Stoichiometry-driven structural superiority and crossover from intrinsic band-like to hopping transport in mixed...

Understanding intrinsic charge transport properties of perovskites is pivotal for unlocking their full potential in optoelectronics. Yet progress is fundamentally constrained by extrinsic charge disorder stemming from ion migration and trap states, particularly in compositionally complex hybrid systems. Here, we overcome this limitation through "trap-free" MA_1-xFA_xPbI₃ crystals (x = 0-1), leveraging stoichiometric precision to achieve structural perfection, peaking at x = 0.52. MA_0.48FA_0.52PbI₃ crystals demonstrate minimal lattice disorder (FWHM = 0.013°), an ultralow trap density (1.1 × 10¹² cm^-3), and maximal mechanical robustness and carrier lifetimes, governed by a near-ideal Goldschmidt tolerance factor (0.998) and suppressed ion migration. This lattice perfection enables intrinsic band-like transport behavior, yielding n-type FET mobilities of 2.4 cm² V^-1 s^-1 at RT, which increase to 52.1 cm² V^-1 s^-1 at 80 K. A stoichiometry-driven transition to phonon-assisted hopping conduction is identified at x = 0.8. By isolating stoichiometry-dependent transport mechanisms, we address longstanding ambiguities in MA_1-xFA_xPbI₃ transport physics and deliver a crystal engineering framework for high-performance photoelectronic devices.