC die Wirts-ISC-Rate ist, k_ST die Gast-S-T-Annihilationsrate ist, γ = σ_stimS die Verstärkung ist, σ_stim der stimulierte Emissionsquerschnitt ist, c die Lichtgeschwindigkeit ist, und n_eff = 1,6 und Γ = 0,69 der effektive Brechungsindex und der optische Einschlussfaktor für den Wellenleiter aus SiO₂ (n = 1,48)/organisch (n = 1,82)/Luft (n = 1) sind.²⁴ Ebenso ist k_HG der Wirt-Gast-Dexter-Transferkoeffizient, L ist der Gast-Wirt-Van der Waals-Radius (~1 nm), N₀ ist die Gast-Triplett-Sättigungspopulation, α_CAV ist der Resonatorverlust ohne Beiträge der Triplett-Absorption, α_TT, und σ_TT ist der Gast-Triplett-Absorptionsquerschnitt, und β ≈ 10^–4 ist der spontane Emissionsfaktor²⁵. Für die PL erhalten wir P = 0, und die Intensität ist proportional zu S. Man geht davon aus, dass die Wirt-Triplett-Population nicht mit S oder P interagiert; dies wird durch Anpassungen an die Daten und über direkte Triplett-Absorptionsmessungen getestet. Nun wird N₀ aus der Sättigung der PL-Löschung und auf Grund des Ausgleichs des Triplett-Transfers von Alq₃ zu DCM2 und des Triplett-Einfangens an ADN bestimmt. Das Einbringen von N₀ vermeidet die Komplikation der Behandlung eines individuellen Triplett-Transports in der ternären Mischung.To understand the dynamics of transient PL and laser operation, we refer to the previous work 'ENREF 8 to include the triplet Dexter transfer from host mixing to guest and guest triplet saturation. Therefore, the equations of the coupled laser rate are as follows:

where S, T _H , T _G , P are respectively guest singlet photon densities, host mixture triplet (including both ADN and Alq ₃ ), guest triplet and laser mode of operation, t is time, η is the pump emission fraction, which is absorbed by the organic layer, I is the pumping intensity, e _p = 3.06 eV is the pump photon energy, d = 200 nm is the thickness of the OSL gain medium, k _S = (6.7 ± 0.5) × 10 ⁸ s ^{-1 is} the natural rate of guest S decay (measured on a 2% DCM2: Alq ₃ layer excited by 1.5 ns wide N ₂ laser pulses), k _{ISC is} the host ISC rate , k _{ST is} the guest ST annihilation rate, γ = σ _stim S is the gain, σ _{stim is} the stimulated emission cross section, c is the speed of light, and n _eff = 1.6 and Γ = 0.69 the effective refractive index and optical confinement factor for the waveguide of SiO ₂ (n = 1.48) / organic (n = 1.82) / air (n = 1). ²⁴ Similarly, k _{HG is} the host-guest Dexter transfer coefficient, L is the guest-host van of the Waals radius (~ 1 nm), N ₀ is the guest triplet saturation population, α _CAV is the resonator loss with no contribution from the Triplet absorption, α _TT , and σ _TT is the guest triplet absorption cross section, and β ≈ 10 ^-4 is the spontaneous emission factor ²⁵ . For the PL we get P = 0, and the intensity is proportional to S. It is assumed that the host-triplet population does not interact with S or P; this is tested by data adjustments and triplet absorption measurements. Now N _{0 is determined} from the saturation of the PL quench and due to the compensation of the triplet transfer from Alq ₃ to DCM2 and the triplet trapping to ADN. The introduction of N ₀ avoids the complication of treating an individual triplet transport in the ternary mixture.

bestimmt. Somit steigt für T_G = 0,7 N₀ k_Dex nur von 7,6 × 10⁴/s (x = 0) auf 4,4 × 10⁵/s (x = 70) an, was mit der kürzeren PL-Löschzeit für ein höheres x übereinstimmt.The free parameters k _ST , k _ISC , k _HG and N _{0 are used} in the adaptation of the PL transients. To test model consistency, transients at four different pump intensities (1.6, 1.3, 0.93, and 0.56 kW / cm ² ) yield a single set of parameter values, summarized in Table 1. For all layers, k _ST = 2.0 × 10 ¹⁰ cm ³ / s, as is the case for guest ST annihilation due to the resonant Energy transport is expected, which depends only on the DCM2-S emission and T-absorption. As x increases, fewer triplets are transferred from Alq ₃ to DCM 2, and more of them will adhere to ADN; thus, N ₀ decreases from 5.0 × 10 ¹⁸ cm ^-3 to 9.2 × 10 ¹⁷ cm ^-3 when x = 70, resulting in decreased PL transient loss. The increase of ~ 10 ⁵ at k _HG seems surprising, but the Dexter transport rate is by

certainly. Thus, for T _G = 0.7 N ₀ k _Dex only increases from 7.6 × 10 ⁴ / s (x = 0) to 4.4 × 10 ⁵ / s (x = 70), which is consistent with the shorter PL Deletion time for a higher x matches.

To the laser operation transients in 2 B) To model, three additional parameters, σ _TT , σ _stim and α _CAV , are required. In this case, α _TT (λ) became Lehnhardt et al., Phys. Rev. B 81 (16), 165206 (2010) , (see EPAPS), and σ _TT = α _TT / N ₀ is shown in Table 1 at λ = 680 nm. The nearly constant α _TT (λ) spectra and σ _TT for all x are consistent with the assumption that only the guest triplet absorbs the laser emission (ie, host and manager absorption are negligible). Further, α _CAV = Γσ _stim S _PS , where S _PS = ηI _PS / (e _P dk _S ) is the threshold _threshold S population, where T accumulation is negligible for short excitation pulses. With these measurements and assumptions, the _{lasing transients are} adjusted using only a single free parameter, σ _stim (Table 1). It should be noted that the effect of ADN as a triplet manager is its ability to decrease N ₀ , while k _ST and σ _TT remain unchanged because they are intrinsic to DCM2.

