Vertically Aligned Carbon Nanotubes as Electrodes in Perovskite Single Crystal Light Emitting Electrochemical Cells
Abstract
We demonstrate that single crystals of methylammonium lead bromide (MAPbBr3) could be grown directly on vertically aligned carbon nanotube (VACNT) forests. The fast-growing MAPbBr3 single crystals engulfed the protogenetic inclusions in the form of individual CNTs, thus resulting in a threedimensionally enlarged photosensitive interface. Photodetector devices were obtained, detecting low light intensities ( 20 nW) from UV range to 550 nm. Moreover, bright green electroluminescence of the MAPbBr3 single crystals, using symmetrical VACNT electrodes, was observed at room temperature for both polarities. The electroluminescence spectra and light intensity was recorded from room temperature to cryogenic temperatures (20 K). The underlying mechanism behind the light emission is the well documented ion migration. In fact charged ions or vacancies inside the perovskite, drift under an external electric field accumulating at the cathode and anode, forming a p-i-n heterojunction structure. These characteristics have a strong similarity with the operational mechanism of polymer light- emitting electrochemical cells (LECs), especially the device structure and the involvement of mobile ions for efficient electroluminescence. This reveals that vertically aligned CNTs can be used as electrodes in operationally stable perovskite- based optoelectronic devices and can serve as a versatile platform for future selective electrode development.
