Investigation Of Growth And Thermal Transport Characteristics Regulation Of Organic Semiconductor Nanocomposite Structures

Organic semiconductors as an important component of organic electronics,have received a great deal of attention from researchers in recent years for their rapid development.The growing practical applications demand increasingly stringent requirements on the performance and reliability of organic electronic devices,including smaller device sizes to meet a wide range of applications,higher power density to ensure device performance,and superior heat dissipation capability to ensure stable device operation.The core of organic electronic devices lies in the growth of high-quality organic semiconductor thin films,and the key is to achieve an ordered stacking structure of organic semiconductor molecules for optimal charge carrier transport.Meanwhile,organic semiconductors are highly temperature-sensitive and have poor thermal conductivity.The electrical characteristics of organic devices are easily affected by temperature,which can cause significant changes in the electronic structure of organic semiconductors and thus affect device performance.Charge carrier transport and phonon thermal transport in organic semiconductor materials are important research topics in organic electronics,and effectively improving the thermal transport of organic semiconductors is crucial for device performance.Previous studies have shown that embedding metal nanoparticles into organic semiconductor materials can significantly enhance the electrical properties of nanocomposites.Therefore,exploring the thermal transport characteristics of metal-organic semiconductor nanocomposites by incorporating nanoparticles into organic semiconductors and altering the various characteristics of nanoparticles is essential to ensure the structural thermal stability of organic electronic devices and promote their efficient operation and performance.In this thesis,molecular dynamics(MD)simulations are applied to simulate the tunable growth of organic semiconductor films,and the effect of metal particles on the thermal transport of organic semiconductor materials is investigated,the interfacial thermal transport mechanisms of the metal-organic semiconductor nanocomposite are revealed,and effective methods to strengthen the thermal transport performance of metal-organic semiconductor nanocomposites are proposed.The specific research contents and main results are as follows:(1)Using MD simulations,we investigate the deposition and growth process of organic semiconductors on metal surfaces modified with different self-assembled monolayers(SAMs).The effects of substrate surface roughness,SAM and deposition temperature on the growth of organic semiconductor films are investigated.The pentacene molecules forms upright films on the rough SAM-modified Au substrate surface,and grow better on the SAM(-COOH)-modified Au substrate.The interaction energies between the organic semiconductor molecules and the substrate are evaluated,and it is found that the energy exchange between the pentacene molecules and the substrate provides the driving force for reorientation.The calculations of the free energy on the pentacene film surface and substrate reveal that the effect of surface roughness on the location of nucleation and the Ehrlich-Schwobel barrier on the growth of upright crystal islands.It is demonstrated that surface roughness changes the distribution of free energy and thus affects nuclei formation and orientation.The Ehrlich-Schwobel barrier at the edge of the film prevents interlayer spanning of the pentacene molecules.The study investigates the dynamic growth of organic semiconductor pentacene films on metal surfaces functionalized with SAM,providing the necessary guidance for the efficient preparation of organic electronic devices.(2)The thermal transport models for metal-organic semiconductor nanocomposites are constructed and non-equilibrium molecular dynamics(NEMD)simulations are applied to investigate the thermal conductivity of metal-organic semiconductor nanocomposites modified with different SAMs.N,N’-diphenyl-N,N’-di(3-methylphenyl)-(1,1’-biphenyl)-4,4’diamine(TPD)is selected as organic semiconductor molecules to evaluate the effects of Au core diameter,SAM type and SAM chain length on thermal conductivity.The study shows that the thermal conductivity of the nanocomposites can be significantly enhanced by SAM molecules,and the increase in SAM chain length and Au core diameter can significantly enhance the thermal conductivity of the nanocomposites.The variations of thermal conductivity of the nanocomposites are elucidated by the the vibrational density of state and thermal conductivity contribution decomposition.The comparison of the vibrational density of states shows that SAM can significantly enhance the vibrational coupling with Au in low frequency vibrational modes and introduce overlapping contributions with TPD in medium frequency vibrational modes.The decomposition of the thermal conductivity of metal-organic semiconductor nanocomposites suggest that non-bonding interactions dominate the thermal transport.The normalized radial density of TPD and the atomic number density at different interfaces are counted to demonstrate the interfacial characteristics between nanoparticles and organic semiconductors.It is shown that the thickness of the van der Waals region formed by the nonbonding interaction increases with chain length,tighter bonding between TPD and SAM molecules reduces the obstruction to the thermal transport in the nanocomposite.Quantum chemical calculations are used to compare the weak interactions between TPD and different SAMs.The π-π stacking interaction between TPD and SAM(-C6Hs)molecules is better than the van der Waals interaction between TPD and SAM(-COOH)molecules.The study provides valuable information for the thermal management of organic electronic devices by improving the thermal conductivity of metal-organic semiconductor nanocomposites.(3)Based on the barriers of thermal transport in metal-organic semiconductor nanocomposite,a metal-organic semiconductor interfacial thermal transport model is constructed to evaluate the effects of SAM type and SAM chain length on the interfacial thermal transport of nanocomposite structures.It is shown that the modification of metal nanoparticles by SAM can significantly improve the interfacial thermal transport of metal-organic semiconductor nanocomposite structures.The increase in SAM chain length can significantly reduce the temperature difference between Au nanoparticles and TPD molecules and enhance the interfacial thermal transport of nanocomposites.The effect of different weak interactions and chain lengths on the interfacial thermal transport of the nanocomposite structures is demonstrated by calculating the atomic number density.The dynamic behavior of TPD molecules on NP surfaces modified with different chain lengths of SAM is observed and the insertion depths of TPD molecules on different NP-SAM surfaces are counted.The atomic number density at the nanocomposite interface increases after the addition of SAM,the adhesion energy between the nanoparticles and the organic semiconductor increases,the phonon scattering at the interface decrease,and the sufficient mixing of nanoparticles and TPD molecules at the interface greatly reduce the interfacial thermal resistance.The Free energy analysis at the nanoparticle surface is performed to elucidate the dynamic behavior of the organic semiconductor.The free energy analysis shows that the presence of SAM gaps leads to significant free energy fluctuations and that TPD molecules readily enter the lower energy regions of the nanoparticle surface,thus forming strong interactions with the nanoparticles.The study aims to analyze the interfacial thermal transport of metal-organic semiconductor nanocomposites to provide guidance for the regulation of the thermal performance of organic electronic devices.