Research On Ternary Organic Solar Cells And Its Film Thickness Tolerance

Organic solar cells（OSCs）have broad application prospects in both the military and civilian fields due to their unique advantages,such as light weight,easy preparation,and flexibility.In recent years,OSCs have achieved rapid development,but its power conversion efficiency（PCE）is still low compared with the silicon-based solar cells and the emerging perovskite solar cells.Further improvement of PCE is still the focus of OSCs research.As we all know,the PCE of OSCs is very sensitive to active layers thickness.Increasing the thickness of active layers lead to a significant reduction of PCE,which is also a key problem to be solved in large-scale production of OSCs.Ternary strategy has been widely demonstrated to be an efficient way to improve the performance of OSCs and inherit the simple manufacturing process used for binary OSCs.It is expected to become the first choice for the commercialization of OSCs in the future.Due to different physicochemical properties of used materials,the introduction of the third component will make the internal working mechanism of ternary OSCs more complicated.In this paper,in order to improve the PCE of OSCs and reduce the sensitivity of device performance to active layers thickness,a systematic study was carried out on the relationship between the material physicochemical properties,preparation process,working mechanism and device performance.The performance of OSCs can be improved by selecting appropriate material and optimizing film-forming kinetics process of active layers,and the internal reasons for performance improvement of ternary OSCs are explained in ternary OSCs of various systems.The main research contents and innovations of this paper can be summarized as follows:（1）The OSCs of J71:T6Me:IT-4F and PM6:BTP-4F-12:IT-M were prepared by the material selection method based on complementary photovoltaic parameters of binary OSCs.In the ternary system of J71:T6Me:IT-4F,J71,T6Me and IT-4F have obvious complementary absorption spectra.Incorporating appropriate IT-4F can effectively supplement the obvious absorption spectra dip of J71:T6Me blend films,leading to enhanced photon harvesting of ternary active layers.In PM6:BTP-4F-12:IT-M ternary system,PM6,BTP-4F-12 and IT-M have cascade energy levels,incorporation of IT-M can effectively adjust energy levels of ternary active layer.In addition,the incorporation of appropriate IT-M can also optimize the morphology of ternary active layers.（2）The exciton dynamics between two acceptors was studied by characterizing current density versus voltage curves of cells without donor and the photoluminescence spectra of acceptors blend films,which can effectively identify charge transfer or energy transfer process between two acceptors.The formation of alloy states between two acceptors was verified by studying compatibility of materials and varied energy levels of two acceptors dependence on their relative content.The process of charge separation in ternary OSCs was studied by using magneto-photocurrent,which provides a more solid basis for analyzing internal reasons of performance improvement of ternary OSCs.（3）Ternary OSCs based on PM7:Y6:PC₇₁BM were prepared by combining the advantages of fullerene and non-fullerene acceptors.The incorporation of PC₇₁BM can effectively improve the electron mobility of ternary active layers,which makes the optimized ternary active layers have higher charge mobility and more balanced electron and hole transport.In addition,the incorporation of PC₇₁BM can be used as a morphology regulator to effectively regulate the molecular arrangement,phase separation degree and domain size in ternary active layer,revealing the relationship between the morphology evolution of active layers and performance of OSCs.（4）The reflection spectra of OSCs and the special device with PMMA as active layers were measured.The absorption spectra of active layers in OSCs can be obtained by the difference between reflection spectra of OSCs and special device,which can really reflect the contribution of third component on photon harvesting.Raman mapping measurements were carried out on the blend films to characterize the distribution of each component in ternary active layers,which provides a strong reference for better understanding of the internal reasons for the performance improvement of ternary OSCs,the working mechanism and the charge transfer process in active layers.（5）A new material selection method for thick-film OSCs was proposed based on the complementary photovoltaic parameters of binary OSCs,besides the high carrier mobility of third component.The PM7:BP-4F:MF1 and PM6:BP4T-4F:BP3T-4F based ternary thick-film OSCs were successfully fabricated according to this strategy.Compared with corresponding binary OSCs,the optimized ternary OSCs exhibit improved PCE and good active layer thickness tolerance.This paper has a total of 63 pictures,16 tables,and 191 references.