Carrier localization on surfaces of organic semiconductors gated with electrolytes

Organic semiconductor single crystals gated with electrolytes exhibit a pronounced maximum in channel conductance at hole densities >1013cm ^-2. The cause is a strong decrease in the hole mobility with increasing charge density, which is explained in terms of a percolation model that incorporates trapping of holes by ions at the semiconductor-electrolyte interface. In the case of rubrene crystals, the peak channel conductance occurs at hole densities near 3×1013cm^-2. The magnitude of the effect will be large for semiconductors with low dielectric constants and narrow bandwidths, and thus is likely to be a general phenomenon in organic semiconductors gated with electrolytes.