Self-aligned CH3NH3PbBr3 perovskite nanowires via dielectrophoresis for gas sensing applications

https://doi.org/10.1016/j.apmt.2021.101307Get rights and content

Highlights

  • Morphological evolution of MAPbBr3 nanocubes to nanowires.

  • Self-alignment of single-crystalline MAPbBr3 nanowires.

  • MAPbBr3 channels exhibits the highest sensitivity for H2S gas molecules.

  • Adsorbed O2 molecules determine the MAPbBr3 response to the environmental species.

Abstract

Metal halide perovskites (MHPs) with environment-dependent optoelectronic properties can provide a new platform for highly sensitive and active gas sensor materials. While MHPs are a crystalline semiconductor with high carrier mobility and long carrier diffusion length, the formation of efficient channels for charge carriers can be hindered by the intrinsic point defects and impurities as well as grain boundaries in the solution-cast films with an uncontrolled morphology. Furthermore, a precise control of nanostructured MHP materials and their distribution with respect to device electrodes still remains challenging, which requires tedious efforts for additional fabrication. Herein, we demonstrate that the dielectrophoresis process can allow for self-alignment of single-crystalline MHP nanowires (NWs) with a uniform spatial distribution and orientation on interdigitated electrodes. We found that MAPbBr3 NWs array sensors exhibited the highest sensitivity (∼120% and τ = 40 s at 100 ppm) for H2S gas molecules among oxidizing (NO2) and reducing gases (NH2 and H2S), whereas no significant response was observed for MAPbCl3 NWs. The MAPbBr3 NW array-based sensor showed a long time stability exceeding one month with less than 20% derivation during first two weeks. The characteristic response of MHP NWs array significantly depends on the interaction of oxygen molecules adsorbed at their surface with the environmental target species, in which their surface conductivity can be modulated by the variation of trap states related to surface defects. Our work demonstrates a simple and facile route to synthesis and self-alignment of MHP NWs for chemiresistive gas sensors, broadening the range of technological applications of MHPs.

Graphical abstract

Single-crystalline MAPbBr3 and MAPbCl3 NWs with high surface area and characteristic surface moieties provide not only distinct optoelectronic properties but also strong and abundant analyte adsorption sites. Self-alignment of single-crystalline MAPbBr3 nanowires via dielectrophoresis provides a potential platform for chemiresistive gas sensors with high selectivity owing to their atmosphere-dependent electrical properties associated with the intermolecular interactions in the reversible adsorption and desorption process.

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Introduction

Metal halide perovskite (MHP) materials hold a promising potential for optoelectronic applications such as solar cells, light-emitting diodes, and photodetectors owing to a wide range of tunability in their energy band structures and the relevant light absorption and luminescence [1], [2], [3], [4], [5]. For the past few years, significant efforts have been devoted to understanding and improving their optoelectronic properties based on their diverse structural and chemical variability in a perovskite framework with a general formula of ABX3, where A+ cation is Cs+, MA+ (MA+ = CH3NH3+), and FA+ (FA+ = HC(NH2)2+), B2+ cation is mainly Pb2+, X halide is Cl, Br, and I [6], [7], [8], [9], [10], [11]. Moreover, low dimensional nanostructures such as nanocrystals (NCs) and nanoplatelets of MHPs have been adopted to achieve the physical properties (e.g. quantum confinement) unattainable using bulk MHPs due to the characteristic features in their morphologies [12], [13], [14], [15], [16], [17], [18]. However, uncontrolled formation of surface defects in MHP NCs has shown to introduce undesired trap states capturing mobile charge carriers, which have a great influence on the stability and performance of MHPs-based devices [19], [20], [21], [22], [23]. Therefore, a precise control of the surface charge recombination plays a crucial role in further optimization of MHPs-based devices relying on their electronic and optical properties.

While the surface passivation of MHP NCs has been widely performed using organic molecules containing amine-end groups, a few reports also showed that the environmental gas molecules can effectively interact with the ionic components such as metal cations and halogen vacancies at the MHP surface, resulting in a modulation of their photoluminescence (PL) and photostability as well as electrical resistance [24], [25], [26], [27]. For example, Loi and co-workers reported that the physisorption of oxygen and water molecules in MAPbBr3 single crystals can significantly enhance their PL intensity by over two orders of magnitude [24]. Bao et al. reported a resistive variation of MAPbI3 thin films when exposed to NH3 atmosphere [25]. These results indicate that the adsorption of environmental gas molecules can considerably affect the concentration of surface charge carriers and their transporting properties in the MHP materials. Furthermore, the MHP materials are a crystalline semiconductor with high carrier mobility and long carrier diffusion length, which give rise to efficient channels for charge carriers [28,29]. Thus, nanostructured MHPs with high surface area and versatile surface chemistry can provide a new platform for highly sensitive, active gas sensor materials.

