Cs2AgInCl6 Double Perovskite Single Crystals: Parity Forbidden

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Cs2AgInCl6 double perovskite single crystals: parity forbidden transitions and their application for sensitive and fast UV photodetectors Jiajun Luo, shunran Li, Haodi Wu, Ying Zhou, Yang Li, Jing Liu, Jinghui Li, Kanghua Li, Fei Yi, Guangda Niu, and Jiang Tang ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.7b00837 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on October 31, 2017

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ACS Photonics

Cs2AgInCl6 Double Perovskite Single Crystals: Parity Forbidden Transitions and Their Application For Sensitive and Fast UV Photodetectors Jiajun Luo,† Shunran Li,† Haodi Wu,† Ying Zhou,† Yang Li,† Jing Liu,† Jinghui Li,† Kanghua Li,† Fei Yi,‡ Guangda Niu,† Jiang Tang*†

†

Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic

Information, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan, Hubei 430074, China. AUTHOR INFORMATION ‡

School of Optical and Electronic Information, Huazhong University of Science and Technology

(HUST), Wuhan, 430074, China

Corresponding Author *E-mail: [email protected]

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ABSTRACT: Double perovskite Cs2AgInCl6 is newly reported as a stable and environmental friendly alternative to lead halide perovskites. However, the fundamental properties of this material remain unexplored. Here, we first produced high-quality Cs2AgInCl6 single crystals (SCs) with a low trap density of 8.6×108 cm-3, even lower than the value reported in the best lead halide perovskite SCs. Through systematical optical and electronic characterization, we experimentally verified the existence of the proposed parity-forbidden transition in Cs2AgInCl6 and identified the role of oxygen in controlling its optical properties. Furthermore, sensitive (dectivity of ~1012 Jones), fast (3dB bandwidth of 1035 Hz) and stable UV photodetectors were fabricated based on our Cs2AgInCl6 SCs, showcasing their advantages for optoelectronic applications.

TOC GRAPHICS

KEYWORDS: double perovskite, single crystals, parity forbidden transitions, surface treatment, UV detection


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Organic‒inorganic hybrid lead halide perovskites have emerged as one family of the most promising optoelectronic materials, due to their unique properties such as high absorption coefficients, long carrier diffusion lengths and low processing cost1-3. Various lead halide perovskite-based optoelectronic devices have been successfully achieved, including solar cells4, light emitting diodes5, lasers6, as well as photodetectors for ultraviolet, visible, and near infrared light detections7-11. Despite all these excellent properties, Pb-based hybrid halide perovskites suffer from two main issues, the high toxicity of lead12 and the intrinsic instability13. All these halide perovskites are highly soluble in water and could cause brain related symptoms when Pb poisoned. It is of great significance if Pb could be substituted yet their outstanding performance could be preserved. Currently, Sn2+ has been used to replace Pb2+ in perovskite14. However, the Sn2+ cations tend to undergo oxidation due to the high-energy-lying 5s orbitals, rendering the corresponding perovskite extremely unstable in ambient atmosphere. Over the past one year, double perovskites (A2B(I)B’(III)X6) have been proposed as stable and environmental friendly alternatives to lead halide perovskites, with one B(I) and one B’(III) to substitute two toxic Pb2+ 15-26. Cs2AgInCl6 is newly reported as a lead-free stable double perovskite (Figure 1a) semiconductor with a wide band gap of 3.2 eV at room temperature19-21. The absorption of Cs2AgInCl6 is mainly limited to wavelengths shorter than 400 nm, making it attractive for UV light detection. Unlike other indirect band gap double perovskite materials including Cs2B(I)BiX6 and Cs2B(I)SbX6 (B(I) = Ag, Cu, Na)15,16,21, Cs2AgInCl6 exhibits a direct band gap through both first-principles calculations and experimental observations such as an ultra-long carrier lifetime (6 µs)19,21, which makes it a promising competitor to Pb-based halide perovskites for photodetectors.


