Approaching Charge Separation Efficiency to Unity without Charge Recombination

Improving the efficiency of charge separation (CS) and charge transport (CT) is essential for almost all optoelectronic applications, yet its maximization remains a big challenge. Here we propose a conceptual strategy to achieve CS efficiency close to unity and simultaneously avoid charge recombination (CR) during CT in a ferroelectric polar-discontinuity (PD) superlattice structure, as demonstrated in ${({\mathrm{BaTiO}}_{3})}_{m}/{({\mathrm{BiFeO}}_{3})}_{n}$, which is fundamentally different from the existing mechanisms. The competition of interfacial dipole and ferroelectric PD induces opposite band bending in ${\mathrm{BiFeO}}_{3}$ and ${\mathrm{BaTiO}}_{3}$ sublattices. Consequently, the photoexcited electrons ($e$) and holes ($h$) in individual sublattices move forward to the opposite interfaces forming electrically isolated $e$ and $h$ channels, leading to a CS efficiency close to unity. Importantly, the spatial isolation of conduction channels in ${({\mathrm{BaTiO}}_{3})}_{m}/{({\mathrm{BiFeO}}_{3})}_{n}$ enable suppression of CR during CT, thus realizing a unique band diagram for spatially orthogonal CS and CT. Remarkably, ${({\mathrm{BaTiO}}_{3})}_{m}/{({\mathrm{BiFeO}}_{3})}_{n}$ can maintain a high photocurrent and large band gap simultaneously. Our results provide a fascinating illumination for designing artificial heterostructures toward ideal CS and CT in optoelectronic applications.