Investigation Of Nanoscale Interfacial Thermal Transport Characteristics Of Organic Semiconductor Heterostructures

Organic semiconductors,the important new electronic materials with rapid development,have attracted wide attention of researchers in the past 20 years.Since the energy transfer and transport characteristics of organic semiconductor materials can directly affect the properties and applications of organic semiconductor materials,exploring the energy transfer and transport in organic semiconductor materials is an important research content of organic electronics.Compared with inorganic semiconductors,the energy transmission mechanism of organic semiconductor materials is more complicated,which puts forward higher requirements and challenges for their practical applications.Especially,the heat transport performance of organic semiconductors is far away from that of inorganic semiconductor materials.The heat dissipation capacity of organic semiconductor materials can directly affect their structural stability,which in turn has a huge impact on the performance and lifetime of the organic devices.In this thesis,molecular dynamics(MD)simulation methods were used to simulate and calculate the interfacial thermal transport performance of heterostructures based on organic semiconductor materials.This investigation explored the influence factors of thermal transport at the interface of organic semiconductor heterojunctions,studied the interfacial heat transport mechanism of organic semiconductor heterojunction,and developed an effective method to improve the interfacial heat transport performance of organic semiconductor heterojunction.The specific research content and main results are as follows:(1)Using the MD simulation method,an organic semiconductor-two-dimensional material heterostructure model was constructed.The transient thermal pulse method was utilized to calculate the numerical value of the interfacial thermal boundary resistance of the organic semiconductor-two-dimensional material heterostructure.The effects of the interface size and thickness of the organic semiconductor layer in the simulation on the value of interfacial thermal boundary resistance were verified.It was found that the interfacial thermal resistance is different under different organic semiconductor molecular orientations.This research showed that as the increase of system temperature,the defect content of the two-dimensional material and the interface coupling strength,the interface thermal resistance of the organic semiconductor-two-dimensional material heterojunction will decrease.Meanwhile,the phonon state density of the material at the interface was calculated to reveal the reason of interfacial thermal boundary resistance variation,Moreover,12 artificial neural network models were built to predict the interfacial thermal boundary resistance.The influence of the number of layers of the neural network and the number of neurons on the prediction performance was also explored.and then an artificial neural network model with the smallest mean square error and the best prediction effect was obtained.(2)The interfacial thermal transfer models of metal-organic semiconductor heterostructures were established,and the nonequilibrium molecular dynamics simulation method was used to calculate the interfacial thermal conductance of metal-organic semiconductor heterostructures.The self-assembled monolayers(SAMs)were used to modify the metal interface,and the heat transport performance of the metal-SAM-organic semiconductor structure was calculated.It was found that the SAM molecule can act as a"phonon bridge" to enhance the heat transfer at the interface.The investigation found that different SAM molecules will result in different interfacial thermal conductance and the polarity of the SAM functional group is an important factor which may affect the enhancement performance.The difference in the polarity of SAM functional groups will lead to differences in interfacial properties such as interface adhesion energy,atomic density,pair interaction distance and hydrogen bond numbers,which in turn affects the value of the interfacial thermal conductance.Therefore,the SAM molecule with the functional group of carboxyl group(-COOH)has the best improvement capacity of the interfacial thermal conductance.(3)Based on the research of thermal transport performance of the metal-SAM-organic semiconductor composite structure,a variety of SAMs molecules with different carbon chain lengths were constructed to modify the metal interface.The carbon chain length effect of SAMs with different functional groups on interfacial thermal conductance were compared,and it was found that the SAMs with functional group of methyl had more obvious carbon chain length effect.Mixing SAMs with different carbon chain length,it was found that the interfacial thermal conductance shows a trend of first decreasing and then increasing.Mixing SAMs with different functional groups,it was found that both the interfacial thermal conductance and the interface adhesion energy show a linear variation trend.This investigation explored the effects of carbon chain length effect and SAM binary mixing effect on the interfacial thermal transport characteristics,calculated the contribution rate of vibrational frequency in interfacial thermal conductance,and provided a complete understanding for the SAM molecules to improve the interfacial thermal transport characteristics.