To boost the efficiency of perovskite as a light source for optoelectronics, researchers coupled lead halide perovskite nanocrystals to a nanophotonic cavity. The research team drop cast perovskite nanocrystals in a toluene solution onto a silicon nitride (SiN) cavity. They then excited the device with a pulsed laser, which led to photon emission from the nanocrystals. Room-temperature time-resolved lifetime measurements demonstrated an average spontaneous emission rate enhancement of 2.9 for perovskite nanocrystals within the cavity, as compared to those located on the unpatterned surfaces, indicating a nearly threefold increase in the photon emitting efficiency within the cavity. The coupled device between the photonic crystal nanobeam cavity and perovskite nanocrystals, which overlays with the cavity mode profile. The arrows indicate that the excitation and generated signal are coupled in and out of the device vertically. Courtesy of Zhili Yang, University of Maryland. The use of solutions to make colloidal quantum emitters differs from the fabrication of epitaxial materials, a widely used process that involves growing crystalline overlayers on an existing substrate. According to researchers, it is easier to directly deposit colloidal nanocrystals using solvents on different kinds of wafers. Attempts to emit light with epitaxial materials have generally fallen short of efficiently covering the visible light spectrum, with the wavelength range in the blue-green being particularly problematic. The coupled device demonstrated by the research team from the University of Maryland and ETH Zürich exhibited emission centered at 510 nm in the green. “The large challenge with this method, however, is that you have to find a very optimized concentration (density) of the crystals on the surface of the cavity,” researcher Zhili Yang said. “It can't be too condensed or else it will be detrimental to the cavity and might lead to nonconformity.” The researchers believe that solution-processable lead trihalide perovskite semiconductors could provide an alternative in optoelectronic applications to epitaxial materials that require complex growth capabilities to synthesize. Perovskites exhibit a small Stokes shift, high charge carrier mobility and large absorption coefficient. According to researchers, these features could enable high-performance photovoltaic devices, light-emitting diodes and light sources for efficient lasers. Beyond photovoltaics, perovskites could serve as an efficient emitter and gain material for optoelectronic applications. “Our work shows that it is possible to enhance the spontaneous emission of colloidal perovskite nanocrystals using a photonic cavity,” Yang said. “Our results provide a path toward compact on-chip light sources with reduced energy consumption and size.” The research was published in Applied Physics Letters (doi: 10.1063/1.5000248).