Study On Doping And Solvent Engineering Of Hole Transport Layer In Perovskite Solar Cells

Perovskite solar cells（PSCs）with high efficiency,easy preparation and low cost have attracted great interest from researchers in the recent years.The electron transport layer,perovskite absorption layer,hole transport layer and electrodes of PSCs are mainly prepared by layer-by-layer deposition.Among them,the hole transport layer plays an important role in the construction of efficient and stable PSCs.Therefore,it is scientifically important and valuable to carry out the study of hole transport layer to promote the performance improvement and commercialization of PSCs.In this thesis,a detailed study of the hole transport layer of PSCs is carried out,which specifically includes novel hole dopants and solvent engineering of the hole transport layer.The research contents and findings are as follows:A new hole dopant,Li-CYCLO,was developed and used to dope the hole transport material PTAA by modulating the anion unit of the classical hole dopant lithium bis（trifluoromethanesulfonyl）imide（Li-TFSI）from linear to cyclic,and the results showed that the Li-CYCLO doped PTAA has higher electrical conductivity,more suitable highest occupied molecular orbital（HOMO）energy level,and better interfacial charge transport performance,which contributes to the development of high-performance PSCs.The PSCs based on Li-CYCLO doped PTAA obtained the best photovoltaic conversion efficiency（PCE）of 22.23%,which is higher than that of the reference device with Li-TFSI doped PTAA（21.61%）.In addition,the anion modulation,which results in lower hygroscopic properties of Li-CYCLO,and the corresponding cells exhibit more excellent environmental stability.The efficiency of the unencapsulated cell maintained 70%of the initial value after aging in an air environment（relative humidity（RH）:50-85%,room temperature（RT））for 40 days,and the reference device maintained 49%of the initial PCE.An organic Lewis acid dopant Zn-FP with excellent doping performance,fluorine-containing hydrophobic properties and high migration barrier was developed to replace Li-TFSI and used to dope the hole transport material PTAA.20.34%PCE was obtained for PSCs based on Zn-FP-doped PTAA.Stability studies showed that Zn-FP-based cells obtained excellent operational stability and environmental stability:the unencapsulated cell maintained more than 90%of the initial efficiency after 1000 hours of continuous operation under N₂ atmosphere and a standard simulated solar intensity,and the PSCs did not exhibit J-V hysteresis throughout the aging process;the unencapsulated PSCs maintained more than 89%of the initial to efficiency after 40 days of aging in an air environment（RH:50-85%,RT）.The results of time-of-flight secondary ion mass spectrometry（TOF-SIMS）and density functional theory（DFT）calculations indicate that Zn-FP is difficult to migrate inside the device during operation and Zn-FP can effectively passivate the surface defects of perovskite,thus enhancing the cell’s stability in light operation.In addition,the fluorine-containing hydrophobic property of Zn-FP helps to enhance the environmental stability of the cell.A green solvent,anisole,was developed to replace chlorobenzene（CB）as the solvent for the hole transport material PTAA.Fourier transform infrared spectroscopy（FTIR）results showed intermolecular interactions between anisole and PTAA,which help to promote the hole transport.The effects of anisole on the interfacial charge transport properties and morphology of PTAA were analyzed in depth by combining fluorescence spectroscopy and atomic force microscopy.Finally,the dopant-free PTAA PSCs based on anisole as the solvent obtained 17.35%PCE and showed excellent reproducibility,which was higher than that of the reference device based on chlorobenzene as solvent for PTAA（15.37%）.In addition,the PSCs based on anisole dopant-free PTAA also exhibited excellent environmental stability,maintaining 82%of the initial value after 40 days of aging in atmospheric environment（RH:50-85%,RT）.