Semiconductive Polarity Control in Halide Perovskites through Defect Chemistry and Interface Engineering

The remarkable rise of metal halide perovskite photovoltaics and optoelectronics has revealed semiconductive polarity as a central yet insufficiently understood determinant of device performance and stability. The soft ionic-covalent lattice of halide perovskites hosts highly mobile ions and low-formation-energy defects that spontaneously self-dope and dynamically shift the Fermi level. This unique defect-lattice interplay profoundly affects band alignment, quasi-Fermi-level splitting, interfacial recombination, and ultimately the attainable open-circuit voltage. In this review, we establish a hierarchical framework for polarity regulation spanning bulk defect thermodynamics, compositional tuning, additive coordination chemistry, and interfacial electronic design. We first elucidate how lattice geometry, orbital hybridization, and intrinsic defect equilibria dictate bulk carrier density and Fermi-level position. We then discuss how targeted A/B/X-site substitution, alloying strategies, and stoichiometric control modulate defect landscapes and stabilize desired electronic character. Based on these principles, we highlight how interfacial polarity engineering, including charge-transfer interlayers and selective-contact design, enables continuity of quasi-Fermi levels and minimizes nonradiative losses at both p- and n-type contacts. These insights unify defect physics and interfacial electrostatics, guiding polarity-balanced, defect-regulated perovskite optoelectronics, and highlighting opportunities in electrostatic modulation, heterovalent doping, surface reconstruction, and polarity engineering for perovskite solar cells.