Piergiulio Di Marco - Academia.edu (original) (raw)
Papers by Piergiulio Di Marco
Synthet Metal, 1996
Photoconduction in solid films of C69 has been investigated as a function of applied field, excit... more Photoconduction in solid films of C69 has been investigated as a function of applied field, excitation wavelength and light intensity. Exposure of the films to ultraviolet and visible light (200-800 nm), and externally applied voltage produced photocurrent in the range 10-"-10-6 A/ cm'; the magnitude depended on the polarity of the illuminated electrode. This asymmetry is a function of electric field and light penetration depth. It is attributed to a combined effect of varying excitonic electron injection from the Al cathode and a difference in mobility of holes and electrons. Spectral features of the photocurrent vary from sample to sample, but a notable number of recurrent bands can be distinguished, in addition to principal features such as their antibatic behaviour with the absorption spectrum and higher photogeneration yield in the longwavelength part of the spectra above 400 nm. This behaviour can be explained by a vast range of orbitally and spin forbidden electron transitions identified in high-resolution absorption spectra of CsO. Correspondingly, a complex relationship between photocurrent and light intensity is observed.
Synthetic Metals, Jun 30, 1999
The electroluminescent characteristics of OLEDs based on 1,4-bis(pyrrol-2yl)-2,5dicyanobenzene (D... more The electroluminescent characteristics of OLEDs based on 1,4-bis(pyrrol-2yl)-2,5dicyanobenzene (DPDCB), in single (SL) and double layer (DL) configuration are reported. In DL configuration the DPDCB works both as emitter as well as hole transporting layer together with Triphenylamine (TPD) and (Hydroxyquinolinolato)~Al(III) (Alqs) respectively. Luminance of about 1200 cd/m2 was achieved when the DPDCB is used as hole transporting layer (HTL)
Appl Phys Lett, 1998
The temporal behavior of the electroluminescence (EL) from thin-film indium-tin-oxide (ITO)/aroma... more The temporal behavior of the electroluminescence (EL) from thin-film indium-tin-oxide (ITO)/aromatic diamine (TPD)/Al (III) 8-hydroxyquinoline light-emitting diodes (LEDs) upon the application of a rectangular driving voltage is analyzed in terms of the electron-hole ...
Physica Status Solidi B Basic Research, May 1, 1989
Phys Rev B, 2004
The electrophosphorescence (EPH) efficiency was found to increase by up to 6% for the devices bas... more The electrophosphorescence (EPH) efficiency was found to increase by up to 6% for the devices based on a metallo-organic phosphor of iridium and 2% for those based on a metal-organic complex of platinum as an external magnetic field increased to 500 mT. Also, a difference in the field dependence of the EPH for these devices has been observed. We demonstrate that these experimental findings can principally be understood in terms of the Zeeman and hyperfine interactions of electrons located on phosphor molecules and holes located on the hole-transporting molecules, forming correlated electron-hole pairs in the emitting layer. The difference in the field behavior of the effect for the two phosphors results from their different molecular structures.
Http Dx Doi Org 10 1080 08957959008246066, Dec 1, 2006
ABSTRACT
Advanced Materials For Optics and Electronics, 1999
ABSTRACT
Synthetic Metals, 2001
Double layer (DL) electroluminescent devices, made with TPD (75%) in polycarbonate (PC) and with ... more Double layer (DL) electroluminescent devices, made with TPD (75%) in polycarbonate (PC) and with a mixed ligand 8-quinolinolato aluminium chelate as electron transporting and emitting material, show higher electroluminescence (EL) quantum yield (2.2%) and an increased blue EL emission in comparison with Tris±(8-hydroxyquinolinate)Al(III) (Alq 3). The solid state photoluminescence (PL) quantum yield is as high as 60%, about ®ve-fold the Alq 3 value. In spite of the high PL yield, EL ef®ciency is not as much high; this can be attributed to a strong electron mobility dependence on the electric ®eld, which contributes to a slower increase with the ®eld of the EL quantum yield.
