Study the effect of distribution of density of states on the subthreshold characteristics of an organic field-effect transistor (OFET)

Abstract

In the existing theory for organic field-effect transistors (OFETs) the effect of molecular order on the subthreshold characteristics is ignored. This effect is studied analytically through the potential profile and subthreshold swing at a weak accumulation mode. The developed theory predicts a wide accumulation region and a low subthreshold swing for a poorly ordered semiconductor. Simulation of transistors with various distributions of density of states is performed to mimic OFETs made of regioregular-Poly 3 hexylthiophene (rr-P3HT). The simulation results support the analytical equation for the potential profile. Furthermore, the effect of molecular order on the subthreshold swing matches with the theory. However, the analytical value for the subthreshold swing is greatly underestimated mainly due to an oversimplified model used for mobility.

Effect of Polymer Binders on UV-Responsive Organic Thin-Film Phototransistors with Benzothienobenzothiophene Semiconductor

“…In the dark, all the devices showed good characteristics for solution-processed OTFTs, that is, negligible hysteresis, low gate (leakage) current (Figure S5), high On/Off ratio, and mobility comparable with those reported for small molecule/ dielectric polymer blends used as active channel materials. 38 The threshold voltage strongly depends on the fabrication conditions, dielectric/polymer interface, and chemical nature of the active channel components. Since all the studied OTF-PTs were fabricated under the same conditions, we can consider only the influence of the polymer composition on V Th.…”

“…The quality of the interface in the used blends is investigated upon charge trap density ( N trap,dark ), the inverse subthreshold slope (SS) and the density of deeper traps at the interface ( D it ). N trap,dark was estimated using the equation N trap = ( |V Th | C ox )/ q , where q is elementary charge, while SS (the slope of the linear part of log I D – V G curves at V G < V Th ) was calculated using the equation SS = ( d log I D / dV G ) −1 , D it values were calculated based on the inverse subthreshold slope and D it = [( q SS log­( e )/ k B T ) – 1] C ox / q 2 , assuming that the density of deeper traps in a semiconductor and at polymer/semiconductor interface are independent of the energy under the same fabrication conditions and with the same semiconductor. , k B and T are the Boltzmann constant and absolute temperature, respectively. All the above-mentioned parameters, which were estimated as the mean values from five devices of each type of OFT-PTs, are summarized in Table .…”