Materials Today
Volume 37, July–August 2020, Pages 56-63
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Piezo-phototronic effect enhanced polarization-sensitive photodetectors based on cation-mixed organic–inorganic perovskite nanowires

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Abstract

Piezo-phototronic effect has been extensively investigated for the third generation semiconductor nanowires. Here, we present a demonstration that piezo-phototronic effect can even be applied to tune polarization-sensitive photodetectors based on cation-mixed organic–inorganic perovskite nanowires. A big anisotropic photoluminescence (PL) with linearly polarized light-excitation was found due to a strong spontaneous piezoelectric polarization besides the anisotropic crystal structure and morphology. The piezo-phototronic effect was utilized to tune the PL intensity, and an improved anisotropic PL ratio from 9.36 to 10.21 for linearly polarized light-excitation was obtained thanks to the modulation by piezo-potential. And a circularly polarization-sensitive PL characterized with circular dichroism ratio was also discovered, which was found to be modulated from 0.085 to 0.555 (with a 5.5-fold improvement) within the range of applied strain. The circular dichroism was resulted from the joint effects of the modulated Rashba spin–orbit coupling and the asymmetric carriers separation and recombination for right- and left-handed helicity due to the presence of effective piezo-potential. These findings not only reveal the promising optoelectronic applications of piezo-phototronic effect in perovskite-based polarization-sensitive photodetectors, but also illuminate fundamental understandings of their polarization properties of perovskite nanowires.

Graphical abstract

In this work, we fabricated a cation-mixed organic–inorganic CsxMA1−xPbI3 perovskite nanowire, which revealed a better polarization sensitivity for not only linearly polarized light but also circularly polarized light. Interestingly, apart from the anisotropic crystal structure and morphology, it was demonstrated for the first time that the piezo-potential can also be used effectively to tune the linear-polarization sensitivity as well as circular-polarization sensitivity. These findings not only shed light on the promising optoelectronic applications of piezo-phototronic effect in perovskite-based polarization-sensitive photodetectors, but also reveal fundamental understandings of their polarization and spin-transport properties in perovskite nanowires.

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Introduction

In the field of traditional optical communication, the intensity, spectrum and spatial distribution of a light source are the three main parameters commonly used in our daily life. Polarization is another important information of light, hence the detection of polarization including polarization degree, polarization azimuth, ellipticity and circular polarization direction can greatly enrich the applications of light sensing [1], [2], [3]. Fabrication of anisotropic semiconductor structures, including anisotropic crystal structure and anisotropic morphology, is essential for the development of linear-polarization photodetectors [1], [4]. Semiconductor nanowires (NWs), with well-defined crystal and morphology anisotropy, have proven to be good candidates for linear polarization detection by means of light emission, absorption, and photoconductivity [1], [4], [5]. Semiconductor NWs especially with chip-level polarization sensitivity will have great potential in applications of future electronic circuits and optical chips. Over the past decade, halide perovskites have revealed excellent optical and optoelectronic properties, making them ideal candidates for the advancement of high-performance light sources, photodetectors and photovoltaic devices [6], [7], [8], [9], [10]. Recently, there are even reports on linear-polarization photodetectors based on organic–inorganic (CH3NH3)PbI3 (abbreviated as MAPbI3) and all-inorganic CsPbX3 (X = Cl, Br, I) lead halide perovskite nanowires [11], [12], [13]. There are also experimental evidences that lead halide perovskites possess a big spin–orbit coupling (SOC) which makes them outstanding performances in optoelectronic applications [14], [15], [16].

