Investigation Of Interfacial Modification For Enhancing Performance And Stability Of Organic Solar Cells

Organic solar cells（OSCs）have great potential in clean energy applications.Recently,OSCs based on polymer donor and non-fullerene acceptor（NFA）has achieved a power conversion efficiency（PCE）of over 19%.However,the long-term stability of the devices severely limits the further development of OSCs.Among the factors that affect the device stability,light and thermal are the main factors.Compared to the forward devices,inverted devices have better water-oxygen stability,and have many advantages in improving the stability of OSCs.However,under ultraviolet light illumination conditions,the electron transport layer（ETL）such as Zn O used in inverted devices has many surface oxygen defects,inevitably causing interface photocatalytic degradation and degradation of the active layer material.In addition,the blend bulk heterojunction（BHJ）used in the high-efficiency OSCs system is a metastable structure.Under aging conditions such as thermal radiation,the ideal phase separation morphology of the film is destroyed,and a stable structure with obvious phase separation between the donor and acceptor is formed.Finally,the surface work function of Mo O_X hole transport layer（HTL）is unstable and has thermal diffusion problems,which seriously affects the devices performance and stability.To solve the above problems,the interface layer problems of Zn O photocatalysis and Mo O_X ion migration are solved by fine interface control.Meanwhile,a gradient distribution pseudo-planar heterojunction（PPHJ）structure is prepared to obtain a more stable donor-acceptor phase separation morphology,thus systematically improving the performance and stability of the devices.The specific research content is as follows:1.Choosing aggregation-induced emission（AIE）molecules to modify the Zn O interface not only can passivate the surface oxygen defects of Zn O film,but also can form an optical barrier layer that absorbs ultraviolet light.In the meantime,the AIE molecule can enhance both surface wettability Zn O film and vertical distribution of active layer film thus improving the device’s photovoltaic efficiency and ultraviolet light stability simultaneously.Among the three selected AIE molecules,the devices prepared by modifying Zn O with tetraphenylimidazole（TPIZ）maintained its original84%PCE after continuous irradiation with 365 nm ultraviolet light at 5 m W cm^-2intensity for 1500 hours,and its original PCE was still maintained at 80%(T₈₀)under20 m W cm^-2 intensity ultraviolet light for over 700 hours,which was the best among the three molecules.2.In order to further improve the photothermal stability of the devices,a dual-functional modification combined with a gradient morphology regulation strategy was employed to simultaneously address the Zn O,Mo O_X,and the phase separation problem of active layer.An ETB rare earth complex material was chosen for Zn O film modification.On one hand,the interaction between ETB and Zn O can passivate the surface defects and improve the conductivity,which is beneficial for promoting electron transport.On the other hand,as an optical barrier layer,it can convert absorbed ultraviolet light into visible light that can be utilized again,thereby improving the light stability and efficiency of OSCs devices.For the preparation of active layer,a sequential blade coating process was used to prepare a PPHJ active layer structure to improve the stability of the active layer phase separation morphology.To address the Mo O_X film issue,a layer of Bphen film was blade-coated as a physical barrier layer to prevent interface migration under thermal radiation conditions.Therefore,OSCs based on the ETB&Bphen-modified BTP-e C9//PM6system exhibited significantly improved photothermal stability while increasing the devices PCE.Under AM 1.5G illumination and 85℃heating,the T80 exceeded 1600hours.Moreover,this strategy was applied to the PY-IT//PM6 and IT-4F//PM6systems,both of which showed good results,demonstrating the universality of this strategy.Through this dual-interface modification strategy and sequential coating technology,we further improve the photothermal stability of OSCs,which provides a new idea for the preparation of high-efficiency and high-stability OSCs.