Metal halide perovskite materials with the chemical formula ABX₃, where A is an organic or inorganic cation, B is a divalent metal and X is a halide anion have emerged as a leading class of semiconductors, offering exceptional structural and electronic properties for diverse applications. Furthermore, their reversible electrical or optical property changes in response to oxidizing or reducing environments make them prospective materials for gas detection technologies. The perovskite-based sensors operate efficiently at room temperature, offering an advantage over the traditional metal oxide gas sensors, eliminating additional energy consumption and enabling the development of portable gas sensing devices.^[1],[2] However, the presence of lead (Pb) in these materials poses a serious challenge for their widespread application and commercialization, owing to its toxicity. To address this issue, lead-free perovskite materials have recently gained increasing attention due to their environmental sustainability and potential for safer applications. The lead-free composition of these perovskites mitigates environmental and health risks associated with traditional lead-based materials and provides a sustainable platform for advanced sensing technologies. Their structural adaptability, coupled with room temperature operability, positions these materials as promising candidates for next generation medical diagnostics and environmental monitoring systems.

This study investigates lead-free Cs₂AgBiBr₆ perovskite synthesis and doping strategies to develop high-performance gas sensors for detecting volatile organic compounds (VOCs), as well as oxidizing and reducing gases. These sensors can be regarded as eco-friendly for the following reasons: they are lead-free; synthesized at room temperature without the use of hazardous organic solvents; function and recover efficiently at room temperature without the need for heating or UV irradiation; and operate under very low input voltage, significantly reducing overall energy consumption.

Lead-free Cs₂AgBiBr₆ perovskites were synthesized using precipitation method under ambient conditions and systematically doped with selected metals such as Zinc (Zn), Manganese (Mn), and Tin (Sn).  Due to doping, structural characterization through X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed significant improvements in crystallinity, grain size, and surface morphology. Energy dispersive spectroscopy (EDS) further validated the successful integration of dopants into the perovskite matrix. Additional analysis using UV-Vis spectroscopy provided critical insights into the material's optical properties, including light absorption characteristics and band gap energy, further showcasing the impact of doping on their performance.

The gas sensing capabilities of doped Cs₂AgBiBr₆ perovskites were assessed for VOCs such as Acetone and Limonene, which are established biomarkers for metabolic disorders, including diabetes and liver dysfunction. Moreover, detecting oxidizing and reducing gases in ambient air, such as Ozone (O₃) and Hydrogen (H₂), is crucial for environmental monitoring and safety applications. The sensors demonstrated sensitivity, selectivity, and rapid response times, even at low gas concentrations. Notably, all measurements were conducted at room temperature, eliminating the need for external heating and thereby reducing energy consumption while maintaining the integrity of the breath samples. This operational advantage makes the sensors both practical and efficient for real-world applications.

In summary, this work demonstrates the potential of lead-free, doped perovskites as sustainable and effective sensors for VOCs and inorganic gases, offering promising solutions for healthcare and environmental monitoring.