Studies On High-efficiency Non-fullerene Acceptor Based Ternary Organic Solar Cells

Organic solar cells（OSCs）have attracted much attention in recent decades,improving the efficiency of the OSCs being a research hotspot in the field.The limited absorption range of traditional binary OSCs has restricted further improvement of the efficiency of single-junction cells,while the processing of the tandem device is too complicated.Based on these considerations and aiming at the core issue of how to effectively improve the power conversion efficiency（PCE）of OSCs,a series of device optimizations are performed based on the classic binary non-fullerene systems PBDB-T:IT-M and PBDB-T-2F:IT-4F.Through a large number of experiments,a suitable third component is found to optimize the active layer,which enhances the absorption of light and improves the morphology between the films.On the other hand,with the interface control as an extension,the structural design of quantum dots as the interface modification layer is systematically studied,where the contact between the active layer and the interface layer is optimized,the built-in electric field is enhanced,and the charge transfer is promoted,which paves more innovative ways to improve the efficiency of organic solar cells.The main contents are as follows:1.The small molecule acceptor DTF-IC is developed and its main mechanism for improving efficiency in PBDB-T:IT-M system is studied.It is found that when DTF-IC is used as a small molecule acceptor at 10%doping,the device efficiency can be increased to 12.14%from 10.9%.This is mainly due to the large increase in short-circuit current density(J_sc)from 16.18 m A/cm²to 17.95 m A/cm².The introduction of DTF-IC enables the donor and acceptor to form an absorption complementary state in the visible light region,and improves the photon capture of the battery in the range of 650-690 nm.In addition,there is energy transfer between the two small molecule acceptors,which helps to extract the internal DTF-IC excitons,enhances charge transfer and reduces charge recombination.In addition,the cascade energy level enables efficient charge transfer between the double acceptors,facilitating exciton dissociation and carrier transmission and collection.At the same time,DTF-IC can improve the crystallization process of the active layer while maintaining phase separation of an appropriate size.2.Using CdSe/ZnS quantum dots（QDs）as a cathode interlayer modifier,a new approach to improve the photovoltaic performance of OSCs is innovated.With this strategy,the PCE of the device is improved from 13.0%to 14.6%based on the PBDB-T-2F:IT-4F system.In order to explore the mechanisms of the significant improvement of photovoltaic performance,this paper summarizes the reasons for the improvement in photovoltaic performance from the aspects of morphology analysis,charge transfer mechanism,exciton dissociation and recombination mechanism,etc.The introduction of QDs can reduce surface layer defects of the active layer and optimize the interlayer contact.In the meantime,the synergistic effect between the QDs layer and the interface layer conduces a stronger interfacial dipole.The large interfacial dipole moment can effectively lower the work functions of electrode,thus promoting the built-in field to facilitate charge transfer and reduce the charge recombination.In addition,the extra solar energy absorbed by the QDs is decomposed into carriers at the interface between IT-4F and QDs,which contributes to the enhancement of J_sc.This paper proposes new ideas and directions for improving the efficiency of organic solar cells.