The net gain g (t) = Γσ _stim (t) - α _CAV - Γσ _TT T _G (t) = 0 determines the dynamics of the threshold S population, S _TH (t), which in 3 for the Alq ₃ host (squares) and the optimized (x = 70) mixed host (asterisks) using the parameters from Table 1. Surprisingly, two separate threshold S populations emerge from the adjustments, with a CW threshold population (S _CW ) occurring at a density greater than that needed for pulsed laser (S _PS ) operation. Since t → 0, the triplet loss is

Γσ _TT T _G << α _CAV , giving S _PS = α _CAV / (Γσ _stim ). Over time, T _G increases and at the same time the associated loss increases until Γσ _TT T _G > α _CAV . Finally, T _{G reaches} its saturation density, N ₀ , at which the triplet loss can no longer increase, giving S _CW = (α _CAV + Γσ _TT N ₀ ) / (Γσ _stim ). 3 also shows S (t) for several pump intensities, I, for the host-manager mix, with the lasing time versus I being plotted in the drawer. Due to the saturation of T _G, and thus S _TH , with an I greater than the CW pump intensity threshold, I _CW = 2.2 kW / cm ² , the lasing duration is no longer affected by the triplet loss and tends to infinity. Table I also gives I _CW for all x in mixed hosts. With a larger N ₀ and thus an increased triplet loss, the OSL with Alq ₃ -Wirt I _CW = 32 kW / cm ² . Due to the damage of the organic layer at such high intensities, the CW laser operating threshold was not previously specified in the absence of a manager.

im Vergleich zur Impulsschwelle I_PS = I_CW(N₀ ≈ 0). Aus Gl. (5) ist I_CW eine quadratische Funktion der Gast-Triplett-Sättigungspopulation: k_STN₀ stammt aus der S-T-Löschung, welche die Verstärkung reduziert; und Γσ_TTN₀ ist auf die Triplett-Absorption zurückzuführen, was den Verlust erhöht.Disregarding the change in the singlet population due to the stimulated emission (see equation (1)), the CW threshold is approximately as follows:

in comparison to the pulse threshold I _PS = I _CW (N ₀ ≈ 0). From Eq. (5) I _{CW is} a quadratic function of the guest triplet saturation population: k _ST N ₀ is from the ST cancellation which reduces the gain; and Γσ _TT N ₀ is due to triplet absorption, which increases the loss.

To test for the presence of this CW state, a laser with Alq ₃ / ADN (x = 70) / DCM ^{2 was} excited to 2.4 kW / cm ² , or just above the calculated value of I _CW using the parameters in Table I. 3 , Inset left, shows a streak camera image of this emission over a duration of 20 microns. Laser operation becomes weaker (resulting in the apparent spectral narrowing), but does not shut off at the end of the long pulse, which is consistent with theory. In fact, a lasing life of approximately 100 μs was observed (see EPAPS) when pumped by a single pulse, although the degradation of the layer ultimately results in the lasing life due to the high optical pump intensities limits. Therefore, while this OSL significantly exceeded its CW threshold, the laser functions CW-like due to material degradation.

Interestingly, the blue wavelength of laser operation shifts from λ = 688.1 nm to 687.7 nm during the lasing period, 3 shown, inset left. Wavelength shifts have been observed with liquid dye lasers attributed to competition between triplet absorption and gain spectrum. For thin-film monomode DFB-OSL, where triplet absorption is broadly constant (see EPAPS), the shift is more due to changes in the effective refractive index with increasing T-density.

It should be noted that I _{CW can be} further reduced and laser uptime extended by using a more stable manager with lower triplet energy and with a better match between manager emission and guest absorption than achieved with ADN. Then, the lower saturation guest-triplet population contributes a negligible loss, where I _CW → I _PS . The structure concept can be applied to the later development of electrically pumped organic semiconductor lasers, with 75% of the injected electrons leading to triplets, compared to only a few percent in optical pumping.

Finally, the presence of a CW threshold at a higher pump intensity than the pulsed threshold seen in all previous OSL studies is shown. Based on our analysis, we demonstrate a lasing life of up to 100 μs by introducing a triplet manager into the OSL gain medium. The reduced triplet-induced loss of the triplet-managed OSL reduces I _CW from 32 kW / cm ² to a more useful value of 2.2 kW / cm ² , which is observed here.

MEASUREMENTS

The singlet energy is from the top of the PL spectrum in 4 (a) for ADN (S = 2.83 eV), Alq ₃ (S = 2.38 eV), and DCM2 (S = 2.03 eV). The spectral overlap of ADN and Alq ₃ -PL and DCM 2 absorption, together with DCM 2 emission in the lightly doped layers, demonstrates efficient and complete Förster transfer of singlets generated in both the host and the manager were, to the guest. The 17 nm bathochromic shift of the PL for the doped layer is due to the solid-state solvation effect.

The triplet energies of the three fluorescence molecules are determined using the method of Tanaka et al., Phys. Rev. B 71 205207 (2005) , measured. Due to the minor triplet emission of the fluorophores, the two phosphors are: tris (2-phenylpyridine) Ir (III) (Ir (ppy) ₃ ), T = 2.4 eV) and bis (2-phenylquinoline) (acetylacetonate) Ir (III) (PQIr), T = 2.1 eV) are doped together with the substance under study to allow efficient transfer of photogenerated triplets from the phosphorus to the fluorophores, thereby overcoming its low intersystem crossing rate. The triplet energy of the phosphorus is lower than that of the fluorophore singlet but higher than its triplet in order for the transfer to occur. The photoluminescence at 14 K of the mixtures:
Alq ₃ (25%) / Ir (ppy) ₃ (75%), DCM2 (50%) / PQIr (50%) and ADN (50%) / Ir (ppy) ₃ (50%) using an N ₂ - Pump lasers (1 ns pulse) are measured using a streak camera (Hamamatsu C4334). The spectra at 0.4 ms to 9 ms after the pump pulses are in 4 (b) shown. The triplet energies of Alq ₃ (T = 1.99 eV), DCM2 (T = 1.74 eV) and ADN (T = 1.69 eV) are taken from the fits to Gaussian functions (solid lines). The Alq ₃ triplet energy agrees with that of Tanaka et al., Phys. Rev. B 71 205207 (2005) , was achieved.