Metal/Nonmetal Microsystems: Physics, Technology, and Applications, 1996
ABSTRACT Optical and electrical characteristics of single- and double-layer organic electrolumine... more ABSTRACT Optical and electrical characteristics of single- and double-layer organic electroluminescent (EL) diodes based on commonly used low-molecular weight materials of an aromatic diamine (TPD) and 8-hydroxyquinoline aluminum complex (Alq3) were investigated in order to compare their operation mechanisms.
Molecular Crystals and Liquid Crystals, 1985
Polyorganophosphazenes are electrical insulators and in general non photoconducting polymers. The... more Polyorganophosphazenes are electrical insulators and in general non photoconducting polymers. The doping with trinitrofluo-renone changes their optical and electrical characteristics: new optical absorption bands appear in the visible region and the doped polymers show photoconductive properties. The photoresponse seems to be related to the nature of the organic group attached to the polymer chain.
MRS Proceedings, 1999
ABSTRACTObservation of electroluminescence (EL) in single layer of molecularly doped polymer (MDP... more ABSTRACTObservation of electroluminescence (EL) in single layer of molecularly doped polymer (MDP) films is reported. The EL diodes constructed by spin coating technique contain Bisphenol-A-polycarbonate (PC), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and 2-(4-biphenyl)-5-(4-terbutylphenyl)1,3,4-oxadiazole (PBD) with the configuration: ITO/PC(20%):TPD(40%):PBD(40%)/Ca, Ag. The EL emission ranges in the green-yellow part of the spectrum and is red shifted respect to the photolu minescence (PL) both of PC:TPD and of PC:PBD. It can be assigned to emission from an exciplex state resulting from the interaction between TPD and PBD, as confirmed by stationary and pulsed fluorescence spectroscopy, and also from other states (triplets, traps or ‘electoplexes’) emitting at lower energies.
Molecular Crystals and Liquid Crystals, 1975
The hole mobility in dibenzothiophene, perpendicular to the ab plane of the crystal, was observed... more The hole mobility in dibenzothiophene, perpendicular to the ab plane of the crystal, was observed using time-of-flight measurements to be 1.6 cm V cm at 295 K. The mobility varies as T in the range of temperatures comprised between 295 K and 360 K.
Thin Solid Films, 1979
... Printed in the Netherlands 91 PHOTOEMISSION OF ELECTRONS FROM METAL ELECTRODES INTO POLY-N-VI... more ... Printed in the Netherlands 91 PHOTOEMISSION OF ELECTRONS FROM METAL ELECTRODES INTO POLY-N-VINYLCARBAZOLE GABRIELE GIRO AND ... In the field of organic compounds,Dresner and Williams' have observed the photoemission of holes from metal ...
Synthetic Metals, 1996
Two types of electroluminescence (EL), injection-controlled (IC) with T,,> T=, and volume-control... more Two types of electroluminescence (EL), injection-controlled (IC) with T,,> T=, and volume-controlled (VC) with ;T~ < TV, in organic light-emitting diodes (LEDs) are discussed using the notions of recombination (T& and transit (TV) times of charge carriers. The results of experimental and theoretical studies presented show that the EL intensity (QEp,,) is, in general, a nonlinear function of the current density (j) in an EL diode. Often it can be approximated by a power-type function @EL ajn, with the power, n, dependent on LED structure, the nature of light-emitting material, injection and transport mechanisms of the charge carriers. In the LEDs with carrier mobilities independent of electric field 12 n < 2 for both ICEL and VCEL operation modes. In the ICEL, n = 1+ w,/w,, where w1 and o2 are quantities characterizing various charge injection mechanisms into the EL sample. Field-dependent mobility and charge carrier trapping lead @EL to be a sublinear or supralinear function of j. Selected examples of experimental &(j) relationships on single-layer ITO/Alq,/Mg/Ag (%hydroxyquinoline aluminium complex, Alq,), double-layer ITO/TPD/Alq,/Mg/Ag (aromatic diamine, TPD), ITO/QAC/Alq,/Mg/Ag (quinacridone, QAC) , and triple-layer ITO/QAC/Alq,/PBP/Mg/Ag (perylene bisimide pigment, PBP) are presented briefly to illustrate various types of operation modes of organic LEDs.
