RESUMEN
The dynamic crystal lattice of halide perovskites facilitates the coupled transport of ions and electrons, offering innovative concepts in semiconductor iontronic devices that surpass solar cell applications. However, a comprehensive understanding of the intricacies of coupled ionic and electronic transport at the microscale remains ambiguous, owing to the inhomogeneity in ploy-crystalline perovskite thin films. In this work, we employed one-dimensional (1D) single-crystalline CsPbBr3 nanowires (NWs) to investigate the electric field induced ionic transport. Upon poling by an external bias, the previously uniform NW exhibits highly anisotropic ionic transport, which is identified as the origin of the giant switchable photovoltaic effect by spatially resolved scanning photocurrent microscopy. The subsequent ultrafast scanning photoluminescence (PL) microscopy measurements demonstrate significant localization of photocarriers near one terminal of the device, which is attributed to the accumulation of halogen vacancies. In addition, thanks to the enhancement of the local electric field, the poled device shows a 10-fold increase of photoresponse speed. Our findings favor the scale-down of perovskite devices to the submicrometer scale, extending their applications in self-powered iontronic and optoelectronic devices.
RESUMEN
The coupled ionic and electronic transport in halide perovskites opens up new possibilities for semiconductor iontronic devices beyond solar cells. Nevertheless, the fundamental understanding of ionic behavior at the microscale remains vague, largely because of the inhomogeneity in polycrystalline thin films. Here, we show that the ion dynamics in single-crystalline perovskite nanoplates (NPs) are significantly different and that an external bias may induce highly anisotropic ionic transport in the NPs, thereby leading to a greatly enhanced local electric field. Using modified scanning photocurrent microscopy (SPCM), the origin of the photocurrent is pinpointed to the cathode region of the NP device, where subsequent energy dispersive spectroscopy (EDS) characterization confirms a large accumulation of halogen vacancies. In addition, the Kelvin probe force microscopy (KPFM) measurement demonstrates a strong built-in electric field within a submicron length near the cathode, which alters the local electronic structure for efficient photo carrier separation. Such field-induced ionic behavior deepens the understanding of ion dynamics in perovskites and promotes scale-down of perovskite micro- and nanoiontronic and ion-optoelectronic devices.
RESUMEN
Anion-exchange in halide perovskites provides a unique pathway of bandgap engineering for fabricating heterojunctions in low-cost photovoltaics and optoelectronics. However, it remains challenging to achieve robust and sharp perovskite heterojunctions, due to the spontaneous anion interdiffusion across the heterojunction in 3D perovskites. Here, it is shown that the anionic behavior in 1D perovskites is fundamentally different, that the anion exchange can readily drive an indirect-to-direct bandgap phase transition in CsPbI3 nanowires (NWs) and greatly lower the phase transition temperature. In addition, the heterojunction created by phase transition is epitaxial in nature, and its chemical composition can be precisely controlled upon postannealing. Further study of the phase transition dynamics reveals a threshold-dominating anion exchange mechanism in these 1D NWs rather than the gradient-dominating mechanism in 3D systems. The results provide important insights into the ionic behavior in halide perovskites, which is beneficial for applications in solar cells, light-emitting diodes (LEDs), and other semiconductor devices.