The triplet absorption is measured by a spatially separated pump-probe experiment, that of Lehnhardt et al., Org. Electron. 12 486 (2011) , is proposed. The pump pulse of a laser diode with λ = 405 nm has a duration of 50 μs, which saturates the guest triplet; the probe pulse of an N ₂ (wide 1.5 ns) laser is applied 100 ns after the pump has been switched off. The PL of the film is measured at the film edge either by a streak camera (Hamamatsu C4334) for measuring the absorption spectrum α _TT (λ) or by a band pass filter with λ = 680 ± 5 nm through an avalanche photodiode (C5658) for α _TT near the Wavelength of laser operation with little deviation levied. 5 shows the PL intensity of the probe with and without pump pulse for x = 0 and 70 layers. It can be seen that the triplet absorption is significantly reduced by the incorporation of the triplet manager. Out 5 be in 6 obtained two similar broad and featureless α _TT (λ), confirming that the absorptions from the same excited state come (guest triplet). As described above, the ~ 5-fold difference is due to the different guest triplet saturation population, N ₀ .

Improved ultra-bright fluorescent OLED efficiency

The inventors have also demonstrated improved efficiency in ultrahigh fluorescent organic light emitting devices by triplet management.

In particular, the inventors have demonstrated singlet-triplet (ST) quenching and thus enhanced quantum efficiency in ultraviolet organic light-emitting diodes (OLEDs) by reducing the guest triplet population by introducing a triplet manager molecule into the emissive layer (EML). For example, an OLED whose EML is the red fluorophore, 4- (dicyanomethylene) -2-methyl-6-julolidyl-9-enyl-4H-pyran, is transformed into the host, tris (8-hydroxyquinoline) Al (Alq ₃ ) is doped with the triplet manager, 9,10-di (naphtha-2-yl) anthracene. The manager triplet energy is lower than that of the host or dopant, resulting in effective triplet removal from the dopant without affecting the radiative singlet population. Measurements suggest the complete suppression of ST deletion using the triplet management strategy, resulting in an increase of more than 100% of external OLED quantum efficiency in steady state.

The loss of efficiency in fluorescent organic light-emitting diodes (OLEDs) has been attributed variously to the charge imbalance of singlet polaron (SP) quenching and singlet triplet (ST) quenching. In ST deletion, the reduction in efficiency is proportional to the product of the triplet (T) population and erasure rate. Since 75% of the injected charge leads to non-radiative triplet formation with a relatively long lifetime (typically> 1 ms) compared to radiating singlets (~ 1 to 10 ns), OLED triplets can reach a high density (> 10 ¹⁸ cm ^-3 ). Also, fluorescent OLEDs often use a laser dye as an emitter, which usually has a resonance between the S emission spectra and the T absorption, resulting in a large ST deletion rate. The combined large T population and high ST erase rate can reduce OLED efficiency.

The conventional emission layer (EML) of a fluorescent OLED consists of a conductive host and an emitting guest. Because the guest often has lower S and T energies than the host, the two excitonic species that form on the host are transferred to the guest where ST deletion occurs. One strategy to reduce erasure is to put a "triplet manager" molecule in the EML to collect triplets, as it would in 1 will be shown. If the T-Manager has a higher S and lower T-energy than the guest, it facilitates Förster's transfer of S-excitons to the guest and Dexter's transport of T-excitons from the guest to the manager, thus making the guest ST -Annihilation is potentially eliminated. The effectiveness of such a strategy is demonstrated in OLEDs with EMLs having a host of tris (8-hydroxyquinoline) Al (Alq ₃ ) containing 2% by vol of 4- (dicyanomethylene) -2-methyl-6-glolidolide -9-enyl-4H-pyran (DCM2) is doped. Diverse concentrations (0 ≦ x ≦ 70 vol%) of 9,10-di (naphtha-2-yl) anthracene (ADN) are mixed into the EML for T-management.

The OLEDs were made in vacuum (~ 10 ^-7 Torr) by thermal evaporation on pre-patterned indium tin oxide (ITO) coated glass substrates according to standard procedures. The 25 nm thick EML is sandwiched between a 35 nm thick hole transport layer (HTL) of 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl (NPD) and a 25 nm electron-transport layer of bathocuproin ( BCP) inserted. The array of 1 mm ² devices is completed by depositing a 0.8 nm thick LiF and a 100 nm thick Al layer through a shadow mask to define the cathodes. The steady state current density-voltage-luminance (JVL) characteristics were measured at <0.3 A / cm ² using a parameter analyzer and a calibrated Si photodetector. At higher currents of 0.1 to 2.5 A / cm ² , the intensity of electroluminescence (EL) was measured using a pulse generator (100 μs pulse width) and an avalanche photodiode.

It will be referred to again 4 (a) showing the photoluminescence (PL) spectra of the ADN and Alq ₃ layers and the EL spectra for OLEDs with EMLs with x = 0 and 50% ADN. The spectral overlap of the PL with the DCM2 absorption (shaded) and the pure DCM2-OLED emission confirm the complete Förster transfer of the singlets to the guest. The triplet energies of the three molecules are measured at 14 K using the method of triplet energy transfer from a sensitizing iridium complex. Out 4 (b) For example, the inventors measured triplet energies of Alq ₃ (T = 1.99 eV), DCM 2 (T = 1.74 eV) and ADN (T = 1.69 eV) associated with the in 1 match the requirements shown.

