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

TL;DR

This paper investigates the fabrication, doping levels, and operational stability of lead-halide perovskite pn-junction solar cells, questioning the impact of doping densities on device performance and junction integrity.

Contribution

It provides detailed measurements of doping densities in perovskite pn-junctions and analyzes their implications for device electrostatics and photovoltaic efficiency.

Findings

Doping densities vary from 10^{12} to 8×10^{12} cm^{-3} for n-type layers.

Doping densities are potentially insufficient to alter electrostatic potential significantly.

The study raises questions about the stability and benefits of pn-junctions in 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 $N_D = 10^{12} cm^{-3}$ 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.