Differential Response of the Photoluminescence and Photocurrent of Polycrystalline CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ to the Exposure to Oxygen and Nitrogen

Because of their excellent photoelectric properties, organic–inorganic metal halide perovskites (MHPs), such as methylammonium lead triiodide, CH3NH3PbI3 (MAPbI3), and methylammonium lead tribromide, CH3NH3PbBr3 (MAPbBr3), are of great interest for the emerging MHPs-based photovoltaic technology. Despite extensive research efforts focused on physicochemical aspects of both MAPbI3 and MAPbBr3, the impact of environmental extremes, including various gaseous media, on their photoelectric properties remains poorly understood. In this context, here, the MHPs-based gas-sensing elements were grown by one-step solution process on the outer surface of cylindrical in shape quartz substrates with diameters varying in the range of 80–1100 μm. The elongated cylinder-shaped geometry and high surface-to-volume ratios of the thus-prepared deposits revealed advantageous for designing miniature, light-transparent gas-flow chambers and made it possible to investigate the photoluminescence (PL) and photocurrent (PC) responses of both MHPs exposed to the precisely controlled recurrent flow of either O2 or N2. In addition, we could also collect the PL responses for the deposits of MAPbI3 and MAPbBr3, positioned side-by-side close to each other and therefore simultaneously exposed to identical environmental conditions. Specifically, we found that under exposure to O2 the PL responses of MAPbI3 and MAPbBr3 were markedly opposite; i.e., the PL decreased for MAPbI3, whereas it increased for MAPbBr3. In contrast, under the exposure to N2, the PL of MAPbI3 increased, while it decreased for MAPbBr3. A considerably differential behavior was also found for the PC responses. In particular, under recurrent exposures to both gaseous media, the PL and PC responses of MAPbBr3 correlated, whereas for MAPbI3 they anticorrelated. In conclusion, the distinctly opposite PL and PC responses of polycrystalline deposits of MAPbI3 and MAPbBr3 to O2 and N2 reported herein point to markedly contrasting properties of the surface carrier traps and defects for these two MHPs. This study also evidences that a side-by-side arrangement of elongated cylindrically shaped substrates coated with two different MHPs, due to their differential responses to exposure to O2 or N2, can function as a simple differential gas detector.