Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C<sub>60</sub>) interface and mobility improvement

Park, Byoungnam; Park, Jonghoo

doi:10.1002/pssr.201308111

Cited by 6 publications

(3 citation statements)

References 34 publications

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“…Oligothiophenes (oT), polythiophene (nT), and their derivatives are conjugated molecular systems that exhibit narrow and tunable optical band gaps and high conductivity. − Because of these outstanding molecular properties, they have been widely used as functional materials in organic electronic devices such as field-effect transistors, − organic light-emitting diodes, , organic photovoltaic devices (OPVs), , and bioelectronics. , As a derivative of nT, poly(3-hexylthiophene-2,5-diyl) (P3HT) is a widely used donor material blended with phenyl-C 61 -butyric acid methyl ester in bulk heterojunction (BHJ) OPVs. , As a small molecule alternative to polymer-based BHJs, sexithiophene (6T)-based BHJs are considered to be more structurally tunable. − Due to shallow (i.e., not far in energy below the vacuum level) highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, oTs and nTs are most commonly used as electron donors in organic electronic devices. Previous studies have shown that multiple oxidation states are accessible for the oligothiophenes and their derivatives via electrochemical , and chemical oxidation; however, there have been no instances of oT reduction chemistry reported to date.…”

Section: Introductionmentioning

confidence: 99%

Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Sang

Pemberton

2019

J. Phys. Chem. C

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Interfacial chemistry of thiophene-based polymers and oligomers in contact with low work function metals is of interest for organic electronic devices. Herein, interfacial reactions of the model thiophene-based oligomer, α-sexithiophene (α-6T), in ultrathin (5 ML) films with vapor-deposited Ag, Al, Mg, and Ca are investigated using surface Raman spectroscopy and X-ray photoelectron spectroscopy under ultrahigh vacuum conditions. Although typically considered an electron donor, results indicate that α-6T is reduced by Al and Ca. The reduction product with Al is the tetrahydrothiophene, whereas complete degradation of the thiophene cores occurs with Ca with the formation of calcium sulfide. In contrast, for the higher work function Ag, contact doping from α-6T to Ag nanoparticles is observed, inducing the formation of polaron states at the interface. Inter-ring torsion by the C–C bond rotation is also induced by electron sharing between α-6T and Ag. Mg, which is expected to undergo electron transfer in a manner similar to Ca based on the work function, instead diffuses through these 5 ML films and deposits on or alloys with the Ag substrate beneath; however, electron transfer from Mg to α-6T is observed in thicker α-6T films suggesting that nucleation into structures with electronic characteristics that resemble those of bulk Mg metal occurs. Overall, the evolution of α-6T interfaces with these low work function metals alters the interfacial energetics through the formation of “gap” states, which ultimately impact the device performance.

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Section: Introductionmentioning

confidence: 99%

Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Sang

Pemberton

2019

J. Phys. Chem. C

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“…While this assumption is almost certainly true for the studies at 120 K, it may be less true at room temperature. However, this is an assumption that has been commonly made for deposition of similarly reactive metals on OT and P3HT films in past work; − ,,− , therefore, we use it here. QCM-reported mass thicknesses for the metals were converted into equivalent metal monolayers using the approach reported by Bebensee , using proper metal lattice constants ( a Ag = 0.40853 nm, a Mg = 0.32094 nm, a Al = 0.40495 nm, a Ca = 0.35884 nm) assuming the close-packed (111) structure for the FCC metals Ag, Al, and Ca and the (0001) structure for the HCP metal Mg. Metal coverages are reported throughout in terms of equivalent monolayers.…”

Section: Experimental Sectionmentioning

confidence: 99%

“…Following our recent spectroscopic studies of metal–organic interfacial molecular processes between Ag, Al, Mg, and Ca and oligothiophenes, including 2,2′:5′,2″-terthiophene (α-3T) and α-sexithiophene (α-6T), this work describes estimation of both the penetration depth of different metals as well as the impact depth of the reaction chemistry of these oliogthiophenes (OTs) using spectroscopic methods. These two oligothiophenes have very similar spectroscopic and materials properties and both are well-accepted as models for polythiophene-based active layer materials. − Here, Raman spectroscopy is combined with depth sensitive, angle-dependent X-ray photoelectron spectroscopy (XPS) to explore OT reduction chemistry as a function of metal coverage.…”

Section: Introductionmentioning

confidence: 99%

Penetration and Reaction Depths of Vapor Deposited Ag, Mg, Al, and Ca on Oligothiophene Thin Films

Sang

Pemberton

2019

Chem. Mater.

