Synthesis Of Organic Hole-Transporting Layer Materials And Their Application In P-i-n Planar Perovskite Solar Cells

Perovskite solar cells(pero-SCs)show great potential in photoelectric field due to their advantages of high power conversion efficiency(PCE),simple processing technology,low fabrication cost,etc..Recently,the highest certificated PCE of pero-SC has reached 25.2%,which shows great promise for commercialization.Organic small molecule hole-transporting layer(HTL)materials play an important role in pero-SCs.Although p-i-n planar pero-SCs based on organic small molecule materials as HTLs have displayed a PCE of over 21%,some basic issues are still existing in organic small molecule HTL materials,such as the structure-property relationship,the design strategy of simple molecular structure and their application in large-area devices.To address aforementioned issues,this thesis systematically studied how to design and synthesize organic small molecule HTL materials to achieve high efficiency,low cost and suitability for large-area process.The corresponding results are summarized as follows:(1)Two low-cost X-shaped organic small molecule HTL materials Si-OMeTPA and SiTP-OMeTPA with silicon core and triphenylamine(TPA)derivative branches were successfully synthesized.Si-OMeTPA can be simply synthesized by two steps with low cost.The σ-π interactions between the low-lying σ orbital of silicon atom and the orbital of neighboring conjugated moiety were observed,which could enhance the molecule packing of Si-OMeTPA,thus increasing crystallinity and hole mobility.Finally,the p-i-n planar pero-SCs employing the doped Si-OMeTPA as HTL displayed a PCE of 19.06%and robust device stability.(2)X-type HTL material X1 containing pyrazine as the molecular core and TPA derivative as branches,was designed and synthesized.Compared with Si-OMeTPA,the pyrazine core not only endows X1 with good crystallinity but also improves charge transfer property and plane conjugation of molecular center,which greatly enhance the hole mobility of X1.The p-i-n planar pero-SCs based on dopant-free X1 HTL showed a PCE of 17.52%,which is nearly 15%higher than that of the device with Si-OMeTPA HTL.(3)Two π-conjugated small-molecule HTL materials BDT-TPA-sTh and BDT-TPA-sTPA containing a benzo[1,2-b:4,5-b’]dithiophene(BDT)and TPA derivative branches respectively,were successfully synthesized.X-ray crystallography of BDT-TPA-sTh based 2-ethylhexyl-thienyl group as side chain showed that the BDT-TPA-sTh molecule simultaneously exhibits parallel-displaced π-π intermolecular interactions and S-π weak-bond interactions.And these supramolecular interactions can enhance the molecular stacking and improve the hole mobility.In addition,we also found that the marginal solubility of BDT-TPA-sTh in perovskite solution enabled inverse diffusion into the perovskite film and the diffused BDT-TPA-sTh would further passivate the uncoordinated Pb2+ ion defects by Lewis-base S-atoms.When employing the dopant-free BDT-TPA-sTh as HTL,the p-i-n planar pero-SCs showed a champion PCE of 20.5%.The pero-SCs with blade-coated BDT-TPA-sTh HTL achieved a 15.30%PCE for a 1-cm2 modularized device.(4)Based on TPA derivate as the donor unit,pyrazine with different side chains as the acceptor unit,D-A type organic small molecule HTLs X2 and X3 were designed and synthesized.X-ray crystallography of X2 showed that supramolecular interactions in X2 molecule can enhance molecular stacking,thus improving the hole mobility.Simultaneously,the introduction of cyano groups in X2 can not only lower the highest occupied molecular orbital(HOMO)energy level to match well with the valence band of perovskite but also efficiently passivate the uncoordinated Pb2+ ion defects.Finally,the p-i-n planar pero-SCs based on X2 as HTL displayed a PCE of 20.16%and robust stability.The corresponding pero-SCs with bladed X2 HTL showed a high PCE of 19.56%.