The proof that ADN suppresses the triplet transfer to DCM2 is obtained from the triplet absorption coefficients (x _r ) for 200 nm thick layers of 2% DCM2 doped into SiO ₂ in ADN and Alq ₃ 8th (Inset), derived. The triplet state is occupied by intersystem crossing with the singlet with a pump laser diode of 1.6 kW / cm ² , 50 μs, wavelength λ = 405 nm, and the absorbance is measured by transfer of the PL, which is from a N ₂ Laser pulse is excited with 5 μJ / cm ² , 1.5 ns λ = 337 nm, which is delayed by 100 ns with respect to the pump. Since x _r = σ _T T _G , where σ _{T is} the guest triplet absorption cross section and T _{G is} its density, the elimination of x _r by ADN is due to a successful removal of the triplets from DCM 2. Furthermore, the negligible excited state absorption for the DCM2 doped ADN layer also shows that the ADN triplet absorption in the DCM2 PL spectral region disappears.

8 (a) shows the transient EL for a series of OLEDs with different ADN fractions, x, after the start of a current step with J = 2 A / cm ² . For the controller (x = 0), the EL quickly peaks and then decays to a steady state intensity of ~ 50% of its initial value over the next 20 μs. Since the EL intensity is proportional to the S density, the transient decay is an indication of the ST erasure. After the onset of the current pulse, the S population quickly approaches its peak in the absence of triplets. As the current is maintained, the long-lived triplet population (~ ms) increases, resulting in increased ST deletion and thus a decreased S population. Finally, as the guest T-population approaches steady state, ST deletion also stabilizes, resulting in a reduced steady-state S population.

In the presence of the T-manager, the amount of transient decay of the EL is reduced with increasing x and disappears at x ≥ 50%, indicating complete suppression of the ST erasure. 9 shows the ratio of the EL intensity peak to the steady state, ρ (J) for the OLEDs 8 (a) , It was determined that ρ (J) decreases with increasing manager concentration, and ρ (J) = 1 for x ≥ 50%, which equates to zero transient decay.

wobei b der Ladungsungleichgewichtsfaktor ist, e die Elektronenladung ist, d die EML-Dicke ist, wenn man davon ausgeht, dass die Exzitonen über diese Schicht einheitlich verteilt sind, τ_s die natürliche Abklingzeit der Singuletts ist, und k_st die S-T-Löschungsrate ist. Ebenso sind k_HG und L jeweils der Koeffizient der Triplett-Transferrate von Wirt zu Gast bzw. der Vander-Waals-Radius, und N_GT(J) ist die Sättigungs-Gast-T-Population; d. h. wenn T_G(t) → N_GT(J) stoppt der Transfer und dT_G/dt = 0. Diese Behandlung geht von 25% injizierten Ladungen von Singuletts aus. Die Exponentialfaktoren sind auf den Diffusionstransport von Exzitonen zwischen Molekülen zurückzuführen, was mit dem Dexter-Prozess übereinstimmt. Schließlich ist T_H auf Grund der Triplett-Triplett-(T-T)Löschung und des natürlichen Abklingens gesättigt, doch diese Prozesse sind viel langsamer (~1 ms) als das interessante Zeitfenster (~30 μs) und werden deshalb vernachlässigt. Eine Singulett-Singulett-(S-S)Löschung wird nicht in Betracht gezogen, da sie bei solch niedrigen Dichten geringfügig ist. Schließlich ist auch eine S-P-Löschung möglich; sie kann jedoch nicht zu den beobachteten EL-Transienten führen, da die Polarondichte den Dauerzustand innerhalb von mehreren zehn ns nach dem Beginn des Stromimpulses erreicht.Two processes dominate the energy transport in triplet-managed OLEDs, namely the guest ST deletion, S + T _G → S _o + T _G (thus, the ground state), and the triplet-dexter transport from host to guest, T _H (includes both Alq ₃ and ADN triplets). The EL can be modeled using:

where b is the charge imbalance factor, e is the electron charge, d is the EML thickness, assuming that the excitons are uniformly distributed throughout this layer, τ _{s is} the natural decay time of the singlets, and k _{st is} the ST extinction rate , Similarly, k _HG and L are each the host-to-guest triplet transfer coefficient or Vander-Waals radius, and N _GT (J) is the saturation guest T population; ie, when T _G (t) → N _GT (J), the transfer stops and dT _G / dt = 0. This treatment is based on 25% injected charges of singlets. The exponential factors are due to the diffusion transport of excitons between molecules, which is consistent with the Dexter process. Finally, T _{H is} saturated due to triplet triplet (TT) quenching and natural decay, but these processes are much slower (~ 1 ms) than the interesting time window (~ 30 μs) and are therefore neglected. Singlet singlet (SS) erasure is not considered because it is marginal at such low densities. Finally, a SP deletion is possible; however, it can not lead to the observed EL transients since the polar density reaches the steady state within tens of ns after the start of the current pulse.

Assuming the boundary condition that T _G = 0 at t = 0, and T _G = N _GT , since t → ∞ in Eq. (1), ρ (J)

The damping of the external quantum efficiency is then given by EQE (J) = η _o η _C (J) η _T (J), where η _{o is} the external quantum efficiency (EQE) with perfect charge compensation and without singlet cancellation, η _C (J ) is the attenuation due to the charge imbalance and the SP cancellation, and η _T (J) = 1 / ρ (J) is the attenuation due to the ST cancellation.

From the PL transients measured for 50 nm thick layers using an N ₂ laser pump, τ _s = 1.5 ± 0.2 ns for DCM2: ADN / Alq ₃ , regardless of the manager concentration. For a DCM2 concentration of 2% by volume, L≈3 nm, as determined from the average spacing between the dopant molecules. With the edition for N _GT (J), which is given by Eq. (4), and for a perfect charge balance (b = 1), the EL transients are given by Eqs. (1) to (3) adjusted as the solid lines in 8 (a) demonstrate. From the adjustments, k _ST = 1.5 x 10 ^-10 cm ³ / s, regardless of host and manager concentrations, and is similar to the previous values achieved for DCM: Alq ₃ . In addition, it has been found that k _HG = 2.5 × 10 ⁷ s ^-1 for x = 0 and 10%, and k _HG = 3 × 10 ⁸ s ^-1 for x = 30% ADN.

