Hot Carrier Injection into Molecular Crystals and Its Relevance to the Field Dependence of Photocurrents

Baessler, H.; Killesreiter, H.

doi:10.1002/pssb.2220530119

Cited by 27 publications

(8 citation statements)

References 19 publications

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“…10 A Ê results. This value is comparable with that in crystalline anthracene (Baessler and Killesreiter 1972). Although the classical and quantum mechanical approach can be used to rationalize current± voltage± luminance characteristics in organic EL devices, there is a need for future work to establish a criterion for their applicability.…”

Section: Brightness-device Current Relationshipsupporting

confidence: 50%

Operation mechanisms of thin film organic electroluminescent diodes

Kalinowski¹,

Camaioni²,

Marco³

et al. 1996

International Journal of Electronics

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Optical and electrical characteristics of single-and double-layer (DL) organic electroluminescent diodes based on an aromatic diamine (TPD) and 8-hydroxyquinoline aluminium complex (Alq3) were investigated to compare their operation mechanisms. From the optical spectra of thin films and of single-layer (SL) and DL devices, the nature of emitting states is revealed and their energy level scheme is derived. The injection-controlled electroluminescence mode of the operation of SL and DL devices provides a powerful experimental approach for investigating the process of charge injection. It is demonstrated that the physical mechanism responsible for charge injection is the primary carrier penetration over the image force barrier at high electric fields, and field-assisted thermionic injection in the low-field regime of operation of these devices. The role of material and device structure for charge injection parameters is pointed out in this context.

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Section: Brightness-device Current Relationshipsupporting

confidence: 50%

Operation mechanisms of thin film organic electroluminescent diodes

Kalinowski¹,

Camaioni²,

Marco³

et al. 1996

International Journal of Electronics

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“…(1) and (3) and, concomitantly, of the above assumptions will be checked using literature data on intrinsic photoconduction in crystalline anthracene.…”

Section: Comparison With Experimental Resultsmentioning

confidence: 99%

“…Then electron and hole will in total suffer n = AE/E, scattering events. If the scattering mean free-path is 1, the carriers get thermalized a t an average mutual distance@) r t h =lo(n/3)112 =lo(AE/3E,)1/2 (1) If r l h <e2/ekT, a thermalized carrier pair is still under the influence of attractive coulombic forces, the binding energy being…”

Section: B a N D G A P -D E T E R M I N A T I O N T H R O U G H A U Tmentioning

confidence: 99%

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Bandgap-Determination from Autoionization Data in Molecular Crystals

Baessler

Killesreiter

1973

Molecular Crystals and Liquid Crystals

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An interpretation of action spectra for intrinsic photo-conduction in crystalline anthracene and tetracene is presented. It is shown (i) that the primary dissociation probability of a molecular excited state does not depend on photon energy as long as its energy exceeds the energy of the chargetransfer state and (ii) that excess energy of the excited state is dissipated during thermalization of the generated electron-hole pair in course of a randomwalk process. The energy balance for the complete autoionization process allows precise determination of the band-gap. The values E , = 4.00 &0.02 for anthracene and E , = 3.11 1 0 . 0 3 eV for tetracene are obtained.

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“…By definition this energy does not depend on the injection mechanism and, therefore, its value at a given field should be characteristic of the near-contact crystal defects which might be similar in van der Waals-type crystals. Indeed, the value AE = (0.20 0.05) eV (at F = lo4 V/cm) has been also obtained for electrons injected by photons from a cerium or sodium contact into anthracene [24]. With AE = 0.15 eV the fraction of effectively dissociating excitons, expressed by q = exp (-A E / k T ) , amounts to 2.5 x at room temperature.…”

Section: Interpretation and Discussion Of Resultsmentioning

confidence: 95%

Energy‐Dependent Excitonic Injection of Charge into Anthracene Crystals

Strzelecka

Godlewski

Kalinowski

1992

Physica Status Solidi (b)

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Steady-state exciton-injection currents (EIC) as a function of electric field and temperature are measured in anthracene crystals upon energy-selective excitation within the So + S, transition. The current for each given absorption coefficient decreases as the excitation energy (ho) passes through the high-energy wing and is swept downward the low-energy wing (Urbach tail) of the absorption band, demonstrating that the flux of excitons reaching the injecting contact is energy dependent. The maximum absorption at the So + S, 0-0 transition establishes a demarcation energy ha,. Above hw, only diffusion of mobile (band) excitons (S) is an injection-determining process, below faw, thermal activation of localized states (SJ becomes an unavoidable step in the S-exciton creation process, diminishing the effective flux of S-excitons reaching the contact. An analysis of the dependence of the activation energy on the localization energy hw, -hm of primarily excited S, states indicates that EIC are the sum of a singlet exciton-injection contribution and a triplet exciton-injection contribution, the triplets being produced via intersystem crossing transitions from S and S, states. A theoretical description of excitonic processes underlying charge injection is presented and applied to the experimental results. Agreement between theoretical predictions and experiment is good if the frequency factor for the thermally activated S , -+ S excitation is assumed to be z lo9 s -'.Stationare Exzitoneninjektionsstrome (EIC) werden in Abhangigkeit vom e1ektri:chen Feld und der Ternperatur in Anthrazenkristallen unter energieselektiver Anregung im So .+ S,-Ubergang gemessen. Fur jeden vorgegebenen Absorptionskoeffizienten nimmt der Strom ab, wenn die .Anregungsenergie ho im hochenergetischen oder im niederenergetischen (Urbach-Auslauier) Fliigel des Absorptionsbandes liegt, was zeigt, dalj der den injizierenden Kontakt erreichende Exzitonenflu5 energieabhangig ist. Das Absorptionsmaximum am 0-0 So -+ S,-ubergang legt eine Energiemarkierung hoo fest. Oberhalb hw, bestimmt nur die Diffusion beweglicher (Band)-Exzitonen S den Injektionsprozelj, unterhalb hw, ist thermische Aktivierung von lokalisierten Zustanden S, ein unausweichlicher Schritt im Prozelj der S-Elektronenbildung, wodurch der effektive Flu13 der den Kontakt erreichenden S-Exzitonen verringert wird. Eine Analyse der Abhangigkeit der Aktivierungsenergie von der Lokalisierungsenergie hwo -hw der primar angeregten S,-Zustande zeigt, dalj die EIC sich aus einem Singulett-und einem Triplett-Exzitoninjektionsanteil zusammensetzen, dabei entstehen die Triplets durch Intersystem-Crossing aus S und S,-Zustlnden. Die der Ladungsinjektion zugrundeliegenden Exzitonenprozesse werden theoretisch beschrieben und auf experimentelle Ergebnisse bezogen. Die obereinstimmung von Theorie und Experiment ist gut, wenn der Frequenzfaktor fur die thermisch aktivierte S, + S-Anregung zu z lo9 s -l angenommen wird.

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Hot Carrier Injection into Molecular Crystals and Its Relevance to the Field Dependence of Photocurrents

Cited by 27 publications

References 19 publications

Operation mechanisms of thin film organic electroluminescent diodes

Operation mechanisms of thin film organic electroluminescent diodes

Bandgap-Determination from Autoionization Data in Molecular Crystals

Energy‐Dependent Excitonic Injection of Charge into Anthracene Crystals

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