Localizing trapped charge carriers in NO2 sensors based on organic field-effect transistors

Abstract

Field-effect transistors have emerged as NO2 sensors. The detection relies on trapping of accumulated electrons, leading to a shift of the threshold voltage. To determine the location of the trapped electrons we have delaminated different semiconductors from the transistors with adhesive tape and measured the surface potential of the revealed gate dielectric with scanning Kelvin probe microscopy. We unambiguously show that the trapped electrons are not located in the semiconductor but at the gate dielectric. The microscopic origin is discussed. Pinpointing the location paves the way to optimize the sensitivity of NO2 field-effect sensors.

UV–Ozone Interfacial Modification in Organic Transistors for High‐Sensitivity NO2 Detection

“…As shown in Figure c and Figure S4 (Supporting Information), the devices without UVO treatment of the dielectric layer exhibit minimal changes in the I – V characteristics on NO 2 exposures as high as 30 ppm. This result indicates that although NO 2 is a strong oxidizing agent and can efficiently penetrate the organic semiconductor, it is apparently unable to chemically oxidize (p‐dope) the bulk of CuPc and when no NO 2 adsorption on the dielectric surface occurs, since this process alone would greatly enhance CuPc bulk conductivity and therefore I OFF of all of the present OTFTs, including those without or with brief dielectric UVO exposure. On the other hand, upon UVO treatment, large densities of oxygenated polar functionalities are produced on the dielectric surface (Figure ), which should efficiently adsorb polar molecules such as NO 2 via hydrogen bonding or van der Waals interactions .…”

Effect of Vertical Annealing on the Nitrogen Dioxide Response of Organic Thin Film Transistors

“…When the grain orientation of the OSC films is perpendicular to the conducting channel, charge carriers pass through a larger number of grain boundaries on their journey from source to drain electrodes than in a conventional device. In the band bending model, grain boundaries are represented by depletion regions, and the holes transfer via hopping from one grain to another [ 24 , 34 ]. This is in good agreement with the above phenomenon that perpendicular devices show a lower µ compared to conventional ones.…”

Achievement of High-Response Organic Field-Effect Transistor NO2 Sensor by Using the Synergistic Effect of ZnO/PMMA Hybrid Dielectric and CuPc/Pentacene Heterojunction

“…As shown in Figure 4a,b, the variations of I on and μ of device A and device B show an opposite trend along with the increasing concentration of NO 2 , the I on and μ of device B increase by 193% and 69% at 15 ppm NO 2 , while that of device A decreases by 30% and 28%. Since the I on and μ of pentacene-based OFETs will increase significantly when exposed to NO 2 atmosphere [17], CuPc might have a different impact on devices A and B. The V T of device B presents a remarkable decrease about 80%, while that of device A shows nearly no change.…”

“…Mostly, the efforts involved in developing a high performance OFET-based gas sensor are mainly focused on the OSC layers [16]. However, the interface property of dielectrics also plays a crucial role in the gas sensing characteristics, as the efficient current channel lies in the first few molecular layers of the OSC upon the dielectric layer [17]. Using scanning Kelvin probe microscopy, Andringa et al have determined that the trapped electrons of OFET-based sensors are located at the dielectric interface [18].…”