Soft Nondamaging Contacts Formed from Eutectic Ga-In for the Accurate Determination of Dielectric Constants of Organic Materials

A method for accurately measuring the relative dielectric constant (εr) of thin films of soft, organic materials is described. The effects of the bombardment of these materials with hot Al atoms, the most commonly used top electrode, are mitigated by using electrodes fabricated from eutectic gallium-indium (EGaIn). The geometry of the electrode is defined by injection into microchannels to form stable structures that are nondamaging and that conform to the topology of the organic thin film. The εr of a series of references and new organic materials, polymers, and fullerene derivatives was derived from impedance spectroscopy measurements for both Al and EGaIn electrodes showing the specific limitations of Al with soft, organic materials and overcoming them with EGaIn to determine their dielectric properties and provide realistic values of εr

Fullerenes for organic electronics

Dit proefschrift beschrijft de synthese en toepassing van fullerenen in plastic electronika. Fullerenen bestaan geheel uit koolstof en vormen een kooistructuur. Ze hebben de bijzondere eigenschap dat ze zeer goed elektronen kunnen accepteren en geleiden. De mate waarin elektronen geaccepteerd worden is van groot belang voor verschillende toepassingen. In dit proefschrift zijn de volgende toepassingsgebieden onderzocht: plastic zonnecellen, plastic transistoren en holografische materialen. Geprobeerd is, door chemische modificatie, het elektronen accepterende vermogen van fullerenen te veranderen. We laten zien dat wanneer fullerenen gebruikt worden in zonnecellen het van belang is dit elektronen accepterende vermogen te verminderen. Hierdoor kunnen hogere voltages bereikt worden. Voor het gebruik van fullerenen in transistoren is het belangrijk dat deze fullerenen stabiel zijn aan de lucht. Door het elektronen accepterend vermogen te verhogen is, voor het eerst, gebleken dat er luchtstabiele transistoren gemaakt kunnen worden. Holografische materialen, worden gebruikt als medisch diagnotische techniek. Met deze techniek kunnen opnames van weefsel onder de huid gemaakt worden. Eén component in het materiaal is fullerenen. We laten zien in dit proefschrift dat, hoe beter het fullereen elektronen accepteert, hoe beter de resolutie van het beeld wordt. De snelheid waarmee een dergelijk hologram gemaakt, gelezen en gewist kan worden is zo snel dat er videobeelden van gemaakt kunnen worden. De laatste hoofdstukken zijn van meer theoretische aard. We laten hier een nieuwe manier zien om de elektronische eigenschappen van fullerenen, door middel van chemische modificatie, te veranderen. Als laatste wordt de synthese van gigantische parelketting structuren beschreven.

Two new types of π-conjugation between a fullerene sphere and an addend

Diazirine addition reactions to C60, followed by an HCl elimination step, yielded [6,6] and [5,6] sp2 carbon bridged fullerenes. The [5,6] adducts (alkylidenehomofullerenes) are the first examples of fullerene structures where the addend is attached to the fullerene cage in a true, albeit highly bent, alternating single–double bond fashion.

1064-nm Sensitive Organic Photorefractive Composites

Organic photorefractive composites with sub-second response time and complete internal diffraction efficiency at low-intensity 1064 nm illumination are presented. Direct sensitization of the composites is provided by the C84 fullerene derivative [84]PCBM or the organic/inorganic hybrid Ni-dithiolene complex TT-2324. Holographic measurements on blends with varying contents of sensitizer are demonstrated.

Charge Transfer Dynamics in Polymer-Fullerene Blends for Efficient Solar Cells

Blends of poly(3-hexylthiophene) (P3HT) and the bis-adduct of [6,6]-phenyl-C61-butyric acid methyl ester (bisPCBM) show enhanced performances in bulk-heterojunction solar cells compared to P3HT:PCBM thin films due to their higher open-circuit voltage. However, it is not clear whether the decrease of the short-circuit current observed in P3HT-bisPCBM blends originates from the 100 mV reduction of the offset between the lowest unoccupied molecular orbitals of the donor and the acceptor or from a change in the morphology. The analysis of the photoluminescence dynamics of the various bulk heterojunctions provides information on the dependence of the electron transfer process on their microstructure. We find that in solution, where the donor-acceptor distribution is homogeneous, the photoluminescence dynamics is the same for the bis- and PCBM-based blends, while in thin films the first shows a slower dynamics than the second. This result indicates that the reduction of the LUMO offset of ~100 meV does not influence the electron transfer efficiency but that the diversity between the photoluminescence dynamics in thin films should be ascribed to the different microstructure of the bulk heterojunctions fabricated with the two acceptors.

Air-Stable n-Channel Organic Transistors Based on a Soluble C84 Fullerene Derivative

Air-stable n-channel organic transistors are fabricated using a newly synthesized soluble fullerene derivative. The airstable nature of this molecule allows the realization of complementary circuits under ambient conditions without encapsulation. As shown in the figure, the I-V characteristics of the devices are retained even after exposure to air for a week. To the best of our knowledge, this is the first demonstration of an air-stable electron-transporting fullerene-based molecule

Fullerene Bisadducts for Enhanced Open-Circuit Voltages and Efficiencies in Polymer Solar Cells

A fullerene bisadduct can enhance the efficiency of polymer:fullerene bulk heterojunction solar cells. The bisadduct has a LUMO that is 100 meV higher compared to that of [6,6]-phenyl C-61 butyric acid methyl ester (PCBM). This increases the open-circuit voltage of polymer: fullerene bulk heterojunction solar cells based on poly(3-hexylthiophene) and bisadduct PCBM to 0.73 V, while maintaining high fill factors and currents