S. W. Jessen

Alternating‐current light‐emitting devices based on conjugated polymers

Most polymer electroluminescent devices to date are represented as tunnel diodes and operate under direct‐current (dc) driving field. Here we report the fabrication of symmetrically configured alternating‐current (ac) light‐emitting (SCALE) devices based on conjugated polymers. The new devices consist of an emissive polymer layer sandwiched between two redox polymer layers. This configuration enables the SCALE devices to work under both forward and reverse dc bias as well as in ac modes. The nearly ohmic electrode/redox polymer contacts improve the charge injection efficiency significantly and make the SCALE device operation insensitive to electrode work functions. Symmetric operation supports the key role of redox polymer/emissive polymer interface states.

EXCIPLEX EMISSION IN BILAYER POLYMER LIGHT-EMITTING DEVICES

Photoluminescent and electroluminescent studies of bilayer heterojunctions formed from a poly(pyridyl vinylene phenylene vinylene) (PPyVPV) derivative and poly(vinyl carbazole) (PVK) show an emission peak which cannot be ascribed to either the PPyVPV derivative or PVK layer. Through studies of absorption and photoluminescence excitation (PLE) spectra we demonstrate that the additional feature results from an exciplex at the bilayer interface. The photoluminescence efficiency of the exciplex is greater than 20%. The electroluminescence spectrum from the bilayer devices is entirely due to exciplex emission, with internal efficiencies initially achieved exceeding 0.1%.

Blue electroluminescent devices based on soluble poly(p‐pyridine)

We have fabricated unilayer electroluminescent devices from soluble poly(p‐pyridine) (PPy). The solubility of PPy in weak acids allows direct spin casting of the polymer films. The electroluminescence spectrum peaks at 2.5 eV (497 nm) corresponding to white light weighted towards the blue end of the spectrum. The photoluminescence spectrum peaks at 2.35 eV (530 nm). The operating voltages of the devices ranged from 4 to 12 V with current densities of 6 to 8 mA/mm2. We compare our devices with similar blue emitting devices based on poly(p‐phenylene).

Poly (p-pyridine) - and poly (p-pyridyl vinylene) -based polymers: their photophysics and application to SCALE devices

Abstract Photophysics and light-emitting device applications of poly ( p -pyridine) - and poly( p -pyridyl vinylene)-based polymers are presented. Extensive time-resolved (ps to ms) photoluminescence, stimulated emission and photoinduced absorption studies of solutions, powders and films demonstrate that the primary photoexcitation of these polymers is an intrachain singlet exciton. The presence of (n,π * ) states leads to enhanced intersystem crossing to triplet excitons for the powder form, while aggregate formation plays a key role in the films. Polarons are important at longer times. These polymers were used to fabricate ‘conventional’ polymer light-emitting diodes. In addition, these polymers were used to demonstrate a novel light-emitting structure, the symmetrically configured a.c. light-emitting (SCALE) device. These new devices have potential advantages in their use with high workfunction electrodes, such as gold, and also in their a.c. operation.

Absorption and luminescence of pyridine-based polymers

We summarize the low energy photophysics of the pyridine-based polymers poly(p-pyridine)(PPy), poly(p-pyridyl vinylene) (PPyV) and copolymers made up of PPyV and poly(p-pheneylene vinylene) (PPyVPV). The absorption and luminescence properties are morphology dependent. The primary photoexcitations within these polymers are singlet excitons which may emit from individual chains following a random walk to lower energy segments, depending upon the excitation energy. Films display redshifted absorption and emission properties with a decrease in photoluminescence efficiency which can be attributed to aggregate formation in comparison to powder and solution forms. Photoinduced absorption (PA) studies show direct conversion of singlet to triplet excitons on the ps time scale. Polaron signatures and the transition between triplet exciton states are seen in powder forms using ms PA techniques. Film forms display only a polaron signature at millisecond times indicating that morphology plays a key role in the long-time photophysics for these systems. Photoluminescence detected magnetic resonance studies also have signatures due to both polarons and triplet excitons. The size of the triplet exciton is limited to a single ring suggesting that the triplet exciton may be trapped by extrinsic effects.

Exciplex emission in heterojunctions of poly(pyridyl vinylene phenylenevinylene)s and poly(vinyl carbazole)

Abstract We present photoluminescence and electroluminescence spectra of heterojunctions formed from poly(vinyl carbazole) (PVK) and poly(pyridyl vinylene phenylene vinylene) (PPyVPV). Bilayers of PVK and PPyVPV show a photoluminescence peak which cannot be assigned to either the PVK or the PPyVPV layer. Absorption spectra show that the additional feature results from an exciplex at the bilayer interface. The electroluminescence spectrum from the heterojunctions is due to exciplex emission, with internal efficiencies of ~ 0.1–0.5%.

Litho/Design Co-Optimization and Area Scaling for the 22-nm Logic Node

We present a comprehensive study of area scaling for 22nm-logicnode routed metal/via layers as a function of route pitch and patterning strategy in both single-exposure (SE) and doublepatterning (DP) regimes. For each candidate route pitch (8856nm), we determine an optimal illumination scheme and develop layout rules for the metal layers. A perturbative area model is used to approximate the impact of the candidate rule set on area scaling. For the most promising SE case, we apply a novel ‘source/design optimization’ technique to further optimize illumination and rules, wherein we extend the source-mask optimization approach (1) by allowing design rules to vary in the analysis. We demonstrate that the optimal area scaling achievable with DP techniques can be vastly superior to SE, and therefore may justify the associated additional cost per wafer.

Five-layered symmetrically configured ac light-emitting (SCALE) devices and their three-layered variations: use of gold as an electron and hole injection electrode

Symmetrically configured ac light-emitting (SCALE) devices based on conjugated polymers utilizing indium-tin oxide (ITO) and aluminum as electrodes have been demonstrated recently. Here we report the fabrication of SCALE devices using a more stable high workfunction metal, such as gold, as a charge (both electron and hole) injection electrode. Also, a variation of such devices in which the electroluminescent polymer, instead of being separated from the insulating polymer, is dispersed in the insulating polymer to form a unified emitter-insulator is reported. These devices emit light in both forward and reverse dc bias with symmetric current- voltage characteristics. Under low frequency ac (sinusoidal) driving voltage, light pulses with double the driving frequency are observed. A model is proposed to account for the device operation.

Long-lived polarons and triplet excitons in ladder-type poly(p-phenylenes) and poly(p-phenylene ethynylenes)

Recent x-band optically detected magnetic resonance studies of spin 1/2 polaron and spin 1 triplet exciton dynamics in ladder-type poly(p-phenylene) and poly(p-phenylene ethynylene) (PPE) films and solutions are described. The results suggest that the polaron resonance is due to interchain polaron pairs with lifetimes 10 microsecond(s) <EQ (tau) <EQ 4 ms range. The absence of delayed fluorescence at such times as well as other observations lead to the conclusion that the mechanism responsible for this resonance is the nonradiative quenching of singlet excitons by the polarons, whose population decreases at the field-for- resonance. The full-field triplet pattern is 700 - 1200 G wide, consistent with a triplet localized on a phenylene ring. In frozen toluene solutions of PPE, the amplitudes (Delta) I/I of both the polaron and half-field triplet resonances decrease similarly with concentration, and increase similarly with laser power P as P(alpha ), where 1/3 <EQ (alpha) <EQ 1/2. Hence, the triplet resonance is believed to be due to triplet intrinsically trapped and stabilized at similar interchain sites. Possible scenarios which link the processes yielding the resonances are also discussed.