Recently, Zhuang et al. demonstrated that polycrystalline MAPbI3-x(SCN)x film responds to acetone vapour and NO2 gases [30]. Xu and coworkers reported that gold-loaded MASnI3-SnO2 based gas sensor exhibited 240% of response for NO2 gas at 5 ppm with a recovery time of 12 s [31]. However, most of recent studies were focused on polycrystalline MAPbI3 and mixed halide MAPbI3-xClx thin films to detect O2, O3, or NH3 gas molecules although they are known to exhibit a permanent degradation against moisture and polar solvents accompanied by chemical decomposition and morphological changes [32], [33], [34]. Since this decomposition preferentially initiates at grain boundaries of MHP thin films, their electronic properties are significantly determined by their microstructure quality such as polycrystallinity, grain size, and defects, limiting the access to the intrinsic response of MHP materials to various environmental molecules [35,36]. Therefore, the fabrication of single-crystalline MHPs with enhanced stability and well-controlled nanostructure is important to understand how the environmental molecules interact with their surface moieties.

Herein, for the first time, we demonstrate alignment of single-crystalline MAPbCl3 and MAPbBr3 nanowires (NWs) via dielectrophoresis (DEP) on Au interdigitated electrodes (IDEs) as an ideal platform for chemiresistive gas sensors with high selectivity. The single-crystalline MHP NWs with a length of ∼25 μm could be grown in a liquid phase with excess organic ligands by kinetically controlled supersaturation of the precursor solution in the crystallization process. Under an electric field, DEP force exerted on the NWs allows a precise deposition of MHP NWs with respect to IDEs, resulting in a uniform and controlled alignment of NWs. The interaction mechanism of MHPs with the gas molecules could be understood by adsorption and desorption of oxygen molecules that manipulate the effective concentration of charge carriers along the MHP NWs. This concept is also supported by the presence of abundant O2 molecules at the surface of aligned MAPbBr3 NWs array that exhibited much higher selectivity in contrast to MAPbCl3 NWs array.

Section snippets

Materials

Lead(II) bromide (PbBr2, 99%), lead(II) chloride (PbCl2, 99%), methylammonium chloride (MACl, ≥ 98%), methylammonium bromide (MABr, ≥ 99%) n-octylamine (≥ 99%), and oleic acid (≥ 90%) were purchased from Sigma-Aldrich and used as received. Toluene (≥ 99%), N,N-dimethylformamide (DMF, ≥ 99.5%), and dimethyl sulfoxide (DMSO, ≥ 99.5%) were purchased from Daechung Chemicals & Metals and used as received.

Synthesis of MAPbCl3 nanowires

First, 10.72 mg (0.16 mmol) of MACl and 55.6 mg (0.2 mmol) of PbCl2 were dissolved in 2 mL of

Results and discussion

Single-crystalline MHP NWs were successfully synthesized by a modified reverse ligand-assisted reprecipitation (LARP) method, in which the preferential growth of crystals is attributed to the prolonged duration for the growth of the initially formed crystals under excess surface ligands (i.e. n-octylamine and oleic acid), as illustrated in Fig. 1a [37,38]. First, relatively uniform MHP cubes with an edge length of ∼2.5 μm were obtained by fast addition of toluene into the precursor solution. In

Conclusions

In conclusion, single-crystalline MAPbBr3 and MAPbCl3 NWs with high surface area and characteristic surface moieties provide not only distinct optoelectronic properties but also strong and abundant analyte adsorption sites. We demonstrated that the DEP process allows for a high level of control over the spatial distribution and orientation of single-crystalline MHP NWs that provide new opportunities as a new platform for highly sensitive, active gas sensor materials. MAPbBr3 NWs array sensors

CRediT authorship contribution statement

Artavazd Kirakosyan: Conceptualization, Methodology. Moon Ryul Sihn: Resources, Investigation, Data curation. Min-Gi Jeon: . Rezaul M.D. Kabir: . Jihoon Choi: Conceptualization, Writing – review & editing, Supervision, Funding acquisition.

Declaration of Competing Interest

The authors declare no competing financial interests.

Acknowledgements

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. NRF-2019R1I1A2A01060608, 2020R1I1A1A01062138).

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