  Cui et al. describe the fabrication and characterization of planar
pn-junction solar cells based on lead-halide perovskites. The doping densities
measured using Hall effect measurements vary from $N_D = 10^{12} cm^{-3}$ to
$8\times 10^{12} cm^{-3}$ for the solution-processed n-type layer and $N_A =
8\times 10^9 cm^{-3}$ for the evaporated p-type layer. While these devices
outperform their counterparts, that are supposedly un-doped, the results raise
three important questions: (i) Are the reported doping densities high enough to
change the electrostatic potential distribution in the device from that for the
un-doped ones, (ii) are the doping densities high enough for the pn-junction to
remain intact under typical photovoltaic operation conditions and (iii) is a
pn-junction beneficial for photovoltaic performance given the typical
properties of lead-halide perovskites.
