Hong-Hua Fang received the Ph.D. degrees in electronics from Jilin University in 2013. His PH. D. thesis focused on ultrafast dynamics and nonlinear optics of functional organic single crystals for solid-state laser applications. After that, he joined the Photophysics and OptoElectronics group of the Zernike Institute for Advanced Materials, University of Groningen (The Netherlands). He specializes in femtosecond laser methods and time- resolved optical microscopy to explore the rich physics of nanostructured and quantum- confined materials and gain new insight into energy transport mechanisms in the devices for next-generation renewable energy technologies.

In this work, we find that the optoelectronic properties of methylammonium-lead tribromide (MAPbBr3) single crystals exhibit extreme sensitivity to environmental gases. We show evidence that the surface trap state density can be reversibly controlled by the physisorption of oxygen and water molecules, leading to a modulation of the photoluminescence intensity modulation of by over two orders of magnitude. By time-resolved single- and two-photon photoluminescence spectra, we demonstrate an unusually low surface recombination velocity, which is 3 orders of magnitude smaller than the one of detector-grade silicon crystals. In addition, a modulation of the transport properties in the single crystal devices is presented. Our findings highlight the importance of environmental conditions on the investigation and fabrication of high-quality, perovskite-based devices, and provide a new potential application of these materials for detecting oxygen and water vapor.