## 4 Discussion and Conclusions
At the B and X sites, when a high concentration of dopant is incorporated the valence or conduction band can be altered with electronic contributions of the dopant. This work shows that doping of perovskite is linked to improved photovoltaic properties such as enhanced carrier dynamics, improved PL, and bandgap tuning, which all increase the VOC. Table 2 depicts the effects of doping on perovskite properties, focused on zinc and several other dopants. The property regulation as measured (or speculated) by the authors is mentioned in combination with the voltage enhancements. For every dopant, an increase in VOC is measured. Many authors report increased grains and/or enhanced crystallinity as the mechanism behind this. Some report strain relaxation or chemical bond enhancement. Almost none report the reduced density of defects. So, we conclude that the doping effects in literature are rarely directly linked to reduced defect density. Contradictions in literature show that more research should be conducted to correlate crystallization to the density of defects. We do note that some recent computational studies have shown that strain relaxation and chemical bond enhancement can lead to increased defect formation energies. Because of this, we identify the two mechanisms as attractive approaches to rationally reduce native defects in perovskite. However, we emphasize that future research should, also here, focus on finding the relation between perovskite doping and the reduction of defect density, more specifically the precise regulation of which point \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Add.** & **[\%]** & **Location** & **Perovskite** & **Property Regulation** & **VOC (ud)** & **VOC (d)** & **Enh. d/ud** & **Year (ref)** \\ \hline Alkali & 5 & A-site; interstitial & MAPbI3 & Enlarge grain size; & & & & 2018 \\  & & & interstitial & enhance crystallinity & - & - & - & [48] \\ Zn(II) \({}^{1}\) & 11 & B-site & CSaI3 & Widen band gap (by 0.7 eV); & - & - & - & [49] \\  & & & & & & & & \\  & & & & & & & & \\ ZnI\({}_{2}\) & 1 & B-site & MAPbI3\(\times\)Clx & & uniform crystals; & 1.05 & 1.08 & 1.03 & [35] \\  & & & & & & & & \\  & & & & & & & & \\ ZnCl\({}_{2}\) & 3 & & & MAPbI3 & improved surface & 1.05 & 1.09 & 1.04 & [46] \\  & & & & & & & & \\  & & & & & & & & \\ ZnI\({}_{2}\) & 1-2 & B-Site & FAPb0.5 SnO5I3 & & & & & & \\  & & & & & & & & \\ ZnCl\({}_{2}\) & 0.1 & B-site & MAPbI3 & Enlarged grain size & 1.00 & 1.06 & 1.06 & [30] \\  & & & & & & & & \\ CdI\({}_{2}\) & 5 & B-site & CsMAFPb & Strain relaxation; & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ PbCl\({}_{2}\) & 5 & X-site & CsMAFPb & suppressed vacancy & 1.157 & 1.160 & 1.00 & [33] \\  & & & & & & & & \\  & & & & & & & & \\ NaF & 0.1 & Surface & Cs0.05 FAMAPb & Chemical bond & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ Al-acac\({}_{3}\) & 0.15 & Surface & MAPbI3 & Enhanced crystallinity; & 1.01 & 1.06 & 1.05 & [29] \\  & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The effects of doping on perovskite properties. Dopants are reported as the additive (= Add. ), the content (%) is the amount that improved photoluminescence or efficiencies the most, location of incorporation is given when experimentally/computationally determined, property regulations are mostly experimentally measured, the VOC is given for the undoped and doped perovskite (ud = undoped, d = doped), together with the enhancement factor (d/ud). The year is the year the article is published, reference is given. \({}^{1}\) marks a computational study. It has to be noted that various device architectures and perovskite compositions are compared. The property regulation and enhancement is however a generally observed effect. defects become less (or more) predominant. For example, what the doping effect is on \(\rm V_{I}\) and \(\rm I_{i}\) defects, which were identified as important point defects in Section 2. We highlight here the recent paper of [PERSON] et al.