I am making 2-step perovskite solar cells and after my first step of PbI2 coating (600mg PbI2 in DMSO/DMF) and annealing (70C for 30min), a white cloudy layer appears on top of the PbI2 layer (shown in the picture) and the final solar cells has very low FF and Voc. Does anyone know what might cause this problem? Thanks in advance!
Dear Melody,
If the PbI2 solution is pure and also the substrate is clean and from a material which can not react with the solution, then it may be that PbI2 is partly decomposed by long heating and light. By scanning the web i found that PbI2 can be decomposed by light.
So, you have to revise all these causes. But i would expect it is the long heating or light exposure that may cause decomposition of the PbI2.
Best wishes.
Best wishes
Hello Sir,
May i Know the molarity of PbI2 solution you are using?
Also, do the cloudy patches appear after dipping in MAI solution?
It seems bottom layer is not completly annealed or its surface is not enough smooth. Please do the AFM and c-AFM to know about roughness and local current variation in bottom layer.
Hello,
This cloudy layer could be due to surface roughness of the perovskite. Conversion from PbI2 to perovskite is tricky and final film quality depends on both PbI2 layer quality and conversion process. You can use small amount of 2-methoxyethanol additive to your organic (MAI) solution.
For more detail information: Article Improved Morphology and Efficiency of n-i-p Planar Perovskit...
Good Luck.
It also depends on your underlayer on what you are spin coating the PbI2. If you have compact/meso TiO2 and you are seeing loudy layer on top of PbI2 then maybe your TiO2 underlayers are too thick. However, in your provided picture it seems the cloudy layer is on the total perovskite layer which can be co-related to many factors such as dipping time, temparature of the PbI2 substrate during the dipping in MAI soulution.
In that case please check the surface morphology and surface roughness of SnO2 layer first and try to obtain SnO2 films with lowest roughness. If you can co-relate these factors with the clouds on top of the Perovskite film, you might have a clear understanding of the device performance.
Good Luck!!
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