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We apply percolation theory to explain the operation of multiple-use gas sensors based on organic field effect transistors (OFETs). For reversible operation, we predict that energetic disorder in the channel can obscure interactions with the analyte, because chemically induced traps are overwhelmed by the natural disorder. Consequently, the sensitivity of an energetically disordered OFET-based chemical sensor is significantly inferior to the ideal disorder-free case. Current modulation in disordered OFETs is predicted to rely on morphological alteration of percolation paths. The theory is compared to results from an array of metal phthalocyanine (MPC) transistors exposed to low concentrations of solvents. Despite the presence of very large adsorption fractions of solvent on the channel, the current modulation is small, consistent with theory. Chemical selectivity is possible, however, because the central metal atom of the MPC determines the strength of the solvent--MPC interaction, which in turn determines the amount of solvent adsorbed on the OFET channel. This work suggests that OFET-based sensors may be better suited to applications where the analyte binding energy exceeds the intrinsic energetic disorder of the organic semiconductor.

A fluorescent dye can improve the efficiency of electroluminescent organic light-emitting devices. High efficiency energy transfer from singlet and triplet states is reported in a material doped with phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (II) (PtOEP). Saturated red emission was generated with peak external and internal quantum efficiencies of 4% and 23%.

Discusses the use of a phosphorescent sensitizer to obtain the maximum luminous efficiency from a fluorescent dye. Mechanism for energetic coupling between phosphorescent and fluorescent molecular species as a long-range, non-radiative energy transfer; Use of the approach to nearly quadruple the efficiency of a fluorescent red organic light-emitting device.

We describe the performance of an organic light-emitting device employing the greenelectrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)[sub3]] doped into a 4,4'-N,N'-dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m[sup2] , the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to Ir(ppy)[sub3] , leading to a high internal efficiency. In addition, the short phosphorescent decay time of Ir(ppy)[sub3] (<1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m[sup2]. [ABSTRACT FROM AUTHOR]

Reports that external quantum efficiencies of up to (5.6+/-0.1)% at low brightness and (2.2+/-0.1)% at 100 cd/m[sup 2] were obtained from a red electrophosphorescent device containing the dye 2,3,7,8,12,13,17,19-octaethyl-21H23H-phorpine platinum(II) (PtOEP) doped in a 4,4',N,N'-dicarbazole-biphenyl host. Photoluminescent efficient of PtOEP; Efficiency loses due to nonradiative recombination.

Demonstrates the use of low pressure organic vapor phase deposition (LP-OVPD) to fabricate organic light emitting devices (OLED) based on organic thin films. Characteristics of the light emitting devices; Comparison of the heterojunction OLED with the thermally evaporated-OLED; Percentage of the quantum efficiency of LP-OVPD grown device.