The Preparation And Photovoltaic Properties Study Of High Efficiency Benzodifuran-based Polymer

With the development of technology,the global demand for energy is increasing rapidly year by year.At present,the issues of energy pose severe challenges to various countries on the earth about the further development of the economies.According to statistics,Chinese energy consumption structure is still dominated by fossil energy,coal and oil and gas still account for 90% of Chinese energy consumption.However,the reserves of traditional fossil energy are limited,and it will cause environmental pollution as well,which is not conducive to sustainable development.As a type of clean energy,solar energy has many advantages like large reserves,no pollution,and wide distribution.It is considered to be one of the most promising new type of clean energy sources in the 21 st century.Therefore,seeking the way to convert the solar energy has become a hotspot of research.Organic solar cells?OSCs?have the advantages of a wide range of sources,low cost,non-toxic,light weight,large area device can be prepared by spin coating,printing,and roll-to-roll.Has become the focus of research by scientists around the world.In the past thirty years,scientists have optimized the performance of organic photovoltaic devices by optimizing material synthesis,device structure,manufacturing process,etc.Especially in the last ten years,the power conversion efficiency?PCE?of single-junction organic solar cells has increased from less than 10% to nearly 17% now,showing a bright future of development and application.The rapid development of organic polymer cells in recent years is very gratifying.However,the polymer donor materials which are widely used are mainly based on benzodithiophene?BDT?,However,thiophene as a kind of petrochemical product its widespread use runs counter to the concept of clean energy's development,so the polymer based on benzo[1,2-b:4,5-b']difuran?BDF?is considered as the substitute for BDT,mainly because of its wide variety of sources and environmental protection.At present,the study of furan-based polymer donor materials has attracted the attention of many scientific researchers.BDF-based materials also exhibit similar photovoltaic performance as BDT-based materials.However,the solar cell constructed by BDF is still lags behind the BDT-based OSCs in terms of types and power conversion efficiency.In order to a further study on BDF-based polymers,this article designed two unreported D-A type polymer donor materials based on benzodifuran,and blend with non-fullerene acceptor as the active layer to fabricate the OSCs.And study their photovoltaic properties,the work is divided into the following two aspects:In order to reduce the electron donating ability of the side chain and enhance the degree of conjugation to improve the planarity of the molecule,we chose benzene to replace the thiophene unit on the side chain to optimize the morphology of the thin film.Use alkylbenzene side chain and benzo[1,2-b:4,5-b']difuran as the donor unit,with the bisfluorobenzotriazole?Bz?is used as the acceptor unit synthetic the polymer PPBDFTBz?F12?,After a series of optimizations,it was shown that PPBDF-TBz:Y6 based OSCs can achieve a PCE of 9.50% in the inverted devices,which shows an excellent shortcircuit current density(J_sc)22.4 m A/cm2 and a fill factor?FF?68.86%.Due to the matching energy level and absorption spectrum of PPBDF-TBz and Y6,which PCE is similar to the polymer PTBDF-TBz reported in our previous work,the J_sc and FF of the device show a significant improvement compared with the thiophene-based polymer donor material J52,due to the good compatibility of the alkylbenzene with BDF and stronger degree conjugation between the molecule,which proves the feasibility of using benzene replace thiophene units on the side chains of BDF-based polymers.In order to study the influence of acceptor units of the polymer,we selected dithiophene-4,8-dione?BDD?as the acceptor unit with alkylfluorobenzene as the side chain and synthesized a polymer based on BDF,named 4FP-BDD.Its absorption spectrum concentrated at 500 nm to 650 nm,which is very complementary to the nonfullerene acceptors that can absorb in the near infrared region?NIR?.When blended with ITIC-4F,the device got a PCE of 9.19%,and its HOMO energy level was-5.63 e V,which provided an open-circuit voltage(V_oc)of 0.9 V.In this paper,a variety of acceptors were selected and matched with our polymer donor to study the effect of difference of HOMO energy level between donor and acceptor on device performance.In addition,we found that optimization the manufacturing processes of device such as high temperature thermal annealing,solvent vapor annealing?SVA?,and using of some additive like 1,8-diiodooctane?DIO?to increase the crystallization of the acceptor molecule,the V_oc of the device will be reduced,and this article investigates the phenomenon.