Optimize Of Mechanical And Electrical Properties Of Active Layer Of All Conjugated Polymer Solar Cells By Acetonitrile Additive

All-polymer solar cells(all-PSCs)have unique advantages in the field of flexible electronics due to their light weight,solution processability and intrinsic stretchability.To realize the application of all-PSCs in wearable devices,the electrical and mechanical properties of active layer need to be further improved.The photoelectric conversion process of organic solar cells mainly occurs in the active layer formed by the blending of donor and acceptor,the phase separation structure of the active layer has great influence on the photoelectric conversion efficiency.However,due to the poor thermodynamic compatibility of the components in all-polymer blends,the acceptor tends to form large phase separation structures after blending.Moreover,the electrical and mechanical properties of all-polymer active layers have a trade-off.High crystallinity is beneficial to carrier migration,but it also leads to brittleness.The complex morphology of all-polymer blends is easy to change when mechanical deformation occurs,this makes the active layers difficult to maintain electrical properties while stretching.In view of the above problems,we introduced solution additive acetonitrile to optimize the aggregation of molecules in the film,reduce the degree of phase separation,and form a fiber-liked network structure that is beneficial to the synergistic improvement of electrical/mechanical properties.On this basis,we studied the electrical properties of all polymer active layers after stretching under different conditions.The main conclusions are as follows:1.By introducing acetonitrile additives,we constructed fiber-liked network morphology in J52-2F:N2200 system,which improved the mechanical properties of the film.N2200 with high molecular weight has a strong tendency to aggregate,thus N2200 forms larger size phase separation structure within the film.The acetonitrile additive can shield part of the electrostatic potential on the surface of N2200 molecule by non-covalent interaction with N2200,reduce the non-covalent interaction between N2200 segments,improve the coplanarity of main chain and reduce the matrix network size of N2200.At the same time,the interference of J52-2F crystallization and aggregation is reduced,which enhances the ordered aggregation and face-on π-πstacking of J52-2F.Therefore,the phase separation degree of the blend film is reduced,the interface of donor and acceptor is increased,and the favorable morphology of the fiber-like network is formed.In the presence of acetonitrile volume fraction of 1.5%,the fracture strain is increased from 19.8%to 31.0%.2.The optimization of morphology by adding acetonitrile additives is beneficial to the improvement of the electrical properties of the active layer and the electrical stability after stretching.The PCE of additive-free J52-2F:N2200 device prepared by transfer printing method is 6.94%.The PCE of which changes can be divided into three stages with the increase of tensile strain:(1)PCE drops slowly within the strain of 030%;(2)when the strain is 30-40%,the change of morphology leads to the rapid decrease of PCE;(3)when the strain is more than 40%,the film is destroyed and there is no electrical property.After the addition of acetonitrile,the electrical stability of the film is improved.When the acetonitrile content is 1.5%,active layer was stretched to 50%,the PCE decreased from the initial 7.78%to 6.47%,which maintained 83%of the initial PCE.