Low-temperature Atomic Layer Deposited Films For Encapsulation Of Perovskite Solar Cells

Atomic layer deposition is a thin film fabricationtechnology based on chemical reactions between gas-phase precursors and groups on the surface of substrates.The precursors are dosed in an alternating manner so that the product is chemically adsorbed on the substrates layer by layer at the atomic level.The films prepared by atomic layer deposition,therefore,have the advantages of being dense,pinhole-free,conformal,highly controllable in thickness and components.In recent years,encapsulation films prepared by atomic layer deposition have become one of the important methods to solve the problem of stability of perovskite solar cells.However,the metal halide perovskite structure shows extremely low pyrolysis temperature and chemical stability.Excessive temperatures or the use of active precursors in the encapsulation process of perovskite solar cells usually cause damage,which significantly reduces device performance.This paper mainly focuses on the research of perovskite solar cell thin-film encapsulation based on low-temperature atomic layer deposition.It starts from the reaction mechanism and steric effect in low-temperature atomic layer deposition to improve the films'barrier performance.Finally,based on the preparation of high-quality low-temperature films,a new encapsulation structure is designed for metal halide perovskite solar cells with inferior stability.Plasma-enhanced atomic layer deposition consequently is applied for the first time in thin-film encapsulation of perovskite solar cells.This novel strategy successfully solved the problem of preparing high-performance encapsulation films for perovskite solar cells,and it is expected to significantly improve the stability of perovskite solar cells in the future.The research contents and results of this thesis mainly include the following aspects:1?Based on the in-situ quadrupole mass spectrometer monitoring,the reaction paths of trimethylaluminum and active precursors?oxygen plasma and ozone?at low temperature are summarized,and a reaction path between trimethylaluminum and oxygen plasma that oxygen atomics inserted into the carbon-hydrogen bonds is determined.It is believed that the difference in reaction paths is the main reason for the difference in film properties.2?In-situ quartz crystal balances were used to characterize the self-limiting properties of atomic layer deposition.Correctly,the standard deviation coefficient of the mass increase per cycle is used to represent the degree of dispersion of the growth amount per cycle,thus characterizing the stability of self-limiting growth.Based on this,the relationship between the self-limiting characteristic of atomic layer deposition and the properties of the grown thin films was studied.3?Investigate the effects of low kinetic on film properties in low-temperature atomic layer deposition.By controlling the pulse mode,pulse time and purge time to control the precursor partial pressure and exposure time,the effects of molecular motion on transient steric hindrance,saturation adsorption and physical adsorption were studied.It was found that the multiple short pulse method significantly reduces the low-temperature atomic layer deposition film density while reducing half of the purge time required for the adsorption equilibrium.4?Perovskite solar cells were encapsulated without damage using low-activity precursor ethylene glycol.It also acted as a protective layer in the plasma-enhanced atomic layer deposition encapsulation process.Unreacted groups remained in the film fabricated by the low-temperature molecular layer deposition,which consumed active plasma that penetrates the film,thereby avoiding damage to the solar cells.The molecular layer deposition/plasma-enhanced atomic layer deposition composite structure shown a water vapor transmission rate as high as 1.3×10^-5g/m²/day.After encapsulation,the devices maintained 99.91%of the original efficiency,achieving high-performance and non-damaging encapsulation of the perovskite solar cells.