With increased air and thermal stability and an ever-growing device efficiency, all-inorganic halide perovskites are currently receiving great interest within the solar cell community. Although thermal stability is considerably improved by removal of the volatile organic components [1,2], structures such as CsPbI₃ and CsPbI₂Br still suffer from a performance-damaging phase transition from the cubic, photoactive perovskite α-phase, to a wide bandgap photo-inactive but thermodynamically favoured δ-phase, leading to issues for commercialisation [3,4]. To assist in the prevention of this phase change, good film and crystal quality, with minimal defects is vital. An approach to ensure this high absorber quality is by employing dopants during the film formation. Dopants are also used to increase the carrier lifetimes resulting in improved device performance [5,6].

In recent literature, chloride-based dopants are becoming a popular choice. However, studies remain focussed on device performance and bulk film characterisation, with little attention paid to grain-level crystallisation. In addition, there is little to confirm whether the dopant is proportionally incorporated into the film, or present in the final film at all [7-10].

In this present work, detailed electron backscatter diffraction (EBSD) mapping, X-Ray diffraction (XRD), Cathodoluminescence (CL) and Wavelength dispersive x-ray (WDX) spectroscopy measurements have been carried out to unravel the chloride-dopant-induced film improvement of all-inorganic CsPbI₂Br absorbers. The EBSD mapping is used to elucidate the influence of a PbCl₂ dopant on the crystallisation of CsPbI₂Br, and the effects of differing concentrations on the film. XRD measurements are used to confirm the observations and confirm lack of PbCl₂ starting material in the final film. CL spectra and maps reveal the peak shift brought on by the chloride dopant, suggesting a material composition change which alters the bandgap of the perovskite. WDX spectroscopy is used to detect chloride traces within the film, confirming proportional chlorine incorporation. Some comparisons are made with a CuCl₂ dopant to further reveal the role of the cation in stabilising the perovskite phase.

This work provides vital insights into the roles that chloride dopants have in the formation of all-inorganic perovskite absorbers leading to performance enhancement.