Data used for 'A Critical Assessment of the Use of Excess Lead Iodide in Lead Halide Perovskite Solar Cells'.

1. X-ray diffractogram and SEM images of a MAPbI3 film with an excess of PbI2 illustrating how PbI2 can be detected. 2. X-ray diffractograms and SEM images of MAPbI3 films with varying excesses of PbI2. The peak intensities from the X-ray data and white areas in SEM images are used to study the incorporation of PbI2 into MAPbI3 films. 3. Device parameters for FTO/TiO2/MAPbI3/Spiro/Au devices for varying amounts of PbI2 excess. 4. External quantum efficiency and photoluminescense excitation data for MAPbI3 devices with carying amounts of PbI2 excess. 5. Stability measurements for FTO/TiO2/MAPbI3/Spiro/Au devices with stoichiometric and excess amount of PbI2. 6. Schematic of the proposed influence PbI2 has an device performance and stability. SI. Full X-ray diffractograms of MAPbI3 films with excess PbI2 and average FWHM of the peaks in these diffractograms. SEM images of MAPbI3 films with excess PbI2. Calculation of PbI2 surface layer thickness for 5 mol% excess. Detailed device parameters and calculation of Voc from measured PLQE values on MAPbI3 films. Photoluminescence data for stoichiometric and excess PbI2 MAPbI3 films. Device and stability measurements for stoichiometric and excess PbI2 CsFAPbI3 devices. SEM and XRD of a film before and after illumination showing photolysis of PbI2.