With these adjustments, N _GT is calculated using Eqs. (4), with the results also found in 9 be specified. Obviously, introducing the triplet manager significantly reduces N _GT . For example, at J = 0.5 to 2.5 A / cm ² , N _GT (J) becomes from 4 x 10 ¹⁸ cm ^-3 (x = 0) to <3 x 10 ¹⁷ cm ^-3 (x = 30%) and 0 cm ^-3 (x ≥ 50%) reduced.

10 (a) shows EQE (J) for different concentrations of ADN. For x = 0 to 50%, EQE at low J (<10 ^-4 A / cm ² ) is similar to ~ 3%, while EQE attenuation is reduced to J at higher x. At high currents (J> 0.1 2.5 A / cm ² ), the EQE at x = 50% is increased by more than 100% compared to x = 0 due to the reduced attenuation. The separate contributions from the attenuation induced by polarons and triplets are in 10 (b) located. Here, η _T (J) is obtained from ρ (J), while η _C (J) is solved by assuming η _o = 3%, which is obtained at J → O. Out 10 (b) Reduced ST deletion is the major contributor to the improved EQE at x = 50%, while polar-induced attenuation at x = 50% is also slightly reduced due to bipolar charge transport in ADN. That is, although both ADN and Alq _{3 are} good electron-transporting agents, ADN has higher hole mobility. This can lead to a more efficient recombination and thus to a lower density of free charge carriers in the EML. This in turn reduces the SP cancellation and thus slightly increases η _C (J).

In contrast, the EQE decreases as x increases from 50% to 70%, though in both cases ρ = 1. This is attributed to a reduced η _C (J) at x = 70% due to charge imbalance. Since the deepest unoccupied orbital of a molecule (LUMO) of NPD is at 2.3 eV, the electron blocking barrier at the HTL / EML interface is smaller for ADN (with a LUMO at 2.6 eV) than for Alq ₃ (LUMO = 3.1 eV). Thus, at high concentrations of ADN, electron transport preferentially occurs on ADN and they more easily escape from the EML without recombination. This goes out 10 (a) , Inset, where x = 70% shows a much stronger current at x <50%. Thus, the host (Alq ₃ ) can not be completely replaced by the triplet manager to ensure that charge balancing is maintained.

T.-H. Liu, C.-Y. Iou and CH Chen, Curr. Appl. Phys. 5 (3), 218 (2005) , incorporated herein by reference in their entirety, use ADN and rubrene as co-hosts in an OLED based on the fluorophore, 4- (dicyanomethylene) 2-t-butyl-6- (1,1,7,7-tetramethyljulolidyl-9 -enyl) -4H-pyran (DCJTB), which is doped in Alq ₃ to reduce the attenuation of the strong steady state EQE. The improved EQE was explained by a reduced quenching of the singlet charge (Alq ₃ ^- ). The analysis of the inventors differs from that of Liu et al. where the transient efficiency indicates that reduced ST extinction is the main cause of the improved EQE. It is understood that rubrene (T = 1.1 eV (shown at M. Montalti, A. Credi, L. Prodi, and MT Gandolfi, "Handbook of Photochemistry," 3rd Edition (CRC, Boca Raton, FL., 2006) p. which is fully incorporated herein by reference)) can also be effectively used as a triplet manager, although data for rubrics: Alq ₃ : DCM2 devices are omitted for clarity.

Finally, the inventors have demonstrated that triplet managers mixed into the EML of fluorescent OLEDs can lead to a significant increase in quantum efficiency at high current density. The manager molecules promote efficient triplet transfer from the guest, thereby reducing S-T quenching at high current levels. Such a management strategy is generally applicable to fluorescent OLEDs that undergo S-T cancellation to achieve very high brightness, and has also been shown to be effective to allow organic semiconductor lasers to enter the continuous wave mode of operation.

Previous studies have shown that triplet-induced losses, which include both singlet-triplet quenching and triplet absorption, are significant impediments to electrically pumped organic semiconductor (OSL) lasers. In light of the above, a triplet management method is provided that could eliminate (or reduce) the triplet-induced losses in OSLs, thus opening a new path for the development of electrically pumped OSLs.

The triplet induced losses in conventional OSLs (including both small molecules and polymers) are due to the spectrum overlap of the laser emission and the triplet state absorption. The triplet management strategy involves doping the laser enhancement medium with an additional molecule, the so-called triplet manager, which may have the following characteristics: 1. the triplet energy of the host is smaller than that of all other molecules already present in the enhancement medium were; 2. the triplet absorption of the manganese at the wavelength of laser operation is negligible. Once these two features are met, the triplet-induced loss can be eliminated or significantly reduced. The effectiveness of using 9,10-di (naphtha-2-yl) anthracene (ADN) or rubrene as a triplet manager in the conventional small-molecule guest-host amplification medium of 4- (dicyanomethylene) -2-methyl- 6 Julolidyl-9-enyl-4H-pyrane (DCM2) -doped tris (8-hydroxyquinoline) aluminum (Alq ₃ ) was previously detected. By optical pumping, the laser managed with ADN has a lasing life of nearly 100 μs, compared to only 400 ns of the conventional unmanaged laser.

Using the same triplet management strategy in the emissive layer (EML) of a fluorescent organic light emitting diode (OLED), the inventors have discovered complete suppression of triplet-induced loss, and thus efficiency improvements of greater than 100%. Again, this was demonstrated using ADN or rubrene as the triplet manager in the DCM2-doped Alq ₃ -EML of an OLED.

