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All inorganic lead-based perovskites containing bromine-iodine alloys, such as CsPbIBr2, have arisen as one of the most attractive candidates for absorber layers in solar cells. That said, there remains a large gap when it comes to film and crystal quality between the inorganic and hybrid perovskites. In this work, antisolvent engineering is employed as a simple and reproducible method for improving CsPbIBr2 thin films. We found that both the antisolvent used and the conditions under which it was applied have a measurable impact on both the quality and stability of the final product. We arrived at this conclusion by characterising the samples using scanning electron microscopy, X-ray diffraction, UV–visible and photoluminescence measurements, as well as employing a novel system to quantify stability. Our findings, and the application of our novel method for quantifying stability, demonstrate the ability to significantly enhance CsPbIBr2 samples, produced via a static one-step spin coating method, by applying isopropanol 10 s after commencing the spin programme. The antisolvent quenched CsPbIBr2 films demonstrate both improved crystallinity and an extended lifespan.

In this work CsPbIBr2 is doped with rubidium, where up to 12% of caesium atoms are replaced with those of rubidium. The obtained Cs1-xRbxPbIBr2, x= (0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12), films were characterized by X-ray diffraction (XRD), the scanning electron microscope (SEM), photo-luminescence (PL) and UVvisible spectroscopy. The integration of Rb + ions into the lattice leads to a detectable change in optoelectronic and morphological structure. Substituting 6% of caesium atoms yields the best results, eliminating pinholes, and elevating crystallite size and absorption coefficient by 116% and 125%, respectively. Other novel observations, of particular interest, include a slight increase in band-gap energy from 2.1eV to 2.14eV, and a decrease in stability. Over a period of 15 days, where temperature and relative humidity kept at 23°C and 20% respectively, a larger amount of degradation was seen to take place as rubidium content was increased. Therefore, the doping of CsPbIBr2 with rubidium is most useful in the case where specifically film and crystal quality are desired to be targeted.

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