Wide Bandgap Donor Materials With Deep HOMO Energy Level For Non-fullerene Polymer Solar Cells

Organic solar cells(OSCs)have attracted widespread attention as a simple,efficient,and environmentally friendly photoelectric device.OSCs become more convenient for people's daily life because of the great advantanges of light weight,solution processability,flexibility and wearability.During the past decades,the non-fullerene based OSCs with single junction achieved the PCE over 18%because of the wider absorption wavelength and easy to adjust energy levels of non-fullerene acceptors.The development rapidly benefits from the design concept of D-A polymer donor,but it still shows many disadvantages,such as low currents and mismatch with the energy level etc.Moreover,the efficiency materials of medium-and wide-bandgap are limited(such as PM6,PTB7-Th,and J71).Therefore,we should not only continuing to optimize the D-A polymer donor materials,but also increase the exploration of new polymer donor structures.This article was divided into three works,the wide bandgap polymer donors were designed and synthesized based on A1-?-A2 type and A1-A2 type structure and through the side chain engineering to adjust the absorption and energy level.The main research contents of this thesis are as follows:1)In this work,we designed and synthesized two novel electron-deficient units 4TC and C4T.After alternately copolymerized with another electron-deficient unit BTZ,two wide-bandgap polymer donors PBTZ-4TC and PBTZ-C4T of A1-?-A2 type were synthesized.In addition,the long alkyl side chains can improves the solubility of the polymer donor and optimizes the molecular morphology.After introducing electron-dificient(A)units,which can effectively reduce the highest occupied molecular orbital(HOMO)energy level of the polymers and well matched with the non-fullerene acceptor ITIC-Th1.The thiophene as a ? bridge can effectively reduce the steric hindrance between adjacent groups,improving the planarity of the polymer backbone and achieving a balance of electron and hole.Therefore,the polymer PBTZ-4TC was obtained a high power conversion efficiency(PCE)of 8.7%,the PBTZ-C4T shows better PCE of 9.34%.The result demonstrate that ester substituted thiophene of polymer PBTZ-C4T is more conducive to obtain high device performance in OSCs.These results reveal that concept of A1-?-A2 type copolymers not only can afford more flexibility in tuning the energy levels to achieve the deep HOMO levels,but also can provide a facial strategy to greatly enrich the types of polymer donors for high performance OSCs.2)In this work,we designed and synthesized three novel copolymers based on A1-A2 architecture with different side chain and ?-bridge,namely PBDD-BTZ-1,PBDD-BTZ-2 and PBDD-BTZ-3.it is found that the side chain engineering and optimization of the polymer backbone not only increase the absorption coefficient of the polymers,but also further regulate the energy levels of the polymers and surface morphology of the active layer,which ultimately improve the short circuit current(Jsc)and open circuit voltage(Foc).The polymer PBDD-BTZ-3 achieved a high open circuit voltage of 1.1 V and the PCE is 7.3%.Although the device performance of these new polymers in this work still lags behind those of the state-of-art devices,these results still reveal that the A1-A2 type polymers can enrich the donor materials and will open a new possibility in developing efficient polymers to boost the Voc in OSCs.3)Three new polymer donor materials PBDT-C4T,PBDT-F-C4T and PBDT-SF were designed and synthesized.The benzodithiophene(BDT)substituted by S and F atoms as rich-electron units and C4T as electron-deficient units.It is found that the Foc of the PBDT-SF-C4T device can reached 0.99 V,which is currently the highest voltage value based on the IT-4F acceptor.In addition,the intramolecular non-covalent interactions of S…F and S…O in the C4T block facilitate molecular packing.The PBDT-F-C4T:IT-4F shows a stronger face-on orientation.Therefore,after processing with non-halogen solvents 1,2,4-trimethylbenzene(TMB),the PBDT-F-C4T:IT-4F blend obtain a high conversion efficiency of 12.5%.These results indicate that the synergetic effect of energy band structure and molecular geometry can provide effective molecular design strategies for high-performance organic solar cells.