Synthet Metal, 1996
Photoconduction in solid films of C69 has been investigated as a function of applied field, excit... more Photoconduction in solid films of C69 has been investigated as a function of applied field, excitation wavelength and light intensity. Exposure of the films to ultraviolet and visible light (200-800 nm), and externally applied voltage produced photocurrent in the range 10-"-10-6 A/ cm'; the magnitude depended on the polarity of the illuminated electrode. This asymmetry is a function of electric field and light penetration depth. It is attributed to a combined effect of varying excitonic electron injection from the Al cathode and a difference in mobility of holes and electrons. Spectral features of the photocurrent vary from sample to sample, but a notable number of recurrent bands can be distinguished, in addition to principal features such as their antibatic behaviour with the absorption spectrum and higher photogeneration yield in the longwavelength part of the spectra above 400 nm. This behaviour can be explained by a vast range of orbitally and spin forbidden electron transitions identified in high-resolution absorption spectra of CsO. Correspondingly, a complex relationship between photocurrent and light intensity is observed.
Synthetic Metals, Jun 30, 1999
The electroluminescent characteristics of OLEDs based on 1,4-bis(pyrrol-2yl)-2,5dicyanobenzene (D... more The electroluminescent characteristics of OLEDs based on 1,4-bis(pyrrol-2yl)-2,5dicyanobenzene (DPDCB), in single (SL) and double layer (DL) configuration are reported. In DL configuration the DPDCB works both as emitter as well as hole transporting layer together with Triphenylamine (TPD) and (Hydroxyquinolinolato)~Al(III) (Alqs) respectively. Luminance of about 1200 cd/m2 was achieved when the DPDCB is used as hole transporting layer (HTL)
Appl Phys Lett, 1998
The temporal behavior of the electroluminescence (EL) from thin-film indium-tin-oxide (ITO)/aroma... more The temporal behavior of the electroluminescence (EL) from thin-film indium-tin-oxide (ITO)/aromatic diamine (TPD)/Al (III) 8-hydroxyquinoline light-emitting diodes (LEDs) upon the application of a rectangular driving voltage is analyzed in terms of the electron-hole ...
Physica Status Solidi B Basic Research, May 1, 1989
Phys Rev B, 2004
The electrophosphorescence (EPH) efficiency was found to increase by up to 6% for the devices bas... more The electrophosphorescence (EPH) efficiency was found to increase by up to 6% for the devices based on a metallo-organic phosphor of iridium and 2% for those based on a metal-organic complex of platinum as an external magnetic field increased to 500 mT. Also, a difference in the field dependence of the EPH for these devices has been observed. We demonstrate that these experimental findings can principally be understood in terms of the Zeeman and hyperfine interactions of electrons located on phosphor molecules and holes located on the hole-transporting molecules, forming correlated electron-hole pairs in the emitting layer. The difference in the field behavior of the effect for the two phosphors results from their different molecular structures.
Http Dx Doi Org 10 1080 08957959008246066, Dec 1, 2006
ABSTRACT
Advanced Materials For Optics and Electronics, 1999
ABSTRACT
Synthetic Metals, 2001
Double layer (DL) electroluminescent devices, made with TPD (75%) in polycarbonate (PC) and with ... more Double layer (DL) electroluminescent devices, made with TPD (75%) in polycarbonate (PC) and with a mixed ligand 8-quinolinolato aluminium chelate as electron transporting and emitting material, show higher electroluminescence (EL) quantum yield (2.2%) and an increased blue EL emission in comparison with Tris±(8-hydroxyquinolinate)Al(III) (Alq 3). The solid state photoluminescence (PL) quantum yield is as high as 60%, about ®ve-fold the Alq 3 value. In spite of the high PL yield, EL ef®ciency is not as much high; this can be attributed to a strong electron mobility dependence on the electric ®eld, which contributes to a slower increase with the ®eld of the EL quantum yield.
