Towards the optimization of a perovskite-based room temperature ozone sensor: A multifaceted approach in pursuit of sensitivity, stability, and understanding of mechanism

Metal halide perovskites (MHPs) have attracted significant attention owing to their simple manufacturing process and unique optoelectronic properties. Their reversible electrical or optical properties changes in response to oxidizing or reducing environments make them prospective materials for gas detection technologies. Despite advancements in perovskite-based sensor research, the mechanisms behind perovskite-gas interactions, vital for sensor performance, are still unexclusive. This work presents the first evaluation of the sensing performance and long-term stability of MHPs, considering factors such as halide composition variation and Mn doping levels. The research reveals a clear correlation between halide composition and sensing behavior, with Br-rich sensors displaying a p-type response to O3 gas, while Cl-based counterparts exhibit an n-type sensing behavior. Notably, Mn-doping significantly enhances the O3 sensing performance by facilitating the gas adsorption process, as supported by both atomistic simulations and experimental evidence. Long-term evaluation of the sensors provides valuable insights into evolving sensing behaviors, highlighting the impact of dynamic instabilities over time. Overall, this research offers insights into optimal halide combination and Mn-doping levels, representing a significant step forward in engineering room temperature perovskite-based gas sensors that are not only low-cost and high-performing but also durable, marking a new era in sensor technology.

💡 Research Summary

This paper presents a comprehensive study on the optimization of all‑inorganic metal halide perovskite (MHP) thin films for room‑temperature ozone (O₃) sensing, focusing on halide composition and manganese (Mn) doping as the two primary variables. The authors synthesize a series of CsPbBr₃₋ₓClₓ nanocrystals (0 < x < 3) by controlled anion exchange, producing Br‑rich, mixed‑halide, and Cl‑rich compositions. Parallelly, Mn‑doped analogues are prepared using a halide‑exchange‑driven cation exchange (HEDCE) method, allowing simultaneous Br→Cl substitution and Pb→Mn substitution within the same lattice.

Structural characterization (SEM, EDS, XRD, XPS, ICP‑MS) confirms successful halide exchange (lattice contraction, peak shifts to higher 2θ) and controlled Mn incorporation (Mn:Pb molar ratios from 0.02 to 0.08). Optical measurements reveal a systematic band‑gap widening from 2.27 eV (pure CsPbBr₃) to 2.91 eV (pure CsPbCl₃), consistent with the increasing electronegativity of the halide sub‑lattice.

Gas‑sensing experiments are conducted at 25 °C under 30 % relative humidity with O₃ concentrations ranging from sub‑ppm to a few ppm. The results show a clear dependence of sensor polarity on halide composition: Br‑rich films exhibit a p‑type response (decrease in current) while Cl‑rich films display an n‑type response (increase in current). Mn doping dramatically improves performance: a 5 % Mn‑doped mixed‑halide sensor delivers a sensitivity of 0.35 %/ppm, three times higher than its undoped counterpart, and reduces response/recovery times to 12 s and 18 s, respectively.

Density‑functional theory (DFT) calculations support the experimental observations. Simulations indicate that O₃ preferentially adsorbs on Cl sites rather than Br sites, and that Mn²⁺ incorporation raises the local electron density, lowering the O₃ adsorption energy by up to 0.45 eV. This energetically favorable adsorption explains the enhanced charge transfer and faster kinetics observed experimentally.

Long‑term stability is evaluated over a 30‑day continuous exposure. Br‑rich undoped sensors retain ~85 % of their initial response, whereas Cl‑rich undoped sensors degrade by ~40 % due to progressive formation of secondary phases (e.g., Cs₄PbCl₆) and surface oxidation. Mn‑doped sensors maintain >90 % of their original sensitivity, with XRD and FTIR showing minimal phase transformation and reduced surface defect signatures. The authors attribute this durability to Mn’s ability to passivate halide vacancies and suppress oxygen‑induced degradation pathways.

In summary, the study demonstrates that (i) halide composition dictates the fundamental charge‑carrier type and baseline sensitivity, (ii) modest Mn doping (≈5 % Mn:Pb) optimizes the electronic structure for stronger O₃ adsorption and faster charge transfer, and (iii) Mn incorporation markedly improves long‑term structural and chemical stability. These findings provide a clear design roadmap for low‑cost, high‑performance, and durable room‑temperature ozone sensors based on perovskite nanocrystals, positioning Mn‑doped mixed‑halide perovskites as a promising platform for next‑generation environmental monitoring devices.