Performance Studies Of PM6:Y6 Based Ternary Organic Solar Cells

As a promising renewable energy technology,organic solar cells have advantages of light weight,translucency,flexibility,and environmental protection.Generally,the active layer of an organic solar cell is mainly composed of one donor material and one acceptor material.While ternary organic solar cells with a third component can enhance the absorption,optimized morphology of active layers,improve the efficiency of exciton dissociation and charge transport,and ultimately improve the power conversion efficiency（PCE）.Ternary organic solar cells not only maintain the simple preparation process of binary organic solar cells,but also can enhance the capture of photons of devices through introducing the third component.The active layers in ternary organic solar cells have become more complicated in the morphology and carrier dynamics process,and it is necessary to be further explored the internal working mechanisms to explain the improvement of device performance.The studies take high-efficiency binary organic solar cells as the starting point.By selecting a suitable material as the third component,the capability of photon capture,the efficiency of exciton dissociation and charge transport and the performance of the devices are supposed to be improved.Through material and device characterization,the role of the third component and the internal working mechanism of the improvement of the performance of the ternary organic solar cells are studied.The main researches are as follows:（1）The non-fullerene acceptor ITIC with a medium band gap was used as the third component and introduced into PM6:Y6 binary system to successfully fabricate PM6:Y6:ITIC ternary organic solar cells.Compared with PM6:Y6 binary devices,the short-circuit current density(J_SC),open circuit voltage(V_OC)and fill factor（FF）of PM6:Y6:ITIC ternary devices have been improved simultaneously,and the PCE of ternary devices increased to 16.6%from 15.5%of PM6:Y6 binary devices.The absorption spectrum of ITIC is complementary to that of PM6:Y6 binary system,which enhances the photon capture capability of devices.At the same time,an alloy model with energy transfer is supposed to exists in PM6:Y6:ITIC ternary organic solar cells,which significantly improves exciton dissociation and carrier transport efficiency in the active layers.The balanced electron-hole mobility reduces molecular recombination and energy loss in the ternary devices.This work shows that using acceptor with energy transfer process as the third component in an alloy model can effectively improve the performance of ternary organic solar cells.（2）An organic small molecule material BTB is used as the third component in PM6:Y6 binary organic solar cells for the first time.The interaction between BTB molecules and Y6 molecule changes the steric hindrance of the acceptor molecules,and improves the absorption,optimizes the morphology and interpenetrating network structure of the active layers,therefore improves exciton dissociation,charge transfer and collection efficiency.When the proportion of BTB molecules in the acceptor is 1 wt%,the J_SC and FF of the devices are significantly improved,and the PCE of the optimal ternary devices exceeds 16.7%.In addition,the introduction of BTB is conducive to improving the stability of the devices.After 18 hours of storage at 70℃,the PCE remain>60%of the initial PCE,while the PCE of the devices without BTB is reduced to 45%of the initial PCE.When the BTB molecules are applied to the PM6:BTP-BO-4F system,the optimal PCE of the ternary devices exceeds 17.3%.The results of PM6:Y6:BTB ternary system and PM6:BTP-BO-4F ternary system proved that BTB molecules are suitable for ternary organic solar cells in general.