| The development of efficient hole transport materials is an effective way to improve the photovoltaic performance and stability of perovskite solar cells.Spiro-OMe TAD is currently widely studied as a reference hole transport material in perovskite solar cell devices,the 3D spirobifluorene core in its structure provides a larger steric hindrance,which effectively prevents the formation of large crystalline domains when spin-coated into a film,but it faces many problems such as low intrinsic hole mobility and poor self-stability.In order to further clarify the relationship between the molecular structure and its own performance and the performance of the corresponding device,many Spiro-OMe TAD analogues have been continuously developed and utilized.In this paper,three groups of small organic molecules HTMs were synthesized by different planar regularity and electrondonating ability of the central core structure and combinded with different electron-rich terminal aromatic amine units.The relationship between the molecular structure and the hole transport performance of materials,the morphology of thin films and the stability of molecules themselves was investigated.The corresponding perovskite solar cell devices were prepared and the effects of different hole transport materials on the device performance were studied.The details are as follows:1.Using trimethyl-substituted triphenylene rigid planar disc-shaped molecules as the core,connecting different methoxyaniline end groups to obtain compounds TPDPA and TPTPA,and exploring their basic photoelectric properties,it was found that both compounds have more than 100 The large Stokes shift of nm guarantees its good hole extraction ability.In addition,the introduction of methyl groups on the core of triphenylene not only improves the molecular HOMO energy level,but also increases the steric hindrance and reduces the molecular plane.It ensures high hole mobility and improves the film formation and hydrophobicity of the molecule(water contact angle greater than 80°);finally,two hole transport materials are used for the preparation of PSCs without doping The results show that the TPTPA-based device achieves a higher photoelectric conversion efficiency of 14.68%.It can be seen that the trimethyl substituted triphenylene core with a positioning resistance effect can be used as an ideal core unit for hole transport materials.2.Select SFX as the core unit,and retain the 3D core of the spirocyclic hole-transporting material.By introducing fluorine atoms and adjusting the substitution position of fluorine,three small molecules(SFX-o-2F,SFX-m-2F and SFX-p-2F)hole-transporting materials,it was found that the position of fluorine substitution had little effect on the optical and electrochemical properties of the resulting small molecules,but it led to their very different photovoltaic performance.The performance of PSC based on SFX-m-2F with a fluorine substituent in the meta position(18.86%)is superior to others,and is based on Spiro-OMe TAD’s equipment(18.98%)is basically the same.The performance improvement of SFX-m-2F is maybe related to its better morphology,more effective hole transport and extraction characteristics at the perovskite/hole transport material interface,thus achieving the optimal JSC(22.64 m A cm-2)At the FF(71.85%)level.So it can be seen that the material performance can be adjusted through fluorination engineering to improve the efficiency of the corresponding device.Controlling the position of fluorine substitution in the spiral ring connection unit may be to develop more economical and efficient holes one of the effective strategies for transferring materials.3.We have researched and expanded the end groups of the hole-transporting material molecules.In Chapter 4,we used the highly sterically hindered spirobifluorene as the core and selected the isomer N-phenyl-1-Naphthylamine and N-phenyl-2-naphthylamine were used as terminal groups to obtain compounds Spiro-α-NNA and Spiro-β-NNA,respectively.The influence of terminal group steric hindrance on material properties and device performance was explored.It is found that the 2-substituted naphthalene end group has less steric hindrance from the adjacent benzene ring than the1-substituted naphthalene end group,and thus has better stretchability,which helps it form a good film morphology and promote excitation.For sub-extraction and transmission,the performance of the corresponding device is relatively better.The best PCE of the PSC based on Spiro-β-4NNA is15.32%,which is lower than the photovoltaic efficiency of the device using Spiro-OMe TAD as the hole transport material.Its PCE is 18.44 %;but it is worth noting that under the same conditions,the stability of the device corresponding to the target hole transport material is better than that of the device using Spiro-OMe TAD as the hole transport layer.The photovoltaic performance of the perovskite solar cell based on Spiro-β-4NNA can retain 85% of its initial performance after being stored for 1200 hours in a dark condition with a humidity of 30%,while the efficiency of the device corresponding to Spiro-OMe TAD decreases by more than 20%,which shows that naphthylamine end group can be used as a substituent for improving the stability of the device to prepare the hole transport material of perovskite solar cell. |
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