Construction Of Planar π-conjugated Materials And Their Application In Passivation Of Perovskite Defects

Perovskite solar cells（PSCs）have attracted extensive attention of researchers due to their small exciton binding energy,excellent light absorption capability,and simple and low-cost fabrication methods.At present,although the efficiency of PSCs has exceeded 25.5%,the defects（surface defects,grain boundary defects）caused by the preparation of perovskite films have become the biggest bottleneck restricting the further improvement of their efficiency.Therefore,it is of great research significance to reduce the defect density of perovskite films to improve the efficiency and stability of battery devices.In this thesis,small organic molecules（benzothiophene,carbazole,phenothiazine,perylene tetracarboxylic acid diimide）was used as the host materials,and planarπ-conjugated functional materials were constructed by solvothermal method and co-precipitation method.The passivation mechanism of perovskite film defects（surface defects,grain boundary defects）were studied.The main research contents are as follows:1.Aiming at the surface defects of perovskite films,this work proposes to use benzothiophene,carbazole,and phenothiazine as carbon sources to prepare carbon dots withπ-conjugated structure that can effectively passivate the surface defects of perovskite films by solvothermal method.The results show that carbon dots is formed by the cleavage and recombination of benzothiophene molecules through solvothermal treatment.In addition,the emergence of a new functional group C-O-C during the solvothermal process elevates its HOMO energy level,making it more compatible with the valence band of perovskite for holeing transport.However,under the same conditions,because the carbazole and phenothiazine molecules did not reach the energy of breaking bonds,the breaking of chemical bonds and the formation of carbon dots did not occur,its HOMO energy level changes less and mismatched with the valence band of perovskite.More importantly,due to the appearance of S=O and C=O bonds in the benzothiophene carbon dots structure,the surface defects of perovskite are effectively passivated and the recombination of carriers is reduced,hereby improving the performance of the device.Using the above products as holeing transport materials,compared with the devices prepared by carbazole products（11.65%）and phenothiazine products（9.50%）without new functional groups,the benzothiophene carbon dot modified devices achieve 13.22%photoelectric conversion efficiency.This method provides the possibility to develop excellent defect state passivation materials from a new perspective.2.Aiming at the grain boundary defects of perovskite thin films,based on the confined microenvironment of hydrotalcite,this work uses a co-precipitation method to construct N,N-bis（propionic acid）-perylene-3,4,9,10-tetracarboxylate acid diimide（PDI）assembly material.The results show that,compared with PDI monomer,PDI assembly has a higherπ-πconjugated system,which is beneficial to its transfer and separation of photogenerated carriers.More importantly,the C=O bond in the PDI assembly can interact with Pb²⁺,which can effectively passivate the grain boundary defects of the perovskite film and reduce the trap-assisted recombination,thereby improving the efficiency and stability of the device.Based on the above design,the photoelectric conversion efficiency of PSCs devices assisted by PDI assemblies up to 14.17%were achieved by utilizing theπ-πconjugation of PDI assemblies and the passivation of grain boundary defects in perovskite films.This work not only broadens the application prospects of the assembly,but also provides an effective way to develop low-cost,high-performance optoelectronic devices.