The Exploration Of "Limited Diffusion Alloy" Strategy To Improve Efficiency And Stability

Recently,organic solar cells have attracted widespread attention due to their numerous advantages,including light-weight,thin-thickness and flexibility,solution-processability,and easily regulated absorption energy level.These features make this technology highly suitable for indoor photovoltaic,semitransparent devices,flexibility and wearable devices.The efficiency of organic solar cells has been rapidly improved,greatly promoting the commercialization process of organic solar cells.The rapid advance is benefitted from the design of narrow band gap small molecule acceptors and wide band gap conjugated polymer donors,particularly the A-DA’D-A-type small molecular acceptors.The most extensively used approach is the modification of aromatic-core and the terminals via chemical synthesis,which is also the crucial method for enhancing the performance of organic solar cells.Therefore,this study aimed to design and synthesize a series of new acceptors based on the aromatic-core engineering and terminal A-units engineering on those of A-DA’D-A-type small molecular acceptors.This study systematically investigated the structure-properties relationship between molecular structure and device performance.The key points of this paper are summarized as followings:1.We designed and synthesized a new acceptor material,ZCCF3,and added it to PM6:Y6 system as the third component.This approach forms a“diffusion-limited acceptor alloy”,which involves adding a third component to the OSCs for enhancing both the efficiency and stability of the device.This led to significant improvements in the device performance:the open-circuit voltage of the device was increased from 0.84 V to 0.86 V,the short-circuit current was increased from 25.83 m A cm^-2 to 26.95 m A cm^-2,and the fill factor was increased from 77.40%to 80.01%.As a results,the maximum efficiency reached 18.54%,which is also the highest efficiency of PM6:Y6-based devices.Importantly,device stability has been largely improved(T₈₀ from 40 hours to360 hours).Our result suggested that the addition of ZCCF3 promotes the dissociation of excitons and its high glass transition temperature（T_g）of ZCCF3allow it form acceptor alloy with Y6 that suppresses the diffusion of the acceptors and enhances the stability.2.On the basis of success of the"diffusion-limited acceptor alloy"in Chapter 2,we designed and synthesized two ZCCF3-derivatives,namely ZCCF3-BO and ZCCF3-FBr.When added to the PM6:BTP-eC9-based devices,two acceptors increase the open-circuit voltage of the device（from 0.846 V to0.869 V and 0.863 V,respectively）.Additionally,the addition of ZCCF3-BO also increased the short-circuit current and fill factor of the device,resulting a final efficiency reached 18.18%.Our final results demonstrated that the"limited diffusion alloy"strategy can be successfully implemented in the BTP-eC9 based system with appropriate modifications to ZCCF3.