Excitonic singlet-triplet ratios in molecular and polymeric organic materials

A simple technique employing reverse bias measurements of photoluminescent efficiency is described to determine the excitonic singlet-triplet formation statistics of electroluminescent organic thin films. Using this method, the singlet fractions in thin films of two organic emissive materials commonly used in organic light emitting devices, tris(8-hydroxyquinoline) aluminum (Alq 3 ) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), are found to be (20′1)% and (20′4)%, respectively. Results are confirmed using a sensitive synchronous detection scheme. We discuss other measurements and the current understanding of exciton formation statistics in polymeric and small molecular weight organic electroluminescent materials.

[1]  G. Hadziioannou,et al.  Polymers for opto-electronic applications: structure and morphology of thin films and their interfaces , 2001 .

[2]  M. I. Khan,et al.  Evidence for electric field-assisted dissociation of the excited singlet state into charge carriers in MEH–PPV , 1998 .

[3]  Stephen R. Forrest,et al.  Weak microcavity effects in organic light-emitting devices , 1998 .

[4]  Shuai,et al.  Singlet and triplet exciton formation rates in conjugated polymer light-emitting diodes , 2000, Physical review letters.

[5]  Stephen R. Forrest,et al.  Very-high-efficiency double-heterostructure copper phthalocyanine/C60 photovoltaic cells , 2001 .

[6]  J. Brédas,et al.  On the luminescence efficiency of polymer light-emitting diodes: a quantum-chemical investigation , 2001 .

[7]  S. Forrest,et al.  Highly efficient phosphorescent emission from organic electroluminescent devices , 1998, Nature.

[8]  D. K. Schwartz,et al.  Dynamic scaling of the submonolayer island size distribution during self-assembled monolayer growth , 1999 .

[9]  T. Főrster,et al.  10th Spiers Memorial Lecture. Transfer mechanisms of electronic excitation , 1959 .

[10]  Stephen R. Forrest,et al.  Phosphorescent materials for application to organic light emitting devices , 1999 .

[11]  W. R. Salaneck,et al.  Electroluminescence in conjugated polymers , 1999, Nature.

[12]  Shizuo Tokito,et al.  Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer , 2001 .

[13]  F. E. Karasz,et al.  Polaron-pair generation in poly(phenylene vinylenes). , 1992, Physical review. B, Condensed matter.

[14]  Richard H. Friend,et al.  Electroluminescence emission pattern of organic light-emitting diodes: Implications for device efficiency calculations , 2000 .

[15]  Stephen R. Forrest,et al.  Interface-limited injection in amorphous organic semiconductors , 2001 .

[16]  L. J. Hartwell,et al.  Triplet energies of pi-conjugated polymers. , 2001, Physical review letters.

[17]  Stephen R. Forrest,et al.  EXCITONIC SINGLET-TRIPLET RATIO IN A SEMICONDUCTING ORGANIC THIN FILM , 1999 .

[18]  Donal D. C. Bradley,et al.  High brightness and efficiency blue light-emitting polymer diodes , 1998 .

[19]  A. S. Dhoot,et al.  Spin-dependent exciton formation in π-conjugated compounds , 2001, Nature.

[20]  S. R. Forrest,et al.  High-efficiency fluorescent organic light-emitting devices using a phosphorescent sensitizer , 2000, Nature.

[21]  R. Friend,et al.  The energy gap law for triplet states in Pt-containing conjugated polymers and monomers. , 2001, Journal of the American Chemical Society.

[22]  David Beljonne,et al.  Triplet formation and decay in conjugated polymer devices , 2002 .

[23]  Conjugation-length dependence of spin-dependent exciton formation rates in pi-conjugated oligomers and polymers. , 2001, Physical review letters.

[24]  Stephen R. Forrest,et al.  Relationship between electroluminescence and current transport in organic heterojunction light‐emitting devices , 1996 .

[25]  Ifor D. W. Samuel,et al.  Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers , 1995 .

[26]  Z. Vardeny,et al.  Photophysics properties of blue-emitting polymers , 2001 .

[27]  D. McClure,et al.  Spin‐Orbit Interaction in Aromatic Molecules , 1952 .

[28]  Yong Cao,et al.  Improved quantum efficiency for electroluminescence in semiconducting polymers , 1999, Nature.

[29]  R. Friend,et al.  Donor-acceptor interactions in organometallic and organic poly-ynes , 1999 .

[30]  S. Ramasesha,et al.  Formation cross-sections of singlet and triplet excitons in π-conjugated polymers , 2001, Nature.

[31]  Lu,et al.  Optically detected magnetic resonance study of efficient two-layer conjugated polymer light-emitting diodes. , 1996, Physical review. B, Condensed matter.

[32]  W. Stampor,et al.  Electric field effect on luminescence efficiency in 8-hydroxyquinoline aluminum (Alq3) thin films , 1997 .

[33]  Stephen R. Forrest,et al.  High-efficiency yellow double-doped organic light-emitting devices based on phosphor-sensitized fluorescence , 2001 .

[34]  Charles D. Merritt,et al.  Photoluminescence quantum yield of pure and molecularly doped organic solid films , 1999 .

[35]  A. S. Dhoot,et al.  Triplet Formation In Polyfluorene Devices , 2002 .

[36]  Richard H. Friend,et al.  Factors Influencing Stimulated Emission from Poly( p-phenylenevinylene) , 1997 .

[37]  S. Forrest,et al.  Nearly 100% internal phosphorescence efficiency in an organic light emitting device , 2001 .

[38]  Stephen R. Forrest,et al.  Photoluminescence efficiency and absorption of aluminum-tris-quinolate (Alq3) thin films , 1996 .

[39]  S. Horng,et al.  Triplet-to-singlet exciton formation in poly(p-phenylene-vinylene) light-emitting diodes. , 2003, Physical review letters.

[40]  S. Ramasesha,et al.  Electron correlation effects in electron-hole recombination in organic light-emitting diodes , 2003 .

[41]  Kurtz,et al.  Photocarrier generation and transport in sigma -bonded polysilanes. , 1987, Physical review. B, Condensed matter.

[42]  Antoine Kahn,et al.  Organic semiconductor heterointerfaces containing bathocuproine , 1999 .

[43]  Stephen R. Forrest,et al.  Prospects for electrically pumped organic lasers , 2002 .

[44]  Yongmin Liang,et al.  High-efficiency red-light emission from polyfluorenes grafted with cyclometalated iridium complexes and charge transport moiety. , 2003, Journal of the American Chemical Society.

[45]  Harrison,et al.  Singlet Intrachain Exciton Generation and Decay in Poly (p-phenylenevinylene). , 1996, Physical review letters.