Observing the stability evolution of β-DMAxCs1-xPbI2Br through precursor incubation

Previous research had demonstrated that the addition of HI into the mixture solution of CsI and PbI2 with DMF could be beneficial to the formation of DMAxCs1-xPbI3 (DMA = dimethylammonium, (CH3)2NH2+) with improved stability and efficiency. In this paper, we found that the proper incubation duration of the mixed precursor is crucial to the stability of the perovskite film of DMAxCs1-xPbI2Br and the efficiency of the corresponding solar cell. Meanwhile, the amount of CsI in the precursor has been modified to adjust the ratio between Cs and DMA in perovskite film, which is further adjusted through the incubation duration of the precursor solution. Experimental results demonstrate that, besides the bandgap of the final perovskite film, both efficiency and stability are dependent on the addition amount of CsI and incubation duration of the precursor. X-ray diffraction has been adopted to understand the stability variation of different perovskite films. Finally, the bare perovskite films fabricated from precursors with Cs/Pb ratios of 0.7 and 0.8 after 24 h incubation keep stable for more than 10 h respectively against the high moisture condition of 60% relative humidity. That is a great improvement as compared with the film from the previously reported protocol of precursor, which will be quickly decomposed within 1 h in such a high moisture environment. The carbon electrode based solar cell fabricated from a precursor with Cs/Pb of 0.8 after 24 h incubation exhibits the highest power conversion efficiency of 8.5% on average. Consequently, the study in this paper would be helpful in understanding the stability and efficiency of the solar cell based on DMAxCs1-xPbI2Br.