As provided herein, the inventors have found that the two approaches described above for an electrically pumped OSLS could be combined. A laser consists of a gain medium and a feedback structure. The gain medium of the electrically pumped OSL uses a triplet management strategy, e.g. A triplet manager molecule doped into an otherwise conventional polyfluorene or small molecule guest-host system. The feedback structure may have any suitable shape, such as the examples shown in FIG 11 (a) to (d) are provided. For example, shows 11 (a) a feedback with a planar waveguide, wherein the feedback is provided by the reflection from the edge surface. 11 (b) shows Distributed Feedback (DFB), where the feedback is provided by the diffraction of the grating. 11 (c) Figure 11 shows the feedback with a planar distributed Bragg reflector (DBR), the feedback being provided by the reflection from the DBR parallel to the substrate. 11 (d) shows the surface emitter structure (VCSEL), where the feedback results from reflection from the front and back mirrors. However, as one of ordinary skill in the art would appreciate after reading the present disclosure, any suitable feedback system or device may be used.

In general, the choice of material and thickness for the anode, the hole injection layer (HTL), the electron injection layer (ETL), and the cathode in an OSL can be as in conventional OLEDs. The thickness of the gain medium may be in the range of 50 nm to 300 nm. The substrate should preferably have a refractive index that is lower than organic layers (n ~ 1.6 to 1.8), and is typically quartz or SiO ₂ , but may include any material. In the exemplary feedback structures used in 11 (a) to (c), the feedback is parallel to the substrate; whereas in the exemplary structure shown in FIG 11 (d) is shown, the feedback is perpendicular to the substrate.

gegeben, wobei t die Zeit ist, g die Nettoverstärkung ist, Γ der optische Einschlussfaktor ist, σ der stimulierte Emissionsquerschnitt ist, α der Resonatorverlust ist, σ_TT der Triplett-Absorptionsquerschnitt ist, und S und T jeweils Singulett- und Triplett-Dichten sind. Nun können mit den Triplett-Managern die triplettinduzierten Verluste eliminiert werden, also:

wobei d die Dicke des Verstärkungsmediums (EML-Dicke bei OLED) ist, e die Elektronenladung ist, und τ die Singulett-Lebensdauer ist. Dann ist die Schwellenstromdichte J_th = 4edα/Γτα (es sei zu beachten, dass α und Γ nicht unabhängig sind). Mit typischen Werten von d = 50 nm, Γ = 0,3, α = 10 cm^–1, τ = 2 ns und σ = 4 × 10^–17 cm² kann man dann berechnen, dass J_th = 1,3 kA/cm². Gemäß früheren Untersuchungen ist eine derart hohe Stromdichte im Allgemeinen bei organischen Halbleiterstoffen zu erreichen. Falls Triplett-Verluste vorliegen, sind die Schwellenstromdichten wesentlich höher (siehe N. C. Giebink und S. R. Forrest, „Temporal response of optically pumped organic semiconductor lasers and its implication for reaching threshold under electrical excitation”, Phys. Rev. B 79 (7), 073302 (2009) 3(b), hiermit durch Bezugnahme vollständig mit eingeschlossen).The threshold current density of the lasing operation for the exemplary electrically pumped OSLs can be calculated as follows. The threshold condition is through:

where t is the time, g is the net gain, Γ is the optical confinement factor, σ is the stimulated emission cross section, α is the resonator loss, σ _{TT is} the triplet absorption cross section, and S and T are each singlet and triplet densities , Now triplet managers can eliminate triplet induced losses, so:

where d is the thickness of the gain medium (EML thickness at OLED), e is the electron charge, and τ is the singlet lifetime. Then the threshold current density J _th = 4edα / Γτα (note that α and Γ are not independent). With typical values of d = 50 nm, Γ = 0.3, α = 10 cm ^-1 , τ = 2 ns and σ = 4 × 10 ^-17 cm ² , one can then calculate that J _th = 1.3 kA / cm ² . According to previous investigations, such a high current density can generally be achieved with organic semiconductor materials. If there are triplet losses, the threshold current densities are much higher (see NC Giebink and SR Forrest, "Temporal Response of optically pumped organic semiconductor lasers and their implication for reaching threshold under electrical excitation", Phys. Rev. B 79 (7), 073302 (2009) 3 (b) hereby incorporated by reference in its entirety).

In addition to the triplet loss, contact loss and polaron loss are also considered as impediments to electrically coupled OSL. A recent investigation at M. Reufer, S. Riechel, JM Lupton, J. Feldmann, U. Lemmer, D. Schneider, T. Benstem, T. Dobbertin, W. Kowalsky, A. Gombert, K. Forberich, V. Wittwer and U. Scherf , "Lowthreshold polarized feedback laser with metallic contacts", Appl. Phys. Lett. 84 (17), 32623264 (2004) on page 8 and fully incorporated herein by reference, showed that contact loss can be eliminated by carefully tuning the waveguide mode. Polaron absorption has previously been measured in a similar way to triplet absorption, but it can be mitigated by using highly conductive materials to reduce the polaron concentration. This is because the polaron population decreases in equilibrium when the mobility is increased by: n α 1 / √μ, where μ is the mobility of the layer.

embodiments

A first device is provided. The device comprises an organic semiconductor laser. The organic semiconductor laser further includes an optical resonator and an organic layer disposed in the optical resonator. The organic layer comprises: an organic host compound; an organic emissive compound that is fluorescently emissive; and an organic dopant compound. The organic dopant compound may also be referred to herein as a "triplet manager". The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound. The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic emissive compound. The singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound.

The described energy relationships enable the organic dopant compound to derive triplets of the organic host compound and the organic emissive compound and to avoid the transfer of triplets from the organic dopant compound to other compounds. The organic dopant compound also preferably has a triplet lifetime which is short relative to the organic host compound and the organic emissive compound such that the organic dopant compound can dissipate many triplets over a period of time.

