On the generation of holes in organic crystals through photo-excited holes in metal contacts

Gaehrs, H. J.; Willig, F.

doi:10.1016/0009-2614(75)85129-3

Cited by 10 publications

(2 citation statements)

References 18 publications

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“…Bimolecnlar triplet decay seen initially in curve a of Fig. 5 has not been considered in formula (6) and should lead to a somewhat smaller triplet flux than calculated. From Fig.…”

Section: Contact-dependent Hole Generation Through Singlet and Triplementioning

confidence: 89%

“…For an ideal crystal without surface traps only the first process of hole generation should occur. However, the latter mechanism is similar to photon-induced release of holes from surface traps, which causes the long-wavelength photocurrent in the range and below the S,-T, transition in the A t electrolytic contacts (lo-, KCl with about 4 x organic crystal [6]. In view of the very large surplus energy for the electron transfer reaction of the singlet exciton, direct electron transfer should also lead to a n electronically excited doublet state at the crystal surface [29].…”

Section: Discussionmentioning

confidence: 99%

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Contact-Dependent Electron Transfer Quenching of Singlet and Triplet Excitons at the Surface of Organic Crystals

Gaehrs

Willig

1975

Phys. Stat. Sol. (a)

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“…Bimolecnlar triplet decay seen initially in curve a of Fig. 5 has not been considered in formula (6) and should lead to a somewhat smaller triplet flux than calculated. From Fig.…”

Section: Contact-dependent Hole Generation Through Singlet and Triplementioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Contact-Dependent Electron Transfer Quenching of Singlet and Triplet Excitons at the Surface of Organic Crystals

Gaehrs

Willig

1975

Phys. Stat. Sol. (a)

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Plasmonic Internal Photoemission for Accurate Device In Situ Measurement of Metal‐Organic Semiconductor Injection Barriers

Dhanker

Chopra

Giebink

2014

Adv Funct Materials

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4775www.MaterialsViews.com wileyonlinelibrary.com the challenge of independently and reliably measuring key parameters such as the injection energy barrier directly in the device geometries in which currentvoltage ( J -V ) characteristics are measured.Ultraviolet photoelectron spectroscopy (UPS) is arguably the most successful and widely used method for determining energy level alignment at MO interfaces, [8][9][10] however the energetics deduced from this method as well as its inverse counterpart are not in general the same as that in an actual device due to the difference between surface and bulk polarization energies. [ 9,10 ] That is, the energy of a charge carrier near an MO interface is stabilized by polarization and lattice relaxation of the surrounding molecules and the adjacent metal (≈0.5-1 eV), whereas surface-specifi c techniques such as UPS, Kelvin probe and scanning tunneling microscopy all measure the energy of charge carriers at an organic fi lm surface, stabilized only by polarization from the underlying half-space.Internal photoemission (IPE) by contrast is carried out directly in the device of interest (i.e., device in situ) and is well established for measuring the injection barrier at metalinorganic semiconductor contacts. [ 11,12 ] In this approach, the metal contact is illuminated directly with visible/near infrared light below the semiconductor bandgap leading to the excitation of hot carriers in the metal. Those carriers with suffi cient energy and momenta to surmount the injection barrier, B φ , are emitted into the semiconductor resulting in a photocurrent with yield per absorbed photon, Y , according to the Fowler relationship: [ 13 ] where A is a constant that refl ects the strength of the involved optical transitions. Internal photoemission has previously been applied to MO interfaces, [ 14,15 ] however as demonstrated below, interpretation of the data is complicated by the fact that disorder and impurities in organic semiconductors lead to low-level absorption tails extending deep into the optical gap. This sub-gap absorption, together with photo-detrapping transitions within the disorder-broadened highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) transport levels leads to a background photocurrent that is diffi cult to Current injection in organic semiconductors remains diffi cult to predict due in large part to the challenge of characterizing the contact energy barrier and interface density of states directly in organic electronic devices. Here, resonant coupling to surface plasmon polariton modes of a metal contact is demonstrated as a means to carry out internal photoemission (IPE) accurately in disordered organic semiconductor devices and enable direct measurement of the contact injection barrier by isolating true IPE from spurious sub-gap organic photoconductivity. The substantial increase in sensitivity afforded by resonant coupling enables measurement in the low-fi eld injection regime where deviation from the standard Fowler prediction is explained q...

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Exchange of holes between organic crystals and metal films evaporated in high vacuum

Korsch

Willig

Gaehrs

et al. 1976

Phys. Stat. Sol. (a)

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Injection currents in organic crystals have been measured t o determine the rate of hole exchange with metal contacts evaporated in high vacuum. At a gold contact the rate of hole injection increased with decreasing ionisation energy of the organic crystal but was depending on the evaporation procedure due t o an influence of residual gas molecules. The excitation spectrum of the photocurrent agreed with hole generation through triplet excitons. Below the So-S, transition hole generation was due t o surface states in the band gap. Der Anstausch von Defektelektronen zwischen organischen Kristallen und im Hochvakunm aufgedampften Metallkontakten wurde als Injektionsstrom gemessen. Die Defektelektronen-Injektion &us einem Gold-Kontakt nahm mit abnehniender Ionisierungsenergie des organischen Kristalls zu, wobei jedoch eine Abhangigkeit von den Aufdampfbedingungen den EinfluB von Restgasmolekiilen erkennen lieB. Das Anregungsspektrum des Photostroms entsprach einer Defektelektronen-Erzeugung durch Triplett-Exzitonen. Unterhalb dea S, -S, ubergangs geschah die Defektelektronen-Erzeugung iiber Oberflachenzustande. l ) Berlin-Dahlem, Faradayweg 4-6.

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On the generation of holes in organic crystals through photo-excited holes in metal contacts

Cited by 10 publications

References 18 publications

Contact-Dependent Electron Transfer Quenching of Singlet and Triplet Excitons at the Surface of Organic Crystals

Contact-Dependent Electron Transfer Quenching of Singlet and Triplet Excitons at the Surface of Organic Crystals

Plasmonic Internal Photoemission for Accurate Device In Situ Measurement of Metal‐Organic Semiconductor Injection Barriers

Exchange of holes between organic crystals and metal films evaporated in high vacuum

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