Influence of film structure and light on charge trapping and dissipation dynamics in spun-cast organic thin-film transistors measured by scanning Kelvin probe microscopy

Abstract

Herein, time-dependent scanning Kelvin probe microscopy of solution processed organic thin film transistors (OTFTs) reveals a correlation between film microstructure and OTFT device performance with the location of trapped charge within the device channel. The accumulation of the observed trapped charge is concurrent with the decrease in ISD during operation (VG = −40 V, VSD = −10 V). We discuss the charge trapping and dissipation dynamics as they relate to the film structure and show that application of light quickly dissipates the observed trapped charge.

Identification of grain boundaries as degradation site in n-channel organic field-effect transistors determined via conductive atomic force microscopy

“…We believe that our results further complete the picture that grain boundaries not only lead to local charge trapping upon device operation in p‐channel transistors , but also in the still emerging field of n‐channel materials grain boundaries can act as traps for charge carriers.…”

“…Here, we study the influence of the grain boundaries on bias stress using conductive atomic force microscopy (c‐AFM) in the n‐type semiconductor EH‐PDI‐CN. Our study complements recent Kelvin probe studies on p‐type materials such as TESADT , pentacene and C 8 ‐BTBT in which the trapping of charges at grain boundaries or step‐edges upon charging of the semiconductors was observed.…”

Visualization of trapped charges being ejected from organic thin-film transistor channels by Kelvin-probe force microscopy during gate voltage sweeps

“…[9][10][11] In previous KFM experiments on the charge trapping in OTFTs, the distribution of the carriers trapped in deep states whose lifetime is comparable or longer than the measurement time was studied. [12][13][14][15][16] This is because the surface potential mapping by the KFM typically takes more than several tens of seconds or several minutes, and thus, it is hard to evaluate transient phenomena that take place on a faster time scale. Recently, an alternative technique similar to KFM that can visualize the trapped charges through the measurement of the local threshold voltage by applying an ac modulation voltage to the gate electrode was reported by Ando et al 17 Since the OTFT device is in the accumulation regime during the gate voltage modulation during this method, the measured trapped charge distribution represents that during the device operation.…”