Triplet and singlet energies for many different compounds are readily available in the literature. Part of this literature is described here. These energies can be measured and can also be calculated. There may be certain differences in the values achieved through various measurement and calculation techniques. For the purpose of comparing the energies to see if one is larger or smaller than the other, it is preferred that the same or a similar measurement or calculation be used to obtain the values to be compared. If a particular measurement or calculation tends to over-or under-value energy values, using the same measurement or calculation to achieve all the values compared minimizes any such effect.

The use of the term "or equal to" with respect to the singlet energy of the organic emissive compound as compared to the singlet energy of the organic host compound is intended to take into account the possibility of endothermic transfer. These endothermic processes are in the U.S. Patent No. 2005/0214576 described in more detail on May 3, 2005, which is hereby incorporated by reference in its entirety. Thus, while it may generally be preferred that the singlet energy of the organic emissive compound be less than the singlet energy of the organic host compound, the embodiments are not necessarily limited thereto.

According to some embodiments of the above-described first device, the organic semiconductor laser may further comprise a hole injection layer disposed between the anode and the hole transport layer and an electron injection layer disposed between the cathode and the electron transport layer. As noted previously, the device (and / or the OSL) may include some or all of the organic layers typically used in conventional OLEDs.

Preferably, the singlet energy of the organic emissive compound is less than the singlet energy of the organic dopant compound.

This energy ratio minimizes the transfer of singlets from the organic emissive compound to the organic dopant compound such that the singlets of the organic emissive compound can emit a photon as desired.

Preferably, the organic dopant compound does not strongly absorb the fluorescence emission of the organic emissive compound.

When it is said that the dopant compound "does not strongly absorb" the fluorescent emission of the emitting compound, it means that the ground state and the singlet excited and triplet triplet excited states all have a low absorption of the spectrum emitted from the fluorescent emitting compound , One skilled in the art can determine if there is low absorption by looking at representations of the emission and absorption spectra on the same graph and checking for substantial overlap - a small overlap in end regions is allowed.

In one embodiment, the first device further includes an optical pump optically coupled to the organic layer.

According to one embodiment, the organic semiconductor laser further comprises an anode and a cathode. The organic layer is disposed between the anode and the cathode. A hole transport layer is disposed between the organic layer and the anode. An electron transport layer is disposed between the organic layer and the cathode. The organic dopant compound is present only in the emission layer.

Preferably, the triplet decay time of the dopant compound is shorter than the triplet decay time of the emitting compound.

Preferably, the concentration of the doping compound is 10 to 90% by weight, and the concentration of the emitting compound is 0.5 to 5% by weight.

In one embodiment, the host may be completely absent in the organic layer, i. H. the organic layer includes only the emitting compound and the doping compound. In this case, the concentration of the emitting compound is preferably 0.5 to 5% by weight, with the remainder of the layer being the doping compound. The preferred energy level relationships described herein for the dopant compound and the emissive compound also apply to this embodiment. The device may comprise other organic layers, such as hole transport and electron transport layers - the present embodiment relates to a two-component emissive layer comprising the dopant and the emissive compound, but the remainder of the device may comprise any of the components described herein.

Preferably, the organic emissive compound is capable of fluorescence emission at room temperature.

Preferably, the doping compound is selected from the group comprising: anthracene, tetracene, rubrene and perylene and their derivatives. More preferably, the doping compound is selected from anthracene, and its derivatives are particularly preferred. More preferably, the doping compound is ADN.

According to some embodiments, the dopant compound is a phosphor. According to some embodiments, the dopant compound is a fluorophore.

It is preferred to maximize the transfer of host and dopant singlets to the emitting compound. The common system of host and dopant (without emitting compound) may have different emission spectra for different dopant concentrations. For optimized concentration, the overlap between this emission spectrum and the guest absorption spectrum is maximized. The result of such maximization is increased or even complete singlet transport to the emitting compound. This is a more accurate condition than the condition that the singlet energy of the emitting compound is simply less than the singlet energy of the host and the singlet energy of the dopant.

It is preferred to maximize the transfer of triplets from the host and the emissive compound to the dopant. Higher dopant concentration results in a more efficient triplet transfer of emissive compound and host to the dopant. It is a more specific condition than the condition that the triplet energy of the dopant is less than or equal to the triplet energy of the host and the emitting compound. However, if the dopant concentration is too high, the transport of singlets to the emitting compound may be impaired. Also, too high dopant concentration can lead to faster degradation of the device.

In embodiments where the laser is pumped electrically, i. H. where the emissive layer is between an anode and a cathode, it is also preferable to select the concentrations of the emissive compound, the host and the dopant so as to obtain the highest mobility of the emissive layer.

According to some embodiments, the triplet energy of the dopant compound is preferably greater than 1.3 eV, and more preferably greater than 1.6 eV. 130 kJ / mol is about 1.3 eV. If the triplet energy of the host material is high enough, the triplet energy of the triplet sink dopant may also be high. Anthracene (triplet exciton 1.6 eV) as a triplet sink in Alq ₃ is just one example. The use of high energy materials as described herein enables hosts capable of supporting high energy fluorescent emitters, such as blue emitting emitters. Since the technology for organic emissive compounds is generally weaker for blue emitters, the use of high energy hosts and triplet sinks to improve the performance of blue emitting fluorescent laser devices is a particularly desirable result. According to a particularly preferred embodiment, the triplet energy of the dopant compound is at least 1.3 eV, preferably at least 1.6 eV, and not more than 1.7 eV, for the reasons described herein.

The first device may be a consumer product. In the context of the present application, such a consumer product comprises any commercially available product comprising a laser. Examples include printers, communication devices, CD / DVD devices, and many other well-known products. One skilled in the art can readily use the lasers described herein instead of the conventional lasers already used in such consumer products.

