Abstract
The stability of doped organic semiconductors is one of the essential features to achieve stable and high-performance organic optoelectronic devices with low power consumption. In this study, the thermal degradation of an organic homojunction, consisting of an intrinsic organic layer and a molybdenum oxide (MoO3)-doped organic layer, is investigated by impedance spectroscopy (IS) under thermal heating. The IS analysis indicates that the thermal deformation of the intrinsic organic layer is more significant than that of the underlying doped organic layer. A charge-transfer complex absorption peak analysis by ultraviolet-visible spectroscopy confirms that the thermal degradation is related to the deformation of organic host molecules rather than to diffusion of dopants. These results show that the organic homojunction is degraded owing to the crystallization of intrinsic organic molecules at high temperatures, above the glass transition temperature (Tg), rather than because of disruption of the interface at the homojunction by dopant diffusion. This study shows that hole-transport molecules having high Tg should be selected to provide stable electronic devices with organic homojunctions, thus paving the way for the development of novel devices with higher performance.
Highlights
Organic semiconductors (OSs) have attracted significant interest in the development of flexible, wearable, and mobile optoelectronic devices owing to their flexibility, light weight, design freedom on different types of substrates, and simple fabrication by various methods such as thermal evaporation under high vacuum and solution processes under atmospheric pressure
Device I is heated at temperatures in the range of room temperature (RT) to 110 ○C, while device II is heated at temperatures in the range of RT to 160 ○C owing to the different glass transition temperatures (Tg) of the hosts
For the intrinsic NPB (i-NPB) layer, a constant phase element (CPE) component was selected instead of simple capacitance as the CPE component is more suitable for evaluating a parameter when the intrinsic organic molecules gradually lose their electrical properties due to a deformation of the layer or modification of their electrical characteristics by impurities in the layer
Summary
Organic semiconductors (OSs) have attracted significant interest in the development of flexible, wearable, and mobile optoelectronic devices owing to their flexibility, light weight, design freedom on different types of substrates, and simple fabrication by various methods such as thermal evaporation under high vacuum and solution processes under atmospheric pressure. The fundamental background of the doping technique for OSs is not very similar to that for inorganic semiconductors, electrical doping increases the free-carrier densities of doped OSs, as in inorganic semiconductors This enables reduction in the driving voltage and power consumption of organic optoelectronic devices. The electrical doping in OSs aims to match the Fermi energy levels between OSs and metal electrodes This reduces the charge injection barrier between them, which helps us achieve Ohmic-like contact.. IS enables us to directly analyze the device under electrical operation without damage or destruction of the device and thin films Utilizing these advantages, in this study, we investigated the stability of doped OSs by IS. We carried out a temperature- and time-dependent IS analysis of an organic homojunction composed of an intrinsic organic layer on a doped OS layer
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