Synthesis And Application Of Naphthalimide And Dithienothiophene[3.2-B]-Pyrrolobenzothiadiazole Based Polymer Acceptor For All-Polymer Solar Cells

All-polymer solar cells(all-PSCs)have great potential in the preparation of large-area flexible devices due to their excellent morphological stability and mechanical robustness.Currently,there are fewer high-performance polymer acceptors,resulting in the efficiency of all-PSCs still differing significantly from that of based on small-molecule acceptor organic solar cells.On the other hand,from small-area devices to large-area devices,the poor adoption of the materials to printing methods and the large efficiency loss are still great challenges.In this thesis,mainly based on the understanding of the relationship between the structure of photovoltaic materials and device performance,a series of polymer acceptors based on naphthalimide and dithieno[3.2-b]-pyrrolobenzothiadiazole were designed and synthesized around improving the spectral absorption of polymer acceptors and optimizing the active layer morphology,while investigating the relationship between molecular structure and performance.The specific research work and results are as follows:1.The dye groups were introducedrhodanine-based dye molecule by random copolymerization in the highly crystalline NDI-based polymer N2200,and the polymer acceptors PNDI-2T-TR(5)and PNDI-2T-TR(10)were obtained.It was found that the introduction of dye groups could effectively enhance the light absorption coefficient of the polymer acceptors and facilitate the short-circuit current(J_SC);meanwhile,the random copolymerization could reduce the crystallinity of the polymers and optimize the active layer morphology.The devices based on PBDB-T:PNDI-2T-TR(5)demonstrated a high power conversion efficiency(PCE)of 8.13%under the conditions of no additives and annealing.2.To further investigate the relationship between molecular structure and active layer morphology,we designed two types of polymer acceptors around the modulation of the spectral absorption of NDI-based polymers and the miscibility with the donor.First,we synthesized NDI-based terpolymer acceptors PNDI-2FT-0.1,PNDI-2FT-0.2and PNDI-2FT-0.3 with different 3,3'-difluoro-2,2'-bithiophene(2FT)molar ratios by random copolymerization,and it was observed that the absorption coefficients of all these terpolymers were improved.Also the terpolymers formed by random copolymerization have better miscibility with the PBDB-T.The devices based on PBDB-T:PNDI-2FT-0.1 showed a high PCE of 9.46%,and exhibited excellent thickness stability.Subsequently,a series of novel naphthalimide based terpolymer acceptors PNDI-2FT-TRx(x=10,20)were synthesized by introducing TR and 2FT units through random copolymerization.Due to the synergistic effect of TR units with fluorine atoms,the absorption coefficients of the terpolymer acceptors were not only improved,but also the active layer morphology was optimized.The PCE of PM6:PNDI-2FT-TR10-based devices reached 10.71%,which is one of the highest values among all-PSCs based on NDI system.More importantly,the PM6:PNDI-2FT-TR10-based devices exhibit excellent thermal stability and film thickness stability.3.In order to bridge the performance gap from small-area devices to large-area devices,we propose to use a non-conjugated polymer molecular design strategy to modulate the crystallinity as well as the mechanical properties of polymer receptors,and we synthesized a series of non-conjugated polymer acceptors(PTH-Y,PTCl_m-Y,and PTCl_o-Y).It was found that that non-conjugated polymer acceptor can effectively minimize the technique and efficiency gaps between small-area spin-coating method and large-area blade-printing,and facilitate the preparation of large-area flexible device.By directly inheriting the spin-coating condition,the blade-coating processed device based on PTCl_o-Y achieves an impressive PCE of 12.42%,comparable to spin-coating processed one(12.74%).Such non-conjugated polymer system even can well tolerate large-scale preparation and flexible substrate.Notable PCEs of 11.94%for large-area hard device and 11.56%for large-area flexible device are achieved,which is the highest value for large-area flexible all-PSCs by blade-coating.In addition,non-conjugated PTCl_o-Y-based devices show excellent thermal stability and mechanical robustness.These results demonstrate that the non-conjugated polymer acceptors are potential candidates for fabrication of highly-efficient,large-area and robust flexible all-PSCs by printing methods.4.To improve the absorption coefficient of the polymer receptor,we introduced selenophene into the acceptor to synthesize the polymer PYSe,and to regulate the miscibility between acceptors and donor,a series of random copolymerization receptors PYSe-TClx(x=10,20 and 30)were synthesized by introducing 3-chlorothiophene through random copolymerization.When PBDB-T was chosen as the donor,the PCE of all-PSC based on PBDB-T:PYSe-TCl20 was up to 14.21%and the J_SC of 23.08 m A cm^-2,which was superior to PBDB-T:PYSe(12.45%).To further optimize the active layer morphology,we chose PTCl_o-Y as the third component added to prepare the three components.When the addition amount was PBDB-T:PYSe-TCl20:PTCl_o-Y(1:1.1:0.1),the device efficiency improved to 15.26%,and mainly the FF improved to 72.1%.More importantly,PBDB-T:PYSe-TCl20:PTCl_o-Y is well used in large-area(1.21 cm²)all-PSCs with an PCE of 13.81%,which the highest value based on blade-coated large-area all-PSCs.In addition,the PBDB-T:PYSe-TCl20:PTCl_o-Y based all-PSCs showed good stability,which is favorable for future large-scale preparation.