Research On Preparation And Performance Of Highefficiency Ternary Organic Solar Cells

In recent years,the continuous development of new materials has promoted the improvement of the efficiency of binary organic solar cells(OSCs).The power conversion efficiency(PCE)has always been an important theme in the development of OSCs.In this thesis,by using ternary strategy to further broaden the absorption of active layer and regulate heterostructure morphology,can increase photon harvesting,promote the exciton dissociation and charge transport therefore improve the PCE of the OSCs.At the same time,the mechanical properties of flexible devices and the stability of rigid devices are further studied,so that can provide a strategy for the commercial application of OSCs.Firstly,we introduced the fullerene acceptor PC₇₁BM into the PM6:Y6 system and obtained the PCE of 16.67%on the rigid substrate and over 14%on the flexible substrate.Through the analysis of UV-vis absorption spectrum,it is found that PC₇₁BM has strong absorption in the short-wave region(300-500 nm),which can be complementary to the absorption spectrum of the binary system.Therefore,the light-capturing ability of the heterojunction can be improved and can reduce the loss of light energy.At the same time,we analyzed the charge collection efficiency and the recombination mechanism of the ternary systems.Due to the introduction of PC₇₁BM,the exciton dissociation and charge transfer capacity were improved,and the bimolecular recombination in binary system was reduced.The short-circuit current density(J_sc)and filling factor(FF)were effectively improved.By analyzing the evolution of voltage with PC₇₁BM content and combining with the analysis of PL spectrum,it is found that the energy transfer mechanism dominated in the first stage(when PC₇₁BM content was less than 30%),and in the second stage,the energy transfer mechanism worked together with the parallel mechanism(when PC₇₁BM content was more than 30%).After 1000 bending tests,the ITO-free device prepared on the flexible PET substrate still maintained 98%of the initial efficiency(r=7.5mm).This work provides a feasible method for the commercial application of high efficiency flexible OSCs.In the second part of the work,we tried to further regulate the morphology of PM6:Y6 system.Therefore,small molecule donor SM1 was introduced into the system,and the high PCE of 16.55%was obtained.The FF of the device was increased from73.7%to 77.5%.The structural similarity between SM1 and PM6 ensures the good compatibility between donors and forms the donor alloy phase.Due to the introduction of SM1,a small molecule donor with high crystallinity,the heterojunction molecular becomes more orderly in the ternary OSCs and show better efficiency and stability than in the binary OSCs.At the same time,the crystallization of the active layer is promoted,which creates more channels for exciton dissociation and charge transfer.Therefore,this method simultaneously improves the efficiency and stability of the OSCs to some extent,which provides an idea for the commercialization of OSCs.