After more than three decades of molecular and carbon-based electronics, the creation of airand thermally stable n-type materials remains a challenge in the development of future p/n junction devices such as solar cells and thermoelectric modules. Here we report a series of ordinary salts such as sodium chloride (NaCl), sodium hydroxide (NaOH) and potassium hydroxide (KOH) with crown ethers as new doping reagents for converting single-walled carbon nanotubes to stable n-type materials. Thermoelectric analyses revealed that these new n-type single-walled carbon nanotubes displayed remarkable air stability even at 100 o C for more than one month. Their thermoelectric properties with a dimensionless figure-of-merit (ZT) of 0.1 make these new n-type single-walled carbon nanotubes a most promising candidate for future n-type carbon-based thermoelectric materials.

We measure the gap density of states and the Fermi level position in thin-film transistors based on pentacene and dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) films grown on various surfaces using Kelvin probe force microscopy. It is found that the density of states in the gap of pentacene is extremely sensitive to the underlying interface and governs the Fermi level energy in the gap. The density of gap states in pentacene films grown on bare silicon dioxide (SiO(2)) was found to be larger by 1 order of magnitude compared to that in pentacene grown on SiO(2) treated with hexamethyldisilazane and larger by 2 orders of magnitude compared to that of pentacene grown on aluminum oxide (AlO(x)) treated with a self-assembled monolayer (SAM) of n-tetradecylphosphonic acid (HC(14)-PA). When DNTT was grown on HC(14)-PA-SAM-treated AlO(x), the gap density of states was even smaller, so that the Fermi level pinning was significantly reduced. The correlation between the measured gap density of states and the transistor performance is demonstrated and discussed.

Crystalline domain size and temperature dependences of the carrier mobility of commonly used pentacene polycrystalline films on SiO2 have been studied by four-point-probe field-effect transistor measurements. The mobility is found to be proportional to the crystalline domain size and thermally activated. This behavior is well explained by a polycrystalline model with the diffusion theory, and thereby the barrier height at boundary and the mobility in domain are calculated to be 150meV and 1.0cm2∕Vs, respectively. The in-domain mobility is lower than those expected in single crystals, which suggests that there exist some other limiting factors of carrier transport than the domain boundaries.

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