Synergistic design of p-type transparent conductors: dual-regulation strategy in Sn2+/Pb2+-based bromides.

Transparent conductors (TCs) are essential functional components in optoelectronics. However, the scarcity of p-type materials that simultaneously achieve high optical transparency and superior electrical conductivity poses a critical research frontier and a persistent challenge in semiconductor engineering. Addressing this limitation requires a strategic elevation of the valence band maximum (VBM) to mitigate hole localization and optimize optoelectronic performance. This study introduces an innovative dual-regulation paradigm: (i) cationic modulation via Sn2+ or Pb2+ antibonding states substantially upshifts the valence band and enhances hole mobility, and (ii) anionic substitution with non-oxygen bromine (Br-) ligands concurrently reduces the hole effective mass and suppresses localization. This synergy improves both carrier mobility and dopability. Through integrated first-principles calculations and swarm-intelligence structure exploration, we designed six novel ternary alkaline-earth metal bromides: ASn2Br6 (A = Ca, Sr or Ba), CaPb2Br6 and Ca2BBr6 (B = Sn or Pb). These materials show wide optical bandgaps (>3.3 eV) that ensure visible-range transparency, and strong Sn-5s/Br-4p (or Pb-6s/Br-4p) antibonding interactions at the valence band edge that favor p-type defect formation. In particular, the AB2Br6 subfamily exhibits moderate (1.36 to 2.06 m0) compatible with charge transport, highlighting their potential for appreciable p-type conductivity. However, the relatively heavy of Ca2SnBr6 and Ca2PbBr6 (4.29 and 3.94 m0, respectively) prevents the successful decoupling of the conflict between high transparency and high conductivity. Non-equilibrium growth is imperative to kinetically bypass compensating Br vacancies (VBr) and surpass solubility limits. This work establishes Sn2+/Pb2+-based bromides as next-generation p-type TC candidates and provides fundamental insights into designing high-performance optoelectronic materials through electronic structure engineering.