Charge Transfer At Organic-Organic Interface And Its Impact On Transistor Performance

Electronic devices based on organic semiconductors as the main active layer such as organic light emitting diodes(OLEDs),organic photovoltaic(OPV)cells and organic field-effect transistor(OFET)are one of the hot research topics in recent decades.The performance of these devices depends on the charge carrier transport at the metal-organic and organic-organic heterogeneous interfaces,and the free carrier transport occurs in the Highest Occupied Molecular Orbital(HOMO)and Lowest Unoccupied Molecular Orbital(LUMO)energy levels of organic molecules.Therefore,understanding the physical properties of organic-organic heterojunctions is essential to optimize the performance of organic electronic devices.However,due to the complex effects of charge transfer,dipole interaction,and doping,the organic-organic interface properties are not only related to the chemical structure and interfacial microstructure,but also heavily dependent on the ambient atmosphere.Therefore,in order to clearly understand the charge transport effects at the organic-organic interface,in situ growth in a vacuum environment without air exposure and real-time photoelectric property monitoring are highly needed to fully understand and elucidate the interfacial mechanism.In this thesis,we construct organic-organic heterogeneous interfaces and use in situ deposition for realtime electrical characterization to trace the effects on device performance as the top semiconductor is deposited;and we construct heterogeneous structural systems with different electronic structures to comparatively study the organic-organic interface charge transfer effect and its impact on transistor performance.The research mainly includes following two aspects:1.The interfacial charge-transfer effect of pentacene/VOPc was investigated using a laboratory-built in situ real-time electrical characterization equipment,and the intrinsic charge-transfer effect at the organic-organic interface and its enhancement characteristics for electron transport were observed.By comparing the conventional ex situ sample preparation and electrical characterization results,it is found that this intrinsic interfacial charge transfer effect is severely suppressed during the ex situ experiments.In addition,experimental and theoretical analyses show that the enhancement of electron transport capacity lies in the pentacene/VOPc interface effect,where electrons are transferred from the pentacene side to VOPc side and accumulated on the VOPc side due to the difference in energy level structure at the interface,thus increasing the electron carrier concentration in the conducting channel and enhancing the electron transport capacity.In contrast,the electron transport in devices after pentacene deposition of the top semiconductor in ex situ experiments is almost unchanged,but the hole transport capacity is slightly decreased,which is attributed to the fact that O2/H2O doping in air in pentacene/VOPc interfacial effect,trapping the interfacial carriers and inhibiting the electron transfer process.This work is a guide to understand the organic-organic interface effect,optimize the device performance,and explore the optimal process.2.Based on the previous work,in order to investigate the influence of different organic heterogeneous interfacial electronic structures on the charge transport behavior,we further constructed NPN and NPP type heterogeneous structures to further investigate the modulation of hole-electron carrier transport behavior by energy band structure and semiconductor layer properties.Combined with the evolution of transistor device performance and low-temperature transport studies,the different "accumulation" and"depletion" behaviors of interfacial charge transport are explored to provide a theoretical and experimental basis for a comprehensive understanding of the carrier transport behavior at organic-organic interfaces;and the preliminary exploration of the role of multilayer It also explores the application of multilayer organic heterostructures in photo responsive transistors,which provides a basis for expanding the application of organic heterostructures in light detection.