Requirements for functional pn-homojunctions in lead-halide perovskite solar cells

Abstract

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 $N_D=10^{12}c{m}^{-3}$ to $8\times 10^{12}c{m}^{-3}$ for the solution-processed n-type layer and $N_A=8\times 10^{9}c{m}^{-3}$ 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.