According to some embodiments of the first device as described above, the organic semiconductor laser may further include a feedback structure. The feedback structure may be configured to reflect (or otherwise deflect or direct) photons having a specific wavelength and phase to return through the gain medium (i.e., the laser operating medium). The feedback structure may include at one or both ends a partially transmissive surface that allows some of the photons to be transmitted through the interface (whereas the remaining photons may be reflected or otherwise conducted back through the gain medium). According to some embodiments, the feedback structure may include one or more mirrors (eg, a semi-mirrored surface) and / or diffraction gratings. According to some embodiments, the feedback structure may include any or some combination of a planar waveguide structure, a distributed feedback structure, a Bragg reflector feedback structure, or a surface emitter structure (VCSEL). However, any suitable feedback structure may be used in the embodiments disclosed herein, as will be understood by those skilled in the art. For example, in some embodiments of the first device described above, the organic semiconductor laser may further comprise a substrate. The anode of the device may be disposed over the substrate, and at least one mirror is disposed between the substrate and the anode.

A method is provided. An organic semiconductor laser is provided. The organic semiconductor laser further includes an optical resonator and an organic layer disposed in the optical resonator. The organic layer comprises: an organic host compound; a organic emissive compound capable of fluorescence emission; and an organic dopant compound. The organic dopant compound may also be referred to herein as a "triplet manager". The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound. The triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic emissive compound. The singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound. The organic semiconductor laser is pumped to achieve laser operation.

According to some embodiments of the method described above, the singlet energy of the organic emissive compound is less than the singlet energy of the organic host compound.

In one embodiment, the pumping is optical pumping.

According to one embodiment, the pumping is an electric pump.

When the organic semiconductor laser is pumped, laser operation is achieved for at least 1 microsecond.

According to some embodiments, the organic semiconductor laser is pumped at a power exceeding the pulse threshold.

According to some embodiments, the organic semiconductor laser is pumped at a power exceeding the CW threshold.

In one embodiment, the organic semiconductor laser is pumped at a power that exceeds the continuous wave threshold for at least 1 microsecond, and more preferably at least 100 microseconds.

It should be understood that the various embodiments described herein are exemplary only and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be replaced with other materials and structures without departing from the spirit of the invention. The present invention as claimed may therefore involve variations from the specific examples and preferred embodiments described herein, as will be apparent to those skilled in the art. It should be understood that various theories why the invention works and the modeling of specific configurations are not intended to be limiting.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

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Claims (22)

First device, further comprising: an organic semiconductor laser, further comprising: an optical resonator; an organic layer disposed in the optical resonator, the organic layer comprising: an organic host compound; an organic emissive compound capable of fluorescence emission; and an organic dopant compound; in which: the triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound; the triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic emitting compound; the singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound. The first device of claim 1, wherein the singlet energy of the organic emissive compound is less than the singlet energy of the organic host compound, or wherein the singlet energy of the organic emissive compound is less than the singlet energy of the organic dopant compound. The first device according to claim 1, wherein the organic dopant compound does not strongly absorb the fluorescence emission of the organic emissive compound. The first device of claim 1, further comprising an optical pump optically coupled to the organic layer. The first device according to claim 1, wherein the organic semiconductor laser further comprises: an anode; a cathode; wherein the organic layer is disposed between the anode and the cathode; a hole transport layer disposed between the organic layer and the anode; and an electron transport layer disposed between the organic layer and the cathode; wherein the organic dopant compound is present only in the emission layer. The first device of claim 1, wherein the triplet decay time of the dopant compound is shorter than the triplet decay time of the emitting compound. The first device of claim 1, wherein: the concentration of the doping compound is 10 to 90% by weight; the concentration of the emitting compound is 0.5 to 5% by weight. The first device of claim 1, wherein the organic emissive compound is capable of fluorescence emission at room temperature. The first device of claim 1, wherein the dopant compound is selected from the group consisting of: anthracene, tetracene, rubrene and perylene and their derivatives. The first device of claim 1 wherein the dopant compound is selected from anthracene and its derivatives, preferably the dopant compound is ADN. The first device of claim 1, wherein the dopant compound is a phosphor or a fluorophore. The first device of claim 1, wherein the first device is a consumer product. A method comprising the steps of: providing an organic semiconductor laser, further comprising: an optical resonator; an organic layer disposed in the optical resonator, the organic layer comprising: an organic host compound; an organic emissive compound capable of fluorescence emission; and an organic dopant compound; wherein: the triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic host compound; the triplet energy of the organic dopant compound is less than or equal to the triplet energy of the organic emitting compound; the singlet energy of the organic emissive compound is less than or equal to the singlet energy of the organic host compound; Pumping the organic semiconductor laser to achieve the laser operation. The method of claim 13, wherein the singlet energy of the organic emissive compound is less than the singlet energy of the organic host compound. The method of claim 13, wherein the pumping is optical pumping or electric pumping. The method of claim 13, wherein the lasing operation is achieved for at least 1 microsecond. The method of claim 13, wherein the organic semiconductor laser is pumped at a power exceeding the pulse threshold. The method of claim 13, wherein the organic semiconductor laser is pumped at a power exceeding the continuous wave threshold, or the organic semiconductor laser is pumped at a power exceeding the CW threshold for at least 1 microsecond, or the organic semiconductor laser is pumped at a power exceeding the CW threshold for at least 100 microseconds. The first device according to claim 5, wherein the organic semiconductor laser further comprises: a hole injection layer disposed between the anode and the hole transport layer; and an electron injection layer disposed between the cathode and the electron transport layer. The first device of claim 5, wherein the organic semiconductor laser further comprises a feedback structure. The first device of claim 5, wherein the feedback structure comprises any or some combination of: a planar waveguide structure; a distributed feedback structure; a feedback structure with Bragg reflector; or a surface emitter structure (VCSEL) includes. The first device of claim 5, wherein the organic semiconductor laser further comprises a substrate, wherein: the anode is disposed above the substrate; and at least one mirror is disposed between the substrate and the anode.

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