In Situ Studies Of The Film-forming Mechanism Of Organic Nanofilms Based On Grazing Incidence X-ray Scattering Technology

Organic nanofilms have special physicochemical properties and can exhibit unique microstructure as well as photovoltaic properties,and therefore have broad application prospects in the field of photovoltaics.The key to improving the photoelectric conversion efficiency of organic thin film solar cells is to obtain organic nanofilms with excellent photovoltaic properties and use them as active layer structures.Therefore,how to efficiently prepare organic nanofilms for solar cells has become the focus of current research.It is of great significance to improve the performance and stability of organic thin film solar cells by exploring the evolution of the internal microstructure of the film preparation process.In this paper,the film-forming process of two organic nanofilms in the field of photovoltaic was studied in situ.One is the thermally induced self-assembly process of block copolymer films,and the other is the scraping film-forming process after blending the acceptor materials.The synchronous radiation grazing incidence X-ray scattering（Grazing incidence X-ray scattering,GIXS）technology was used to observe the internal microstructure of the organic nanofilm during the preparation process in real time,so as to reveal the law and mechanism of the formation of the internal microstructure of the film.The research contents and conclusions are as follows:（1）The ordered structure formed by self-assembly of PS-b-PMMA block copolymers can be used as a structure-directing layer to adjust the structure distribution inside the active layer.In this paper,the thermal induced self-assembly process of PS-b-PMMA block copolymer films was studied in situ by grazing incidence small angle X-ray scattering（GISAXS）.By analyzing the evolution of the internal lamellar structure of the film,it was found that when the temperature was higher than the glass transition temperature,the internal lamellar structure of the film first reorientation.It was found that when the temperature was higher than the glass transition temperature,the lamellar grains in the film first reoriented.After 150°C,the lamellar repeat period L₀ increased rapidly from 32.6 nm to 41.9 nm.In the heat preservation stage,the grain sizeξrapidly increases by more than 1000 nm,while the lamellar repeat period L₀ of lamellae is almost unchanged.This result shows that the formation of ordered structure in PS-b-PMMA film mainly includes phase separation process and grain growth process.At the same time,the effect of heating rate on the internal structure of the film was explored.The results show that the thermal induced self-assembly process can obtain better ordered nanostructures at higher heating rate.（2）Blending film of donor and acceptor materials is the key process of fabricating active layer materials for solar cells.The forming mechanism of PM6:Y6 blend film by blade-coating was investigated by in situ GIXS and UV-vis absorption spectrum.Combined with in situ UV-vis and GISAXS,the light absorption ability and internal phase separation process of the film were explored.Grazing incidence wide angle X-ray scattering（GIWAXS）was used to observe the internal crystallization and orientation arrangement of the film.The results showed that the film-forming method of PM6:Y6mix film was divided into three stages:at first,the dissolution stage was created,at this point,the receptor material was absolutely dissolved within the solvent,and no specific structure was formed;secondly,the nucleation and growth phase,as the solvent gradually volatilizes,the molecules begin to nucleation and gradually grow up,forming an anisotropic internal arrangement structure;finally,after solvent evaporation,the internal structure of the film tends to be stable,and finally forms a stable morphology.In addition,the correlation between the blade speed and the formation of the internal structure of the film was explored,and it was found that the film showed a structural morphology that was more conducive to exciton transmission under the appropriate scraping rate,thus showing a better photoelectric conversion efficiency（PCE）of solar cells.