Study On Solvent Engineering To Improve The Performance Of CsPbIBr₂ Perovskite Solar Cells And Corresponding Mechanism

Traditional fossil fuels have drawbacks such as non-renewability and environmental pollution,driving people to urgently seek clean and sustainable new energy sources.Solar energy,as a natural,pollution-free,and inexhaustible source of energy,has received wide attention.Among them,crystalline silicon solar cells were the earliest researched and have been commercially applied.However,due to barriers in raw materials and processing technology,the development of crystalline silicon solar cells has been greatly hindered.As a rising star,new halide perovskite solar cells have rapidly developed and achieved a certified efficiency of25.7%,mainly due to their flexible and inexpensive manufacturing process,suitable energy band structure,high light absorption coefficient,large carrier mobility,and diffusion length.However,traditional organic-inorganic hybrid perovskites contain unstable organic components in humid and hot environments,which can cause perovskite decomposition and device performance degradation.Inorganic Cs Pb I_3-xBr_x perovskites,which replace organic ion groups with Cs⁺,are considered one of the materials with great potential to improve device stability in perovskite optoelectronic devices due to their excellent thermal stability.Common hole transport layer materials in new perovskite solar cells often use expensive organic small molecules or polymers,whose organic components can also affect the long-term stability of perovskite devices.From the perspective of improving device stability and reducing costs,this study selects Cs Pb IBr₂ with appropriate bandgap and stability as the research object based on laboratory preliminary research.Carbon is used as an electrode to replace traditional noble metal electrodes and hole transport layers,and the influence of solvent engineering on perovskite crystallization kinetics is carefully examined.High-quality Cs Pb IBr₂films are obtained and the underlying mechanism is analyzed in combination with theoretical calculation.It is then applied to carbon-based device structures without hole layers,achieving over 13%PCE while having excellent stability.The main research contents are as follows:（1）The quality of Cs Pb IBr₂ thin films was improved by dropwise addition of three different anti-solvents（chlorobenzene,isopropanol,methanol）using a one-step spin-coating method.Phase analysis of the films before and after annealing revealed that the Cs Pb IBr₂ films treated with methanol exhibited the fastest nucleation promotion effect before annealing and achieved the highest crystallinity after annealing.First-principles analysis showed that the driving force for the anti-solvent extraction of Dimethyl sulfoxide（DMSO）comes from the polarity difference,while infrared detection and theory jointly revealed that the anti-solvent triggers supersaturation in the wet film by interacting with S=O in DMSO.The addition of anti-solvents also effectively increased the carrier lifetime of the thin films.Finally,carbon-based Cs Pb IBr₂devices without hole transport layers prepared by adding methanol solution obtained a highest PCE of 5.55%and a Voc of 1.17 V.（2）By introducing Cs I into methanol solution to regulate the nucleation process and passivate crystal defects,the concentration of Cs I methanol solution was first optimized.Thanks to the joint action of both,on the one hand,it prevented the formation of non-photoactiveδ-phase Cs Pb IBr₂,facilitating the formation of pore-free dense film morphology.At a concentration of 30 mg/L,the device achieved the best PCE value.The addition of Cs I also helped to produce the Cs-rich phase Cs4Pb I_6-xBr_x,which significantly inhibited non-radiative recombination in the film while passivating internal defects.On the basis of the optimal concentration of 30 mg/L,the dropwise amount of Cs I methanol solution was further optimized.When the Cs I dropwise amount was 300μL,the corresponding device achieved a fill factor of 76.9%and a PCE of 13.4%.Exploring the effects of different substances on perovskite crystallization by replacing Cs I with MAI（CH₃NH₃I）,KI,and Cs Br,none of the three substances showed feasibility in improving device performance due to their respective reasons.KI easily triggered the formation ofδ-phase perovskite due to the small radius of K⁺;while MAI rapidly evaporated and destroyed the original crystal morphology during annealing at 280°C;Cs Br led to an increase in bandgap due to the increase of Br^-.The optimal performance device treated with Cs I methanol solution was tested for stability under an indoor environment with a relative humidity of about 30%.After storage for nearly 500 hours,it still maintained over 85%of the initial efficiency,demonstrating excellent stability under moisture and light conditions.（3）To directly regulate the crystallization kinetics of perovskite and achieve large grain size and dense film morphology,a homogenous perovskite-induced annealing strategy（abbreviated as homogenous induction strategy）was introduced.Compared with conventional one-step and two-step annealing methods,Cs Pb IBr₂ films prepared by the homogenous induction strategy showed excellent crystal quality and preferential growth of（h00,h=1 and 2）planes.The carrier extraction process of Cs Pb IBr₂films prepared by this strategy became more rapid and efficient.Combining first-principles calculations and experimental analysis,the effects of the homogenous induction strategy on Cs Pb IBr₂ films were mainly from two aspects:1)the evaporation rate and residual time of the solvent DMSO were greatly extended,which helped to dissolve small crystals and form larger grain sizes with more sufficient growth time;2)the top Cs Pb IBr₂ provided a seed for perovskite growth from top to bottom,and the（h00）plane with the lowest surface energy guided the growth of perovskite in the wet film below,while the preferential growth of the（h00）plane also contributed to the efficient separation and transport of carriers in the thin film.The best PCE of the corresponding device increased by44%compared with traditional annealing schemes.