| Organic solar cells（OSCs）have attracted the attention of scientific researchers due to their simple device structure,low manufacturing cost,easy integration,environmental friendly,can fabricate flexible,multi-colored and translucent devices and other characteristics.In recent years,the efficiency of OSCs devices has increased rapidly,and the power conversion efficiency（PCE）has reached more than 18%.Among them,the dynamic process of photo-generated excitons is one of the keys to improve the performance of OSCs.Limited by the lifetime and diffusion length of excitons in active layer,some excitons will be annihilated before they reach to the interface between the donor and the acceptor,which limits the improvement of exciton dissociation efficiency.To solve the above problems,this paper introduces delayed fluorescent（DF）materials into the OSCs,which prolongs the lifetime and diffusion length of the active layer excitons,improves its morphology,and enhances the performance of the devices.The main research contents of this paper are as follows:1.The DF material APDC-DTPA was spin-coated on the active layer of inverted OSCs based on the PBDB-T:N2200 system as an exciton supply layer to fabricate double-layer OSCs.After optimizing the speed,annealing time,and additive concentration of the exciton supply layer,the double-layer device reaches the best PCE of 8.35%,which is 33.81%higher than the conversion efficiency of the standard device（PCE=6.24%）.The experiments results show that APDC-DTPA can prolong the exciton lifetime of the active layer materials,promote the exciton dissociation process,and increase the fill factor（FF）of the devices.At the same time,the exciton supply layer can also improve the surface morphology of the active layer,optimize the contact between the active layer and the electrode,and significantly increase the open circuit voltage(VOC)of the devices.Finally,APDC-DTPA molecules were added to the active layer of PBDB-T:N2200 to fabricate ternary devices.When the content of APDC-DTPA is 20%,a high PCE of 8.84%is obtained.It shows that adding DF material into the active layer can also significantly improve the performance of OSCs devices.2.Adopting a ternary strategy,the delayed fluorescent material 7-（tert-butyl）-3,11-bis（9,9-dimethylacridin-10（9H）-yl）quinolino[3,2,1-de]acridine-5,9-dione（QAO-DAd）with better solubility is added as the tertiary material to the PTB7-Th:IEICO-4F system,which shortens the distance between the delayed fluorescent material and the active layer material,and improves the efficiency of F（?）rster energy transfer.When the content of QAO-DAd is 10%,the ternary device achieves optimal performance,and the PCE is13.01%,which is 13.53%higher than the PCE of binary OSCs（11.46%）.The addition of QAO-DAd prolongs the lifetime and diffusion length of the exciton in the active layer,improves the exciton dissociation rate of the devices,optimizes the morphology of the active layer,improves the optical and thermal stability of the devices,and improves the performance of the devices.In order to study the applicability of QAO-DAd in other systems,QAO-DAd has also been added to the PTO2:IT-4F system.The highest PCE of the optimized device is 14.07%,which is 8%more than the conversion efficiency of the binary device（13.01%）.It shows that the ternary strategy based on DF materials is one of the effective methods to improve the performance of organic solar devices.In this paper,delayed fluorescent materials are used in OSCs to construct double-layer and ternary organic solar cells,which extend the lifetime and diffusion length of excitons,and provide ideas for the preparation of high-performance organic solar cells. |
