Intrinsic doping limitations in inorganic lead halide perovskites

Area of Science:

• Materials Science
• Solid-State Physics
• Semiconductor Physics

Background:

• Inorganic halide perovskites (HP's) like CsPbX₃ are emerging semiconductors with high photovoltaic efficiencies.
• HP's exhibit an unusual asymmetry in doping, predominantly showing p-type behavior with low free carrier concentrations.
• This doping limitation raises questions about whether it's due to process issues or intrinsic material properties.

Purpose of the Study:

• To investigate the fundamental design principles (DPs) governing ideal doping in inorganic halide perovskites.
• To identify which DPs are violated in HP's, explaining their doping limitations and asymmetry.
• To determine if doping challenges are intrinsic or due to insufficient process optimization.

Main Methods:

• Application of density functional doping theory to study three fundamental design principles for ideal doping.
• Analysis of thermodynamic transition levels and Fermi level pinning energies for donor and acceptor dopants.
• Evaluation of doping-induced shifts in equilibrium Fermi energy for n-type and p-type doping.

Main Results:

• While some shallow-level dopants satisfy the first design principle (DP-(i)) in Br- and Cl-based HP's, DP-(ii) is only met for holes.
• The third design principle (DP-(iii)) fails for both holes and electrons across various HP compositions.
• DP-(ii) and DP-(iii) violations are identified as the primary bottlenecks, particularly for n-type doping in Iodide HP's.

Conclusions:

• The study suggests an intrinsic physical mechanism limits doping in inorganic halide perovskites.
• Violations of specific design principles, especially concerning Fermi level pinning and doping-induced shifts, explain doping asymmetry and limitations.
• These findings highlight fundamental challenges in achieving efficient n-type doping in HP semiconductors.