Empirical Modeling of Photoenhanced Current–Voltage Hysteresis in PEDOT:PSS/ZnO Thin-Film Devices

Abstract

“Hybrid” organic–inorganic semiconducting devices consisting of zinc oxide (ZnO) thin films coated with poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) with Au and Al surface electrodes have been fabricated and electrically characterized. In dark condition, devices with Au electrodes exhibited ohmic behavior, while Al electrodes resulted in diodic behavior. These devices demonstrated photostimulated current–voltage (I–V) hysteresis, in which dissimilar electrical current is observed based on the voltage sweep direction, notably as a function of the illuminated wavelength exposed on the device surface during electrical characterization. Ultraviolet-induced oxygen desorption on the ZnO surface, leading to electrons transitioning into the conduction band, gives rise to an increase of accumulated charges within the ZnO/PEDOT:PSS dipole interface. This effect was found to produce a hysteresis effect that increased under ultraviolet illumination. Characteristic I–V hysteresis was empirically modeled using a series of first-order multiple linear regression expressions that decouple device processing and characterization conditions. The numerical markers of hysteresis in I–V traces, including first-order estimates of scaled and shifted transformations, were modeled. The results of this analysis indicated that illumination is statistically a stronger explanatory variable for hysteresis than all other parameters, which further suggests that space charges stored on the dipole interface more significantly influence hysteresis than do trapped charges alone.