Morphology Manipulation Of The Photoactive Layer In Roll-to-roll Gravure Printed Organic Solar Cells

With the advantages of light weight,low cost,flexible and shape-able,solution processing and roll-to-roll printing compatibility,organic solar cells are of great potential in diversified energy supply application scenarios,attracting much attention from researchers.In recent years,thanks to the design and synthesis of new materials,the optimization of the phase separation morphology of the active layer and the continuous progress of the preparation process,the efficiency of small area single junction organic solar cells has exceeded 19%,laying the cornerstone of efficiency for the commercial practical application of organic solar cells.However,the most of high-efficiency organic solar cells are based on small-area devices prepared by laboratory spin-coating methods.To advance the development process of their practical applications,it is necessary to expand the area to achieve high speed roll-to-roll mass production with guaranteed device performance.Gravure printing has been used in the preparation of flexible organic solar cells due to its advantages of high throughput,high resolution and pattern-ability.Nevertheless,its research progress in organic solar cells has lagged behind,mainly because the thermodynamic instability of the fluid makes the film uniformity cannot be maintained.For photovoltaic devices,film uniformity is the basis for achieving good performance.To address the problem of uniformity of gravure printed active layer films,this work focuses on the interfacial interaction between Zn O substrate and organic photoactive layer ink in inverted structured organic solar cells.From the perspective of suppressing liquid film instability,large-area homogeneous active layer films were obtained in that way.We finally prepared highly efficient flexible devices with an area of1 cm² with gravure-printed AgNWs/Zn O/Active layer films.The specific study is divided into two main sections,as follows:1.To overcome the problem of unstable wet films of organic photoactive layers in gravure printing,this work proposes a strategy for modulating the interfacial adhesion to the substrate.It has been shown that active layer films gravure printed on substrates with the introduction of silver nanowires can effectively suppress or even eliminate their unstable flow.The mechanism of action of silver nanowires in the wetting and levelling process has been investigated in depth by the construction of cross-linked network structures with different degrees of sparseness and density for the adjustment of the substrate surface roughness.The influence of the substrate surface morphology on the quality of the photoactive layer film in gravure printing has been revealed.Based on the above findings,a mechanical model between substrate roughness and interfacial adhesion is developed in this thesis to explain the mode of action of interfacial adhesion between substrate and ink from the perspective of experimental and interfacial adhesion theory for different wetting states.By increasing the roughness of the substrate,the contact area of the solid/liquid interface can be effectively expanded and the interfacial adhesion improved,resulting in a homogeneous large-area organic photoactive layer with an efficiency of 9.87%for a 1 cm² flexible device prepared with gravure-printed AgNWs/Zn O/PM6:BTP-BO-4Cl film.2.In order to solve the problem of uniformity of the organic photoactive layer for gravure printing,this thesis also develops an ink for gravure printed organic photoactive layer.This ink is not affected by the substrate during gravure-printing process resulting better printing stability.The introduction of a surfactant enhances the intermolecular adsorption between the ink and Zn O,preventing the unstable slippage of the wet film of the active layer and achieving uniform film formation in gravure printing.The results show that surfactants can both improve the macroscopic homogeneity of the film and influence the phase separation morphology of the active layer film.The introduction of surfactants increases the orderliness of the molecular structure.The CCL value is reduced,which somewhat inhibits excessive aggregation of molecules.The efficiencies of gravure printed inverted structure flexible organic solar cells with an area of 1 cm² based on the non-fullerene PM6:BTP-BO-4Cl system reached 11.87%and over 13%for the ternary PM6:BTP-BO-4Cl:PC₆₁BM system.