(Color online) Chemical structures of (a) PCBM, (b) Ketolactam-1, and (c) bis-PCBM (one possible isomer). (d) HOMO and (e) LUMO spin densities for a ketolactam quasifullerene (equivalent to Ketolactam-1 with a truncated alkyl side chain) as calculated by DFT.
Ultraviolet photoelectron spectra (UPS) and inverse photoemission spectra (IPES) taken from thin-films of (a) bis-PCBM and (b) Ketolactam-1 for experimental determination of the electronic structure of fullerenes.
AFM images of thin films of (a) PCBM, (b) Ketolactam-1, and (c) bis-PCBM.
DSC thermograms during the first heating and cooling cycles obtained from drop-cast material of each of the three fullerenes studied here. The enthalpy of fusion for PCBM is deduced from the area under the melting endotherm.
Transistor characteristics obtained from bottom gate top contact (Al) transistors. W = 1500 μm and L = 200 μm. (a) Saturation regime transfer characteristics at VD = 50 V for all three fullerenes (inset: device structure used in the present study). Output characteristics of the same devices using (b) PCBM, (c) Ketolactam-1, and (d) bis-PCBM.
(a) Example plot of transmission line method extraction of contact resistance using transistors based on PCBM with Au top contacts (L = 200 μm, W = 1500 μm). (b) RContact /RChannel ratio for each semiconductor/electrode system investigated in this report (L = 200 μm, W = 1500 μm).
Air stability of fullerenes. (a) Saturation mobility (VD = 50 V) as a function of atmospheric exposure time (μt > 0) normalized to the saturation mobility measured under inert conditions (μt = 0). (b) Threshold voltage as a function of atmospheric exposure time.
(a) Arrhenius plots of the linear regime drain current (VD = 1 V, VG = 50 V) for all three fullerenes. Lines are best fits for the extraction of the activation energy in the moderate temperature region. (b) Gate voltage dependence of the activation energy (moderate temperature) of the drain current in the linear regime.
Summary of material and device parameters. μsat and VT were extracted from devices with L = 20 μm, W = 1500 μm and Al top contact electrodes at VD = 50 V. Mobility as a function of exposure time (μt > 0) was extracted from devices with L = 50 μm, W = 1500 μm and Au top contact electrodes at VD = 50 V
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