Design And Synthesis Of Novel Wide Band-gap Donor Materials And BN Materials For Organic Solar Cells

In recent years,organic solar cells?OSCs?have the advantages of light weight,flexibility,translucency,and roll-to-roll large-area processing.They have great potential in new energy sources and have received extensive attention and research.The rapid improvement of photoelectric conversion efficiency is inseparable from the researchers'efforts in the design and synthesis of novel materials,the optimization of device processing technology and the exploration of device physics.This dissertation focuses on the novel wide band-gap donor materials and BN materials,and explores the influence of polymer molecular weight,alkyl side chains,aggregation types,novel polymerization units and terminal groups on the performance of organic solar cell devices.Based on the characterization,the morphology,photophysics and other properties of the corresponding system were explored.The molecular weight of the polymer has an important influence on the device performance of organic solar cells.In Chapter 2,based on the polymer donor PNQx-2F2T,we investigated the effect of polymer molecular weight on device performance of fullerene PC₇₁BM and non-fullerene IT-M systems.It is found that fullerene-based devices prefer higher polymer molecular weight,while non-fullerene devices are not susceptible to the molecular weight of PNQx-2F2T.The device results are extensively explained by electrical and morphological characterizations.This work not only evidences the potential of NQx for constructing high performance photovoltaic polymers but also demonstrates a useful structure-performance relationship for efficiency enhancement of non-fullerene OSCs via the development of new conjugated polymers.Based on the Chapter 2,we explore the influence of donor alkyl side chains on the performance and morphology of devices in different systems.In Chapter 3,we explored the effect of the donor alkyl side chain on the performance and morphology of devices in different systems.In Chapter 3,we investigate the influence of side chain length of polymer donors based on a set of random terpolymers PTAZ-TPD10-Cn on the device performance of polymer solar cells with three different acceptor materials,i.e.fullerene acceptor PC₇₁BM,fused-ring molecular acceptor ITIC,and polymer acceptor N2200.Shortening the side chains of polymer donors improves the device performance of PC₇₁BM-based devices but deteriorates the ITIC-and N2200-based devices.Morphology studies unveil that the miscibility between donor and acceptor in blend films depends on the side chain length of polymer donors.Upon shortening the side chains of the polymer donors,the miscibility between the donor and acceptor increases for the PC₇₁BM-based blends,but decreases for the ITIC-and N2200-based blends.In this chapter we explore the interaction of polymer structure,blend films morphology and device performance.In addition to the significant influence of polymer molecular weight and alkyl length on device performance,the packing mode of small molecular semiconductors in thin films is an important factor that controls the performance of their optoelectronic devices.In Chapter 4,three structurally-related diketopyrrolopyrrole?DPP?based molecules are synthesized to study the effect of replacing C-C bonds by isoelectronic dipolar B?N bonds.By replacing one of the bridging C-C bonds on the peripheral fluorene units of the DPP molecules by a coordinative B?N bond and changing the B?N bond orientation,the optical absorption,fluorescence,and excited state lifetime of the molecules can be tuned.The substitution alters the preferential aggregation of the molecules in solid state from H-type?for C-C?to J-type?for B?N?.The photovoltaic properties of the DPP molecules are evaluated in bulk-heterojunctions with fullerene acceptor and reveal moderate performance as a consequence of suboptimal morphologies,bimolecular recombination,and triplet state formation.Introducing B?N bonds therefore provides a subtle way of controlling the packing mode.Based on the previous chapters,in Chapter 5 we designed and developed a novel BN wide band-gap donor polymer materials PBNBDD-46/68 with a tricoordinate BN unit.Through device optimization,based on PBNBDD-46:PC₇₁BM organic solar cells,a photoelectric conversion efficiency of 5.4%was obtained.hrough the investigation of photoelectric properties and morphology,it is found that the weak crystallinity of polymer and the poor blend film morphology limit the device efficiency.In addition,we have explored the triplet energy level of the material through various characterization methods such as low-temperature phosphorescence PL,magnetic field photocurrent MPC,electroluminescence EL,etc.,and proved its high E?T₁?,small?E_ST energy level.It shows that the tricoordinate BN unit may bring high E?T₁?properties,which will be beneficial to suppress triplet recombination.Although the work has not obtained high efficiency device,it has accumulated experience for the design and synthesis of nonmetallic triplet materials for organic solar cells.Designing and synthesizing non-fullerene small molecules have become research hotspots in organic solar cells.Based on the Chapter 5,it is known that the BN-Ph unit is a weak donor unit with good planarity and easily adjustable side chain.In Chapter 6,we designed and synthesized novel BN small molecule acceptor materials with different end groups to regulate the energy level,absorption and other properties of the molecule.Fullerene organic solar cells.After device optimization,the device based on BN-Ph-F achieved a photoelectric conversion efficiency of 4.6%.These results indicate that the BN unit also has certain potential in the preparation of highly efficient non-fullerene acceptor materials.