Preparation Of Highly Stable Perovskite Ordered Structure Films Based On An Ion Confinement Strategy

Organic-inorganic hybrid perovskite solar cells（PSCs）have attracted extensive research attention due to their outstanding optoelectronic properties.In the past ten years,its power conversion efficiency（PCE）has increased from 3.8%in 2009 to the current 25.7%.Chemical vapor deposition（CVD）technology is conducive to the scalable development of perovskite with the advantages of precise control of film thickness and being solvent-free.There have been challenges for PSCs in the form of long-term stability,because of the low vacancy formation energy,organic-inorganic hybrid perovskites suffer from serious ion migration issue.And this ion migration will lead to a series of stability problems,which can hardly be addressed by encapsulation.Currently,interface modification methods have been widely used to enhance the long-term stability of PSCs,which were mainly achieved by inserting ion-blocking layers into the interface between perovskite layer and charge transport layer.These strategies could effectively address the stability issues caused by the interfacial ion diffusion between perovskite and charge transport layer.However,the ion migration inside the perovskite layer could still be a knotty problem,which is difficult to be solved through surface modification.Herein,we propose a new strategy based on a vapor-solid reaction method to obtain a"perovskite/interlayer/perovskite"film by inserting an interlayer into the perovskite layer,thus mitigating the internal ion migration in perovskite.The research contents of this paper are as follows:（1）The thickness of Pb I₂film and reaction atmosphere during the vapor-solid reaction were optimized,and the best-quality perovskite films were obtained at a Pb I₂thickness of 400 nm and a mass ratio of 4:1 between FAI and FACl,respectively.The optimal device PCE were 16.42%and 17.61%,respectively.Based on the solvent-free advantage of CVD method,the strategy of hierarchically preparing double-layer perovskite was adopted.The fusion of two layers of perovskite resulted in a final device PCE of 17.17%.（2）Based on hierarchical preparation,graphene oxide（GO）was introduced into the middle of the two-layer perovskite.The composition ratio of GO dispersant was first explored,and the optimal balance of GO dispersibility and perovskite erosiveness was finally achieved when the hydro-alcohol volume ratio was 1:1.Depositing GO by ultrasonic spray coating,two-dimensional（2D）scale coverage was achieved on the perovskite surface,and a 3D/2D/3D sandwich-perovskite ordered structure was successfully constructed.The GO interlayer could successfully mitigate the ion migration in the as-prepared perovskite/GO/perovskite.The best device with a GO interlayer achieved an PCE of 16.71%,which maitained 85%of its initial PCE under 96 hours of continuous illumination,and showed no obvious fatigue under 10illumination/darkness cycling test.Replacing GO with another 2D material,tungsten disulfide（WS₂）,we found that it did not have the same ion blocking effect as GO.（3）Polymers such as PMMA and PTAA were used as interlayer materials to investigate their effects on perovskite ion migration and device performance.PMMA had a strong ability to block ion diffusion but caused a significant loss of device performance.PTAA had a relatively small loss of device performance,but with a weak inhibitory effect on ion migration.The two materials were not balanced on both sides.