Ligand-assisted ion exchange enabled ultralong compositionally graded perovskite nanowires

The bandgap engineering of halide perovskites via ion exchange has attracted extensive attention in recent years. However, the composition tuning at the microscale is still challenging due to complicated procedures for achieving spatial resolution. Herein, we report a facile and efficient approach for fabricating ultralong, compositionally graded CsPbBr3 − 3xI3x nanowires (NWs). By incorporating a ligand barrier onto the NW surface, the ion exchange is confined only to both ends of the NWs, leading to a compositional gradient extending over tens of micrometers along individual NWs. Further study shows that the funnel-like energy band structure facilitates the transport of photo-generated carriers, as evidenced by the excellent spectral and optoelectronic performance of the gradient NW device. Such ligand-assisted, spatially resolved band engineering is conducted at ambient conditions without additional process of nanofabrication or micro-manipulation, which is suitable for integration into miniaturized optoelectronic devices.