High-Efficiency Organic Solar Cells Based On Liquid Crystal Molecular Materials

Organic Solar Cells(OSCs)are considered a highly promising photovoltaic technology due to their light mass,low cost,flexible translucency,solution treatability and the ability to manufacture devices on a large scale.In recent years,the performance of OSCs has been continuously improved due to the emergence of strategies such as innovation in photovoltaic materials,optimisation of device processes and regulation of interfacial layers;however,compared to the well-developed silicon-based solar cell technology,the efficiency and stability of OSCs still need to be improved,hindering the pace of commercialisation of OSCs.Liquid crystal molecular materials are materials with both crystalline and liquid properties,featuring well-defined and highly repeatable structures,ordered and oriented properties,high electrical conductivity and crystallinity.The performance of OSCs can be enhanced by utilising the characteristics of liquid crystal molecular materials to broaden the light absorption range,improve charge transport and optimise the film morphology;therefore this thesis systematically investigates the application of liquid crystal molecular materials in OSCs.The main research of this thesis is as follows:(1)Direct involvement of liquid crystal molecules--third element application: the liquid crystal molecular material BTR-Cl was introduced as a third element into the D18-Cl:N3 system to achieve efficient and stable ternary OSCs.based on the principle of similar compatibility and crystallographic differences,the liquid crystal small molecule BTR-Cl was selected for efficient ternary OSCs;when 20% of BTR-Cl was introduced,the structural similarity between D18-Cl and The structural similarity between BTR-Cl allows for good film compatibility,which not only contributes to efficient energy transfer,but also leads to an improved morphology of the active layer,when the device performs best,with a maximum efficiency of 17.92%,significantly higher than that of the binary D18-Cl:N3 device.In-depth results show that the liquid crystal small molecule donor plays multiple roles in the host system as a third element,acting as an energy level mediator,an energy transfer and charge transport intermediary and a morphology modifier with multiple roles coordinated together to optimise the morphology and improve the electrical properties,not only in terms of efficiency,but also to substantially improve the stability and detectability of the device.(2)Indirect Influence of Liquid Crystal Molecules--Additive Applications: The addition of the liquid crystal small molecule material BTR-Cl as a solid additive to the highly efficient binary system PM6:BTP-eC9 to build highly efficient and stable binary OSCs.3% of the BTR-Cl liquid crystal molecule material was added to the PM6:BTPeC9 based device and the device efficiency increased from 16.53% to 17.86%..It was found that there was good compatibility between BTR-Cl as a solid additive and PM6 and BTP-eC9,which could act well with the host system.The optical,electrical and morphological properties of the OSCs were analysed,and due to the strong self-assembly and crystallinity of the liquid crystal molecule BTR-Cl,the active layer morphology can be modulated;the liquid crystal molecule directly optimises the roughness,molecular stacking and crystallinity in the active layer morphology,thus promoting the OSCs electrical processes of exciton dissociation,charge transport and collection and improving the device Stability improvement.