Synthesis Of Functionalized Fullerene Derivatives And Study Of Their Effects On The Stability Of Perovskite Solar Cells

Halide perovskite materials have broad application prospects in the field of solar cells due to their excellent optical and electrical properties,such as long carrier diffusion length and lifetime,and strong visible light absorption capacity.The highest certified photoelectric conversion efficiency（PCEs）of perovskite solar cells（PSCs）has reached 25.7%,which has the advantages of low production cost,abundant sources,and solution preparation.However,perovskite solar cells also have problems such as poor long-term stability,serious hysteresis,difficult control of perovskite layer grain quality,and low interlayer charge transfer efficiency.These problems seriously affect the commercial development of perovskite solar cells.To solve these problems,three kinds of fullerene derivatives were designed and synthesized in this paper,which was used as interface modification materials or additive materials in perovskite solar cells.To improve the stability of perovskite solar cell devices,improve the charge transfer efficiency between devices and improve the morphology of perovskite crystals,the following three parts were carried out:A novel fullerene dimer derivative(2C₆₀-Bphen)was designed and synthesized to improve interlayer charge transport,improve the quality of perovskite films,and improve device stability.The structure of the product was confirmed by the characterization test.The 2C₆₀-Bphen was spin-coated on the surface of the tin oxide electron transport material as an interface modification material between the electron transport layer and the perovskite layer.The results show that the photoelectric conversion efficiency of the corresponding device is increased from 19.65%to 20.24%after the modification of 2C₆₀-Bphen with a concentration of 0.5 mg m L^-1 between the tin oxide and the perovskite layer.After 500 h storage under ambient conditions,the efficiency of the standard device remains at 74%of the initial efficiency,and the device modified by 2C₆₀-Bphen is 85%.The analysis shows that the use of 2C₆₀-Bphen to modify tin oxide can increase the contact angle of the tin oxide surface so that the perovskite film has a larger grain size and fewer defects,which is more conducive to resisting the erosion of water and oxygen.At the same time,the pyridine nitrogen（N）in the 2C₆₀-Bphen structure can passivate the lead iodide defects and improve the stability of the device by reducing the decomposition rate of the perovskite film.To regulate the morphology of the perovskite layer,passivate the defects of the perovskite layer and improve the stability of devices in a humid environment,two fluorinated fullerene derivatives(3F-C₆₀ and 7F-C₆₀)were designed and synthesized.As an additive material,it is added to the perovskite solution precursor of the inverted perovskite solar cell.When the concentration of 7F-C₆₀ and 3F-C₆₀ is 0.05 wt%,the best efficiency is achieved,and the device efficiency is increased from 19.19%to 19.54%and 20.34%,respectively.The devices with standard,3F-C_60,and 7F-C₆₀ can maintain85%,88%,and 91%of the initial efficiency after being placed for 500 h at 85%humidity.The analysis shows that the fullerene additive provides heterogeneous nucleation sites for the formation of perovskite films,which is beneficial to obtain perovskite films with larger grain sizes,more uniform distribution,and smaller grain boundaries.The C=O in 3F-C₆₀ and 7F-C₆₀ can passivate the uncoordinated Pb²⁺in the perovskite film,and the fluorocarbon chain can form hydrogen bonds with methylamine.This double-site passivation can reduce the defect state density of the device and inhibit ion migration.In addition,the introduction of hydrophobic fluorocarbon chains improves the hydrophobicity of the perovskite film,thereby improving the stability of the device in a humid environment.To passivate the surface defects of titanium oxide,reduce the interface energy level barrier,improve the quality of perovskite film,and improve the stability of the device,a cyano fullerene derivative(C₆₀-CN)was synthesized by reference.C₆₀-CN was used as a modification material between the titanium oxide layer and the perovskite layer in the upright perovskite solar cell.The results showed that the photoelectric conversion efficiency of the corresponding device was increased from 17.05%to 18.60%after the titanium oxide was modified by C₆₀-CN with a concentration of 0.75 mg m L^-1.After500 h storage under ambient conditions,the efficiency of the standard device remains at 74%of the initial efficiency,and the device modified by C₆₀-CN is 85%.It is confirmed by cyclic voltammetry that the energy level of C₆₀-CN matches with perovskite（MAPb I₃）,which can reduce the interlayer energy level barrier and improve the interlayer charge transfer efficiency.The modification of C₆₀-CN can passivate the oxygen vacancies on the surface of titanium oxide and reduce the density of defect states of the device.In addition,the modification of C₆₀-CN can increase the hydrophobic angle of the titanium oxide layer,which is conducive to the formation of perovskite crystals,and obtain high-quality perovskite films with larger grain sizes and smaller grain boundaries.