During the fabrication of perovskite solar cells,the perovskite layer changes from yellowish to dark brown in color on annealing. However ,when i fabricated at first dark brown color appears for few seconds and again changes into yellowish color.How can this problem be solved and why it is happening?Peovskite solution was made by takiing equimolar solutions of methyl ammonium hydrochloride and lead iodide in 1,2-dichlorobenzene and was fabricated in humidity less than 40%
Hi Arup,
It is highly likely that the sample was overheated and decomposed during annealing. Perovskite material processes very low thermal stability. It will quickly decompose at a high temperature (>150 C, ~ melting temp. of MAI or MACl), especially with the help of humidity air. Depending on the purpose of your experiment, you may want to try a lower annealing temp. (80 - 100 C for equimolar precursor), a high molar concentration (~1 M) , and a short annealing time (10 to 30 min).
Our paper could be helpful:
https://www.researchgate.net/publication/277900036_Impact_of_Processing_Temperature_and_Composition_on_the_Formation_of_Methylammonium_Lead_Iodide_Perovskites
Article Impact of Processing Temperature and Composition on the Form...
Structure has been distorted due to annealing so decrease the annealing temperature as well as time.