The three way coupling between piezoelectric effect, semiconductor and photoexcitation creates three main significant research fields, namely, piezophotonics, piezotronics, and piezo-phototronics [17], [18], [19]. Piezotronic and piezo-phototronic effects are extensively existed in third generation semiconductors, transition-metal dichalcogenides, and perovkites [17], [20], [21], [22], [23], [24]. Distinct from the first and the second generation semiconductors that are dominated by cubic crystal structure, such as Si, Ge and GaAs, the third generation semiconductors are dominated by non-cubic crystal structures such as Wurtzite and monoclinic etc, which lack of center symmetry. Therefore, piezoelectricity and piezotronic effect are the born characteristics of these semiconductors. The piezotronic effect involves utilizing the piezo-potential as a “gate” voltage to adjust/control the carrier transportation at the junction or interface. The piezo-phototronic effect is about the modulation of generation, separation, transportation or recombination of the photo-induced carriers at interfaces or junctions using the piezo-potential and piezoelectric charges. The piezo-phototronic effect has been used for many novel optoelectronic devices, for example, solar cells [25], [26], [27], LEDs [28], [29], photosensors [24], [30], spintronic devices [31], [32].

In this work, we fabricated a cation-mixed organic–inorganic CsxMA1−xPbI3 perovskite nanowire, which revealed a better polarization sensitivity for not only linearly polarized light but also circularly polarized light. What's more important, apart from the anisotropic crystal structure and morphology, it was demonstrated for the first time that the piezo-potential can also be used effectively to tune the linear-polarization sensitivity as well as circular-polarization sensitivity. This work indicates that the piezo-phototronic effect can also work at one semiconductor interior besides the interfaces and junctions. This experimental work also confirms the presence of a big SOC in this type of perovskite nanowires, which is derived from the inner piezo-potential. These findings not only shed light on the promising optoelectronic applications of piezo-phototronic effect in perovskite-based polarization-sensitive photodetectors, but also reveal fundamental understandings of their polarization and spin-transport properties in perovskite nanowires.

Section snippets

Results and discussion

Herein, we have successfully synthesized well-defined organic–inorganic CsxMA1−xPbI3 perovskite nanowires, where inorganic cation Cs+ is intentionally introduced to replace organic cation MA+ in order to induce a certain degree of inner strain which turns out to be good for bringing in a spontaneous piezoelectric polarization in the nanowires. Fig. 1a shows the growing processes of the nanowires via a two-step solution process on glass/ITO substrate with the size of 1 cm × 1 cm. The as-prepared

Conclusions

Linear and circular polarization-sensitive photodetectors based on cation-mixed organic–inorganic perovskite nanowires was fabricated. We found a big anisotropic PL with linearly polarized light-excitation, which was mainly derived from the strong spontaneous piezoelectric polarization in nanowires apart from the anisotropic crystal structure and morphology. Piezo-phototronic effect was utilized to tune the PL intensity, that is, the compressive strain was demonstrated to reduce the PL

Device fabrication

The glass/ITO was cleaned in turn by acetone, alcohol, and deionized water in ultrasonic cleaners for 15 min. To fabricate Csx(CH3NH3)1−xPbI3 nanowires, we firstly dropped 150 μL 24 mg/mL PbAc2·3H2O/H2O and DMSO (v:v = 2:1) solution and 50 μL PbI2 saturated aqueous solution to the ITO respectively to form a PbAc2·3H2O/PbI2 thin film and dried the thin film for 30 min at 65 °C to evaporate off the solvent. We then immersed the thin film formed on glass/ITO in 1 mL 40 mg/mL CH3NH3I and 1 mL

CRediT authorship contribution statement

Laipan Zhu: Conceptualization, Methodology, Data curation, Investigation, Writing - original draft, Writing - review & editing. Qingsong Lai: Methodology, Data curation, Investigation, Writing - original draft, Writing - review & editing. Wenchao Zhai: Visualization, Investigation. Baodong Chen: Visualization, Investigation. Zhong Lin Wang: Conceptualization, Formal analysis, Supervision, Writing - original draft, Writing - review & editing.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No. 11704032, 51432005, 5151101243, 51561145021), National Key R & D Project from Minister of Science and Technology (2016YFA0202704), Beijing Municipal Science & Technology Commission (Z171100000317001, Z171100002017017, Y3993113DF). We also thank professor Yong Ding at Georgia Institute of Technology for the helpful discussion of TEM.

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    These authors contributed equally to this work.

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