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Recently, Yan and co-workers theoretically demonstrated the large difference between experimentally measured optical bandgap of 3.2 eV and photoluminescence emission energy of 2.1 eV is caused by the parity-forbidden transitions, which are due to the centrosymmetry of double perovskite and the lowest conduction band derived from the unoccupied In 5s orbitals26. Given the new interesting physical and chemical phenomena of Cs2AgInCl6, the optical and electronic properties deserve further investigation. High-quality perovskite single crystals (SCs), which are free of the grain boundaries and noncrystalline domains, are commonly regarded as the ideal platform to study the fundamental properties as well as the surface properties. Furthermore, the low trap density (towards 108 cm-3) renders them more advantageous for applications in the field of solar cells and photodetectors. Especially for UV light detection, the trap states, despite introduce gain and enhance sensitivity, are often responsible for the sluggish response. Traditionally, oxides such as zinc oxide (ZnO) and tin oxide (SnO2), exhibit slow time response of well over one second due to the easy formation of massive oxygen vacancy27-31. In contrast, the expected low trap density, limited absorption to wavelengths shorter than 400nm, as well as ultra-long carrier lifetime, all make Cs2AgInCl6 SCs an ideal candidate for UV detections such as fire and missile flame detection and optical communications. In this article, we prepared high-quality Cs2AgInCl6 single crystals (SC), achieving an ultralow trap-density as low as (8.6±1.9) ×108 cm-3, even lower than the highest-quality Pb-based perovskites ((1.80±1.07)×109 cm-3)33. We experimentally verified the existence of parityforbidden transition in Cs2AgInCl6 and identified the role of oxygen in controlling its optical properties. Furthermore, fast (3dB cutoff frequency of 1035 Hz), sensitive (On-OFF ratio of


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~500, measured detectivity of ~1012 Jones), nontoxic and stable UV detectors were fabricated based on Cs2AgInCl6 SCs, which compared favourably to most UV detectors reported in the literature10,11,29-32.

Figure 1. Synthesis and optimization of Cs2AgInCl6 SCs. a) Structure of the ordered double perovskite Cs2AgInCl6. Yellow, pink, cyan and blue spheres represent In, Ag, Cs, and Cl atoms, respectively. b) and c) Current-voltage curves for the Cs2AgInCl6 SC grown from 0.067M and 0.05M precursor solution, respectively. Linear and quadratic fitting are applied according to the space charge-limited current (SCLC) model. Top inset in panel b: device structure for SCLC measurement where Cs2AgInCl6 SC was sandwiched by two Au electrodes deposited by thermal evaporation on opposite sides. Insets at the bottom of panel b and c: the photographs of corresponding SCs for SCLC measurements. d) Absolute transparency of single crystals synthesized with precursor concentration of 0.067M and 0.05M, respectively. e) XRD and


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Rietveld refined results of Cs2AgInCl6 powders. f) XRD of Cs2AgInCl6 SCs. The inset is the high-resolution XRD of (222) diffraction. Here, we introduced a hydrothermal method to grow high-quality Cs2AgInCl6 SCs in a confined space of Teflon autoclave (Figure S1a). The temperature was set to 180 °C to ensure the complete dissolution of precursors. Subsequently, the solution was slowly cooled at 0.5 °C per hour to promote crystal growth. The hydrophobic nature of the Teflon autoclave makes Cs2AgInCl6 nucleate in the solution rather than at the beaker wall, thus reducing the number of nuclei and assuring the crystal large enough for further characterization. As-prepared SCs possessed truncated octahedral shape with an average size of 2.88 mm×2.81 mm×1.95 mm and shiny surfaces (Figure 1b, c, inset). Interestingly, all the crystals show light yellow color on the surface but colorless interior, which will be explained later (Figure S1b, c). The crystal quality was optimized through tuning the precursor concentration (0.050 M and 0.067 M) due to ultralow solubility of the precursor materials in concentrated HCl (AgCl has a solubility limit of ~0.02 M at 298K). The trap density (ntrap) and carrier mobility (µ) was quantitatively studied through space charge limited currents (SCLC) method on the freshly prepared samples2. It should be noted that valid SCLC measurements require: i) at least one electrode should be ohmic; ii) the carrier mobility and dielectric constant should be independent on applied voltage; and iii) surface conducting path should be absent. At low bias voltages, we could clearly see a linear Ohmic region (red line). With increasing bias voltage, the current transited to a trap-filled limit (TFL) region (n > 3), and finally evolved into the square region (n = 2). The onset voltage VTFL (1.5 V for 0.067 M, 6.5 V for 0.050 M) was used to calculate the trap density. The single crystals derived from 0.067 M solution showed an extremely low trap density of (8.6±1.9)×108 cm-3, much lower than that from 0.050M solution ((7.3±1.7)×109 cm-3). It should be noted that the


