Unravelling the chloride dopant induced film improvement in all-inorganic perovskite absorbers

CsPbI₂Br perovskite material has been the focus of much recent research, thanks to its improved stability over CsPbI₃, useful bandgap of 1.9 eV and enhanced thermal stability over hybrid perovskite materials with volatile organic components. It has great potential for both single junction solar cells for indoor applications, and implementation in tandem cells. However, moisture stability has remained an issue. In order to overcome this roadblock towards commercialisation, metal chloride dopants have been widely investigated to improve film quality and reduce damage from humidity. Most of the studies report that the metal cation in the dopant plays a greater role in the improvement of the film properties than the chloride anions, which are thought to be removed during annealing in some studies. The majority of the research to date on this topic has focussed on investigating device performance and bulk film characteristics, with limited attention paid to grain-level crystallinity and whether the dopant is proportionally incorporated into the film. In the present work, cathodoluminescence (CL) and electron backscatter diffraction (EBSD) are utilised to investigate the effects of a lead chloride dopant, both on emission and crystal structure at a grain level, with the findings supported by X-ray diffraction (XRD). Confirmation of proportional incorporation of the dopant into the final prepared films is provided by wavelength dispersive X-ray (WDX) spectroscopy. This work provides valuable insight into the impact chloride dopants have on all-inorganic perovskite absorbers, helping to influence future dopant strategies.