Synthesis Of Zinc Phthalocyanine Hole Transporting Materials And Application In Perovskite Solar Cells

In recent years,organic-metal halide perovskite solar cells(PSCs)have shown great promise in photovoltaic research due to their high efficiency,low cost,and ease of processing.Its power conversion efficiency(PCE)increased quickly from the initial 3.8% to 23.7%.The hole transporting material plays an important role in transporting holes,protecting the perovskite layer,blocking electron reflow,and promoting the crystallization of perovskite in the PSCs.These conventional HTMs,such as spiroOMeTAD,have been suffered from several disadvantages of high synthesis cost,low thermal and chemical stability or low conductivity.In addition,the commonly used HTMs require the addition of organic dopants such as LiTFSI and t-BP.Hygroscopicity and deliquescence of these additives accelerating degradation of device performance.Therefore,the explore of low-cost,dopant-free HTMs is crucial for PSCs technology in the future commercial applications.Phthalocyanine(PCs)have 18-? electron aromatic heterocyclic ring system formed by the connection of four isomeric groups,usually studied as a p-type semiconductor in solar cells and organic thin-film transistors in the near-infrared region.Because of its higher hole mobility,flexibility,outstanding chemical/thermal stability and cheaper,it has received great attention as hole transporting materials in perovskite solar cells.The disadvantages such as strong aggregation,difficult to dissolve and purify restrict the development of phthalocyanine materials.In this paper,three kinds of phthalocyanine derivatives with different substituents of phthalocyanine as core were designed and synthesized.The thermal stability,photophysical and electrochemical properties of the materials were systematically studied and applyed it in perovskite solar cells.First,a tetra-methoxyltriphenylamine substituted zinc phthalocyanine(OTPAZnPc)has been synthesized and utilized as a dopant-free HTM for PSCs.The introduction of 4,4'-dimethoxytriphenylamine side chains on ZnPc possesses a wonderful solubility in various solvents,such as dichloromethane,chlorobenzene,and N,N-dimethylformamide.The methoxy functional group in the hole transporting molecule acts as a Lewis base for defect healing by forming a Lewis adduct having uncoordinated ions,thereby attenuating defects in the perovskite and improving the interface to obtain better performance.The optimized devices achieved a power conversion efficiency of 16.23% under AM1.5 G standard conditions.What's more,due to the hydrophobic nature of the OTPA-ZnPc,the solar cells remained about 80% of its initial efficiency after 720 h of storage in ambient air with a humidity of approximately 45% without encapsulation,which is obvious better stability than the spiro-OMeTAD devices.Our results indicate that solution-processable OTPA-ZnPc is an encouraging dopant-free hole transporting material in perovskite solar cells.In order to further study the influence of other electron-rich groups to the molecular structure and the performance of perovskite solar cells,we have introduced thiophene groups based on the previous work to obtain a new type of inexpensive hole transport material OTPAT-ZnPc.Thiophene as an electron-rich group can increase the HOMO level,and after introducing the thiophene group,the HOMO level of OTPATZnPc is increased by 0.1 eV compared to OTPA-ZnPc.The OTPAT-ZnPc molecule contains longer side arms with a two-dimensional extension system.The phenylthiophene unit facilitates defect deactivation at the HTM/perovskite interface by Pb-S interaction,promoting charge delocalization and mobility of the hole transport material molecules.The synthesized material was applied to the perovskite solar cells,and an impressive PCE of 16.58% was obtained without dopant.Although small molecule phthalocyanine phthalocyanine derivatives have the advantages of easy synthesis,high hole mobility,and the like.However,in solution,phthalocyanine is very easy to form dimers and polymers.The high molecular polymer has the advantages of being easy to produce,and the molecular chain is soft and controllable.Therefore,based on this,we designed and synthesized a phthalocyanine functional polymer to combine the advantages of phthalocyanine and polymer.The side chain phthalonitrile-containing polymer PMADCE was first synthesized by an "active" /controlled radical polymerization method.The polymer had a number average molecular weight Mn of 12212 g/moL and a molecular weight distribution index PDI of 1.38.The zinc phthalocyanine functionalized polymer PMADCE-ZnPc was then obtained by a post polymerization modification method.The phthalocyanine polymer combines the advantages of a polymer and a phthalocyanine molecule,has good film forming properties,a suitable HOMO level,and good thermal stability.PMADCEZnPc was used as hole transporting materials in perovskite solar cells,and a higher PCE of 13.61% was obtained without dopant.It is particularly noteworthy that the device still has 95% efficient efficiency after 30 days.