(Invited) Design of Perovskites for High-Performance Electronics and Optoelectronics

Abstract

The success of lead halide perovskites as active materials in optoelectronic technologies is often associated with the unique properties of their optical excitations. Specifically, the photo-generated excitons in perovskites are responsible for the large absorption coefficients close to their band gap, reaching as high as 105 cm-1. Due to the advent of nanotechnology, perovskite materials can be readily fabricated into nanoscale configurations with different dimensionalities, and more importantly, the corresponding excitonic effects could be further enhanced. On the other hand, at length scales down to the nanoscale regime, surface features as well as quantum confinement effects, become dominant in regulating the advanced material properties of perovskite materials. [1, 2] In recent years, our group focused on the synthesis and characterization of metal halide perovskites with different forms, ranging from bulk film, microplate, and nanosheet, to nanowire. The corresponding physical properties and device applications were also systematically studied based on their widely tunable dimensionality, morphologies, and compositions.For perovskite bulk films, surface defects and bulk structural order significantly affect device performance. Through optimizing processing techniques, self-assemble quasi-2D perovskite films with graded phase distribution were successfully prepared by our group. [3] Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained, which is further employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibited impressive performance with responsivity up to 444 mA/W and ultrashort response time down to 52 µs. In addition, to probe the intrinsic material properties of crystalline perovskites, freestanding MAPbI3 nanosheets, and lead-free Cs3Sb2I9 microplates were fabricated by two-step chemical vapor deposition method, in which excellent optoelectronic performance (e.g., responsively of MAPbI3 nanosheet is measured to be 40 A/W) together with ultra-fast response speed (down to 58 µs) and superior thermal stability were obtained. [4, 5]For nanostructured perovskites, understanding the dimensional features and their impact on the materials and devices is becoming increasingly important. For the first time, we reported the direct vapor-liquid-solid growth of single-crystalline all-inorganic lead halide perovskite (i.e., CsPbX3; X = Cl, Br, or I) NWs using Sn as catalyst seeds. [6] These NWs exhibited high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors based on individual CsPbX3 NWs were also fabricated to show the impressive carrier mobility of 3.05 cm2/Vs, being higher than other all-inorganic perovskite devices. After that, the Au catalyst seeds were used to avoid the Sn-related impurity doping, by which lower dark current and higher detectivity were achieved in Au-seeded CsPbI3 NWs. Besides, the realization of high-mobility CsPbBr3 NW devices is reported via a simple surface charge transfer doping strategy. [7] After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs. All these results provide important guidelines for the further improvement of these perovskite nanostructures for practical utilization.