CsPbBr3-ZrO2 Janus-Type II Heterostructured Nanocrystals (HNCs) for High-Sensitivity and Humidity-Resistant...

All-inorganic cesium lead bromide (CsPbBr3) nanocrystals (NCs) demonstrate significant potential for unique room-temperature gas sensing of hazardous ammonia (NH3) via a dynamic vacancy passivation mechanism. The practical implementation of CsPbBr3-based NH3 sensors is significantly obstructed by challenges such as repeatability, humidity, and substantial response. We present the fabrication of Janus-type CsPbBr3-ZrO2 heterostructured nanocrystals (HNCs) as highly sensitive, humidity-resistant NH3 gas sensors operating at room temperature for the first time. A ZrO2 domain is selectively synthesized on a cubic CsPbBr3 NC in a Janus-type configuration, yielding two chemically distinct surfaces on a single particle. The exposed CsPbBr3 surface retains complete Br- vacancy accessibility for NH3 coordination, while the ZrO2 surface serves as a structural stabilizer and provides the composite with superior humidity resistance. A concept-based dual-mode NH3 gas sensor was developed based on a comprehensive experimental study and DFT calculations. Ultimately, with response and recovery durations of 17.46 and 25.31 s, respectively, at 100 ppm NH3, the enhanced Janus sensor attains a response ratio Ra/Rg of 8.4, particularly remarkable performance for a colloidal CsPbBr3 NC-based NH3 sensor. Moreover, after 70 h of operation at 60% relative humidity, the Janus sensor maintains 91% of its initial response, whereas unprotected CsPbBr3 NCs retain only 35%. The ZrO2 layer serves as a humidity resistance while permitting gas transmission, thereby markedly improving stability and functionality. This study characterizes the Janus approach for decoupling gas accessibility from humidity resistance in halide perovskite sensors and presents the inaugural use of Janus perovskite/oxide for NH3 gas detection.