Sunday, November 16, 2014

How to measure the difference between electron and hole mobilities

Measuring the mobility of electrons and holes

Picture of transported electrons or holesSimilarly as in TOF, the mobility of both electrons and holes can be measured using photo-CELIV. The key idea is to photogenerate the surface charge in thick films with thicknesses much larger than the light absorption depth (or photogeneration profile due to Beer-Lambert law (d >> αd)). As can be seen from the Figure shown here, the extraction of either electrons or holes through the film can be chosen by applying forward or reverse bias, or, if forward bias injects shows too heavy injection, then illumination from different electrodes can be done keeping the same applied bias.
The disadvantage of this type of experiment is that typically thick films, on the order of micrometers or more, are required. Typical thickness of organic electronic devices is much less, meaning that typically the faster carrier mobility can only be measured from CELIV in operational devices.

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