Synthesis And Photovoltaic Properties Of Ternary Polymer Donors Based On Oligothiophene-Benzothiadiazole Units

With the development of society and fossil resources has been continuously depleting,the renewable resource is needed.Solar energy is regarded as the ideal alternative energy,due to its merit of clean,pollution-free and inexhaustible.Especially,polymer solar cells（PSCs）have the advantages of low cost,light weight and good flexibility.Developing PSCs with excellent performance and improving photoelectric conversion efficiency are the key points of research.Recently,the power conversion efficiency of PSCs has been exceeded 14%by designing and selecting different materials,ratio for the acceptor,and optimizing the device.Among them,ternary polymer donor materials can combine the advantages of different electron donor units and electron-deficient units to adjust the absorption and energy levels of materials,improving the performance of polymers.In this thesis,we synthesized a series of D-A alternating terpolymers utilizing alkoxy-substituted benzothiadiazole（ROBT）with different oligothiophene units.We expect to obtain high performance PSCs by optimizing material structure and properties.（1）In the 3 chapter,Two kinds of D1-A-D2-A polymer donor materials,namely P1 with regular structure and PR1 with random structure,were designed by ROBT unit,thiophene（TT）and trithiophene（3T）units through different synthetic routes.For the terpolymers PR1 and P1,the S···O intermolecular interaction can effectively increase the polymerization length and improve the coplanarity,exhibiting a broad absorption of 300 to 750 nm.The P1:PC71BM based device achieved an optimum PCE of 3.40%with a V_OC is 0.62 V,J_SC is8.53 mA cm^-2,indicating the random polymer PR1 has more potential in PSCs.By comparing these materials,we found that different molecular configurations have a great influence on the energy level,hole mobility and morphology of the polymer material.（2）In the 4 chapter,Based on ROBT,TT and monothiophene T units,four D1-A-D2-A ternary random polymers were synthesized,namely PROBT-25,PROBT-50 and PROBT-75 PROBT-100.These random terpolymers have broad absorption（300-800 nm）and suitable HOMO/LUMO level.After a series of device optimizations,it is found that the PROBT-50 polymer donor material exhibits a higher PCE of 4.05%at a ratio of 1:1.This may be because the molecular weight of PROBT-50 is higher than PROBT-25 and PROBT-75.Although the molecular weight of PROBT-100 is also high,its lower solubility is not conducive to form of a better film morphology,resulting in reduced efficiency.PROBT-50 has good solubility and can be dissolved in solvents such as chlorobenzene,which is beneficial to form a better film morphology and thus facilitate the balance of holes and electrons.By adjusting the ratio of polymer monomers,random polymerization can improve the performance of PSCs.（3）In the 5 chapter,2D/A type of terpolymers（P0,PR0）with similar polymer backbones based on ROBT,TT and bithiophene 2T were synthesized.Comparing the experimental results in Chapter 3,we changed the 3T unit to the bithiophene（2T）unit in attempted to increase the PCE of polymer.After the electrochemical performance and device optimization of P0 and PR0,it was found that although the PCE of random polymer PR0 is higher than the regular P0,both devices are less PCE than PR1.The lower solubility of P0 and PR0 is the main cause of lower PCE,and the other reason is that it is sensitive to temperature and cannot be dissolved by heating,and it is impossible to construct favorable charge transport.Although these polymers are similar in structure,small differences in structure can lead to very different performance.