## 3 Doping of Perovskites with Zinc(II)
This composition can also be used in a solvent free grinding method, giving easy access to perovskite pellets. The final product featured protective alkyl tails that stabilized the structure. The photoluminescence of the thin film material was studied with confocal microscopy, directly deposited on indium tin oxide (ITO), leading to charge injection (see Figure 4). The confocal microscopy indicates a dense network of similarly shaped hexagonal and pentagonal perovskite microcrystals, with \(\sim\)500 nm dimensions. The ratio (lifetime/intensity) accentuates the special character of the grain boundaries, that show properties different from the bulk (or the centers of the crystals). These materials remain black without substantial loss of sharp XRD features even after 1440 h at ambient (Dutch) indoor conditions. In 2017, [PERSON] et al. reported [15] the partial replacement of Pb\({}^{2+}\) by Zn\({}^{2+}\) in MAPbI\({}_{3}\) perovskites. The emphasis was on the effects of zinc doping (with ZnI\({}_{2}\)) on morphology, optical, electronic and photovoltaic performance. The zinc substituted perovskite layers, here denoted as MA(Pb:Zn)I\({}_{3}\), were prepared through solution processing. It appears that no chloride components were used. Soon it  
Figure 4: Confocal microscopy image of FA\({}_{0.85}\)MA\({}_{0.15}\)Pb\({}_{0.975}\)Zn\({}_{0.025}\)I\({}_{2.85}\)Br\({}_{0.15}\)-[CPACI] obtained by dividing the photoluminescence lifetime-image by the intensity-image (INT) thereby accentuating the grain boundary areas, as processed with Image-J (lifetime/INT, fire-color coding). The network of light blue lines highlights the special grain boundary effect, which is in-fact induced by charge recombination interaction with the ITO surface (not observed on quartz). Pink spots are characterized by a very low emission intensity and long emissive lifetime. Image dimension is \(20\times 20\)\(\upmu\)m. See also Reference [16]. This picture is best viewed on-screen. Figure 3: Formation of films and pellets from their starting components. Decreasing ratio CPACI: FA/MA, annealing or grinding steps are indicated. The crystalline units form a larger well-organized and protected final product. See Reference [16] for more information on this composition. was clear that the addition of small quantities of Zn strongly enhances the charge carrier collection efficiency of the cell leading to a higher overall efficiency. It was witnessed that the carrier lifetime of the device increased linearly with the increasing Zn content up to 15%. Other important enhancements were the morphology and crystallinity of the film. The presence of Zn enlarges the grain size and reduces the grain boundary surface. Nonradiative recombination takes place at these grain boundary surface and as a consequence the presence of zinc reduces the non-radiative recombination having an advantageous effect on efficiency. Because morphology and coverage of the perovskite film is of such essence, [PERSON] et al. tried various preparation conditions to create a densely packed perovskite film with large grains and a highly covered surface. As shown in the first entries of Figure 5a-c, undoped perovskite features small grains and therefore a high grain boundary area. When the Zn concentration is raised the grain size increases, which suggest that Zn has a profound effect on the nucleation and subsequent crystal growth processes that occur during the fabrication processes. When the structure is doped with 15% Zn the material contains many pinholes that can cause low-resistant leakage pathways. The search for optimal Zn concentrations and annealing temperatures yielded a film with a 5% Zn content annealed for 10 min at 120 \({}^{\circ}\)C. Large grains are visible and no pinholes are present in this film. By studying the XRD spectrum shown in Figure 6 it became clear that pure tetragonal perovskite was formed and that there were no impure phases, such as PbI\({}_{2}\), present.