Metal/Nonmetal Microsystems: Physics, Technology, and Applications, 1996
ABSTRACT Optical and electrical characteristics of single- and double-layer organic electrolumine... more ABSTRACT Optical and electrical characteristics of single- and double-layer organic electroluminescent (EL) diodes based on commonly used low-molecular weight materials of an aromatic diamine (TPD) and 8-hydroxyquinoline aluminum complex (Alq3) were investigated in order to compare their operation mechanisms.
Molecular Crystals and Liquid Crystals, 1985
Polyorganophosphazenes are electrical insulators and in general non photoconducting polymers. The... more Polyorganophosphazenes are electrical insulators and in general non photoconducting polymers. The doping with trinitrofluo-renone changes their optical and electrical characteristics: new optical absorption bands appear in the visible region and the doped polymers show photoconductive properties. The photoresponse seems to be related to the nature of the organic group attached to the polymer chain.
MRS Proceedings, 1999
ABSTRACTObservation of electroluminescence (EL) in single layer of molecularly doped polymer (MDP... more ABSTRACTObservation of electroluminescence (EL) in single layer of molecularly doped polymer (MDP) films is reported. The EL diodes constructed by spin coating technique contain Bisphenol-A-polycarbonate (PC), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and 2-(4-biphenyl)-5-(4-terbutylphenyl)1,3,4-oxadiazole (PBD) with the configuration: ITO/PC(20%):TPD(40%):PBD(40%)/Ca, Ag. The EL emission ranges in the green-yellow part of the spectrum and is red shifted respect to the photolu minescence (PL) both of PC:TPD and of PC:PBD. It can be assigned to emission from an exciplex state resulting from the interaction between TPD and PBD, as confirmed by stationary and pulsed fluorescence spectroscopy, and also from other states (triplets, traps or ‘electoplexes’) emitting at lower energies.
Molecular Crystals and Liquid Crystals, 1975
The hole mobility in dibenzothiophene, perpendicular to the ab plane of the crystal, was observed... more The hole mobility in dibenzothiophene, perpendicular to the ab plane of the crystal, was observed using time-of-flight measurements to be 1.6 cm V cm at 295 K. The mobility varies as T in the range of temperatures comprised between 295 K and 360 K.
Thin Solid Films, 1979
... Printed in the Netherlands 91 PHOTOEMISSION OF ELECTRONS FROM METAL ELECTRODES INTO POLY-N-VI... more ... Printed in the Netherlands 91 PHOTOEMISSION OF ELECTRONS FROM METAL ELECTRODES INTO POLY-N-VINYLCARBAZOLE GABRIELE GIRO AND ... In the field of organic compounds,Dresner and Williams' have observed the photoemission of holes from metal ...
Synthetic Metals, 1996
Two types of electroluminescence (EL), injection-controlled (IC) with T,,> T=, and volume-control... more Two types of electroluminescence (EL), injection-controlled (IC) with T,,> T=, and volume-controlled (VC) with ;T~ < TV, in organic light-emitting diodes (LEDs) are discussed using the notions of recombination (T& and transit (TV) times of charge carriers. The results of experimental and theoretical studies presented show that the EL intensity (QEp,,) is, in general, a nonlinear function of the current density (j) in an EL diode. Often it can be approximated by a power-type function @EL ajn, with the power, n, dependent on LED structure, the nature of light-emitting material, injection and transport mechanisms of the charge carriers. In the LEDs with carrier mobilities independent of electric field 12 n < 2 for both ICEL and VCEL operation modes. In the ICEL, n = 1+ w,/w,, where w1 and o2 are quantities characterizing various charge injection mechanisms into the EL sample. Field-dependent mobility and charge carrier trapping lead @EL to be a sublinear or supralinear function of j. Selected examples of experimental &(j) relationships on single-layer ITO/Alq,/Mg/Ag (%hydroxyquinoline aluminium complex, Alq,), double-layer ITO/TPD/Alq,/Mg/Ag (aromatic diamine, TPD), ITO/QAC/Alq,/Mg/Ag (quinacridone, QAC) , and triple-layer ITO/QAC/Alq,/PBP/Mg/Ag (perylene bisimide pigment, PBP) are presented briefly to illustrate various types of operation modes of organic LEDs.