Organolead halide perovskites MAPbX₃ (MA = CH₃NH₃⁺; X = Cl^-, Br^-, I^-) have emerged as attractive materials for photovoltaic and optoelectronic devices. In perovskite-based devices, long-distance carrier diffusion is essential to high device performance. Diffusion lengths up to micrometers have been reported in both polycrystalline and single-crystal perovskites. In addition to utilizing the intrinsic transport properties of perovskites, the versatile wet-chemistry synthesis and processing of perovskites allow further enhancement of carrier transportation through nanoscale engineering.

To achieve this goal, the research group led by Prof. JIN Shengye in Dalian Institute of Chemical Physics developed a “solid-to-solid” halide exchange reaction and successfully synthesized halide-gradient MAPbBr_xI_3-x perovskite Nanowires (NWs). The NWs comprise a bromide-rich region (high-bandgap) at one side of the wire and an iodide-rich region (low-bandgap) on the other side. So that the energy difference between two sides can drive the unidirectional transportation of charge carriers.

Long-Distance Charge Carrier Funneling in Perovskite Nanowires Enabled by Built-in Halide Gradient (Image by TIAN Wenming and JIN Shengye)

By using time-resolved Photoluminescence (PL) imaging and kinetics measurements, researchers observed several-micrometers unidirectional charge carrier transportation from bromide-rich region to the iodide-rich region. In comparison with the intrinsic carrier diffusion, the carrier transportation driven by bandgap energy gradient exhibited superior ability in directional carrier transfer. It makes these NWs ideal candidates for applications in long-distance photon-energy delivery and nanoscale optoelectronics.

The related results were published in Journal of the American Chemical Society. This work is financially supported by Ministry of Science and Technology (2016YFA0200602) and National Nature Science Foundation of China (21473192).