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Physical vapor deposition of metal contacts onto thin film organic functional materials is widely used in organic electronic technologies. Using the oligothiophenes (OTs) α-sexithiophene (α-6T) and 2,2′:5′2″-terthiophene (3T) as models for thiophene-containing functional organic films, the metal/organic interface chemistry, metal penetration and reaction depths, and surface metallization processes are investigated and compared for Ag, Al, Mg, and Ca contacts using Raman and X-ray photoelectron spectroscopies. Ag shows only modest penetration, with some surface metallization but no reaction chemistry on OTs. Al and Ca induce some OTs reaction but exhibit the least propensity to penetrate these films with the greatest ability to metallize on the surface. In contrast, Mg exhibits complete penetration of 5 ML OT films with no reaction chemistry or surface metallization. On 50 ML OT films, however, Mg still exhibits the greatest depth of penetration with no surface metallization but does induce a small amount of reaction chemistry initiated by electron transfer from Mg to the OT film. These results reveal significant differences in the depth to which the deposited metal chemically impacts OT thin films during physical vapor deposition and reinforce the critical role of interface chemistry on the performance of organic electronic devices formed with such materials.

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Organic Spin Valves: A Review

Devkota

Geng

Subedi

et al. 2016

Adv Funct Materials

108

106

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accelerated impressively and advanced to a range of materials and a number of techniques to verify the successful injection and transport of the SP carriers. [ 1,2,10,11 ] The effect has been realized in a variety of materials combinations such as FM fi lms, FM/anti-FM coupled layers, or FM semiconductors as the injection/detection electrodes and the metals, superconductors, inorganic semiconductors, organic semiconductors, and insulators including ferroelectric and topological insulators as the spacers. [ 1,2,[12][13][14][15][16][17][18] The GMR effect was extensively studied using non-magnetic metallic interlayer and its applications such as electric switching, magnetic recording, and sensors were suggested and employed. [ 1,2,16 ] However, all-metallic spintronic devices imposed restrictions in applications as they are characterized by short spin relaxation time (≈picosecond) and are not suitable for coherent spin manipulation. [ 1,2,19 ] To overcome these limitations, the spintronics community caught its attention towards hybrid devices with semiconductors (SCs) sandwiched in between the FM layers and continued advancing to a range of semiconducting materials. [ 2,14,[20][21][22] The organic semiconductors (OSCs) are among the youngest members of the spacer materials and were fi rst tested in the spintronic devices only about a decade ago. Nevertheless, OSC devices have been of continuously advancing research topics over the past three decades for their rich physics, fl exible chemi stry, cost effi ciency, and potential applications in new generations of electronic devices including organic light emitting diodes (OLEDs), [23][24][25] organic solar cells, [ 26,27 ] and organic fi eld effect transistor. [ 28,29 ] In fact, OLEDs have already revolutionized the modern display industry and spin-dependent devices such as organic spin valves (OSVs), OLED-based magnetic sensors, and spin-OLEDs are under intensive study to achieve their new avenues. [30][31][32] This increasing interest on organic electronics is for their several distinctions over inorganic counterparts. [19][20][21]33,34 ] Electronically, the band theory explains the electric transport in inorganic SCs while charge hopping is the main transport mechanism in the OSCs with much smaller carrier mobility. This is a favorable condition for large electron-hole pair recombination without the need of using a p-n junction structure. [23][24][25] Spintronically, the inorganic SCs contain heavy atoms giving rise to a large spin-orbit coupling (SOC), which is a response of the electron spin degree of freedom to its orbital environment. The strength of the SOC in solids depends upon the nature of orbital wave functions of electrons and the materials structure. [ 35 ] In case of hydrogenic wave-function-like electrons (s-orbital electrons), it is Organic spintronics is an emerging and potential platform for future electronic devices. Signifi cant progress has been made in understanding the spin injection, manipulation, and detection in organic spin valves in the p...

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Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C₆₀) interface and mobility improvement

Cited by 6 publications

References 34 publications

Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Penetration and Reaction Depths of Vapor Deposited Ag, Mg, Al, and Ca on Oligothiophene Thin Films

Organic Spin Valves: A Review

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Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C60) interface and mobility improvement

Cited by 6 publications

References 34 publications

Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Chemistry at the Interface of α-Sexithiophene and Vapor-Deposited Ag, Al, Mg, and Ca: A Molecular View

Penetration and Reaction Depths of Vapor Deposited Ag, Mg, Al, and Ca on Oligothiophene Thin Films

Organic Spin Valves: A Review

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Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C₆₀) interface and mobility improvement