Band-like Transport with Hall Mobility >70 cm2 V–1 s–1 in Stoichiometric Perovskite Crystals via Ion Confinement and Strain Relaxation

Abstract Despite substantial progress in optoelectronic applications, lead–halide perovskites remain underperforming in field-effect transistors (FETs) due to multiphase instability, ion migration, and grain boundary scattering. Here, a dual-ion co-incorporation strategy was applied to CsxFA1–xPbI3–yBry single crystals. By systematically mapping a phase stability diagram, we pinpoint an optimal stoichiometry of Cs0.1FA0.9PbI2.7Br0.3 that integrates phase stability engineering with atomic-level ion confinement. Structural analysis reveals that 10% Cs+/Br– co-incorporation induces strain-relaxed lattice contraction (−1.23% along the a-axis relative to FAPbI3) and reinforces Pb–I bonds via octahedral distortion. This yields superior crystallinity (FWHM = 0.04°) and reduced I– migration, thereby enabling the investigation of FET and gated Hall effect carrier mobilities as functions of temperature. Consequently, champion two-terminal FET devices exhibit an electron mobility of 25.1 cm2 V–1 s–1 at room temperature, which increases to 126 cm2 V–1 s–1 at 120 K. Furthermore, high-resolution four-terminal measurements on a single crystal quantify and correct for contact-resistance effects, validating the relationship: Hall mobility (μHall) > linear regime mobility (μlin) > saturation regime mobility (μsat) with values of 89, 79.2, and 71.6 cm2 V–1 s–1, respectively. These findings collectively elucidate intrinsic band-like electron transport behavior in lead–halide perovskite single crystals, distinguishing it from hopping transport in organic semiconductors. By achieving a defect-minimized lattice, this compositional engineering paradigm overcomes the mobility bottleneck in perovskite FETs, facilitating the transition from photoelectronic applications to FET integration.