Internanocrystal coupling induced excitons dissociation in lead salt nanocrystal assemblies is investigated. By combining transient photoluminescence spectroscopy, grazing incidence small-angle X-ray scattering, and time-resolved electric force microscopy, we show that excitons can dissociate, without the aid of an external bias or chemical potential gradient, via tunneling through a potential barrier when the coupling energy is comparable to the exciton binding energy. Our results have important implications for the design of nanocrystal-based optoelectronic devices.

The interplay between ionic and electronic charge carriers in mixed conductors offers rich physics and unique device potential. In light-emitting electrochemical cells (LEECs), for example, the redistribution of ions assists the injection of electronic carriers and leads to efficient light emission. The mechanism of operation of LEECs has been controversial, as there is no consensus regarding the distribution of electric field in these devices. Here, we probe the operation of LEECs using electric force microscopy on planar devices. We show that obtaining the appropriate boundary conditions is essential for capturing the underlying device physics. A patterning scheme that avoids overlap between the mixed-conductor layer and the metal electrodes enabled the accurate in situ measurement of the electric-field distribution. The results show that accumulation and depletion of mobile ions near the electrodes create high interfacial electric fields that enhance the injection of electronic carriers.

No abstract

No abstract

The comparatively high mobility of pentacene and its ability to be deposited on flexible substrates at low temperature [1,2] make it an attractive alternative to amorphous silicon in low-cost large-area electronics applications. Potential applications of pentacene thin-film transistors include display drivers, smart cards, and radio-frequency identification tags.[2±4]While pentacene thin-film transistors have exhibited usefully large mobilities (³ 1 cm 2 V ±1 s ±1 ) and on±off ratios (³ 10 6 ), [5] fabricating pentacene transistors with suitable performance for large-scale applications remains a challenge. In polycrystalline films, mobility is extremely sensitive to processing conditions, being dependent on crystallite size, [6±10]