Perovskite Whispering Gallery Mode Resonators

Abstract

Silica-based whispering gallery mode resonators are well documented for their ability to support ultra-high quality factor resonant modes. However, silica is not known for its optoelectronic properties and this limits the reach of these devices. Recently, perovskite materials have been posited as excellent photonic and optoelectronic materials as they can possess tunable bandgaps, extreme nonlinearities, and low losses. Perovskite photonics is a nascent field and owing to the solution processable nature of the materials, which make ‘post-processing’ difficult, perovskite whispering gallery mode resonators are an unexplored research topic. In this project, we combine the ultra-high Q-factor of silica whispering gallery mode resonators with the exciting photonic properties of perovskites. Hybrid resonators were made by growing high purity methyl-ammonium lead bromide, MAPbBr3, perovskite inside a thin-walled silica micro-capillary. An Finite-Difference Time-Domain (FDTD) model-based investigation was undertaken to predict the silica-perovskite resonator’s modal response. These studies suggest that a wall thickness of less than 10 µm is required to elicit light-matter interaction with the perovskite. In order to characterise the resonators, a bespoke whispering gallery mode characterisation system was developed with a fast scanning speed of 100 nms−1 and high spectral resolution of 1 pm. This was used to characterise the MAPbBr3 resonators which were measured to have a high quality factor of Q = 6.1×105 and a free spectral range of FSR = 9.148nm; results that matched well with the numerical study. Furthermore, it was possible to investigate ion-migration, a characteristic of perovskites, which manifests as blue spectral shift. Ion diffusion relaxation was determined to have a decay constant of τave = 2.98±0.3 minutes, which is in good agreement with corresponding optoelectronic measurements in the literature. This result clearly demonstrates the hybrid nature of the devices and that the light has access to the optoelectronic properties of the perovskite. This work extends the field of photonics by opening up a new avenue to explore and exploit the superlative optoelectronic properties of the perovskite materials family.