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trap density of as-grown Cs2AgInCl6 was even lower than that in most of lead trihalide perovskite SCs29. Furthermore, from the quadratic Child region (n = 2), we can extract the carrier mobility of Cs2AgInCl6 SCs. For the crystals grown from 0.067 M and 0.05 M precursor solution, the mobility was calculated to be 3.31 cm2 V-1 s-1 and 2.29 cm2 V−1 s−1, respectively. The change of crystal quality could also be reflected by the crystal transparency (Figure 1d). The absolute transparency (2/1), calculated based on the reflection, scattering, and transmittance of Cs2AgInCl6 SCs, is expected high in a selected wavelength window for a clear crystal with less scattering and absorption (Figure S3). Here we measured the absolute transparency by a spectrophotometer with an integrating sphere, and the measuring method was described elsewhere29. Clearly, the ratio of 2/1 of SC from 0.067 M solution was ~75%, higher than that from 0.050 M solution (~60%), confirming the crystal quality. All these results show that growing Cs2AgInCl6 SCs in 0.067 M precursor solution yields better crystals with improved optical and electronic properties. X-ray diffraction (XRD) of the optimized SCs showed a strong diffraction peak of (222) plane, and three weak peaks of (111), (333) and (444) planes, revealing obviously that the single crystal was orientated along the (111) direction. The full width half maximum (FWHM) of (222) diffraction peak reached 0.05° (180 arcsec), indicating its high single crystallinity (Figure 1e, inset), which is further confirmed by single crystal X-ray diffraction analysis (Figure S4). As shown in Figure 1f, the experimental XRD values and the corresponding Rietveld refined results of Cs2AgInCl6 powder grinded from crystals showed a typical perovskite structure with lattice parameter of a=b=c=10.478 Å, consistent with literature report19,21. X-ray photoelectron spectroscopy (XPS) results exhibited the existence of the four elements in as-prepared SCs (Figure S6).


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Figure 2. The identification of the parity-forbidden transitions in Cs2AgInCl6 experimentally. a) Schematic illustration of the parity-forbidden transitions of Cs2AgInCl6. b) Absorption spectrum of Cs2AgInCl6 SCs. Weak absorption was observed around 595 nm. Inset: Tauc plot showing the characteristics of a direct band gap of 3.2eV (384 nm). c) Photoluminescence spectra (excited by 325 nm wavelength laser) of Cs2AgInCl6 crystal in the range of 350 nm to 800 nm. d) and e) Time-resolved room-temperature PL decay of Cs2AgInCl6 SCs monitored at 425 nm and 595 nm. We further measured absorption and photoluminescence (PL) of the optimized Cs2AgInCl6 SCs. Based on Yan’s calculation, there are parity-forbidden transitions from valence band maximum (VBM) to conduction band maximum (CBM) due to the same even parity of VBM and CBM, and the same goes for the CBM and VBM-1 located between VBM and VBM-226. However, transitions from a lower level VBM-2 to CBM are parity-allowed, which is ~1.10 eV larger than the fundamental bandgap between VBM and CBM (Figure 2a). As shown in Figure 2b, we


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indeed observed two absorption edges, with a sharp absorption starting at 384 nm (3.2 eV) while an extremely weak one near 595 nm (2.1 eV). The PL spectrum was obtained using a 325 nm excitation laser through a confocal Raman system (Ocean Optics USB 2000). When we focused the excitation beam on the SC surface, only one PL peak centered at 595 nm was observed. In contrast, when we intentionally focused a high power laser (~25 mJ cm-2) inside the SC, a strong peak at 595 nm and a relatively weak satellite peak at 425 nm appeared (Figure 2c). To confirm the two transition types, time-resolved room-temperature PL spectrum was conducted by monitoring 425 nm and 595 nm peaks. With an excitation laser wavelength of 365 nm, the PL decay curve at 425 nm composed of an initial fast component with a lifetime of 0.9 ns (64.3%), an intermediate component of 2.8 ns (31.8%), and a slow component of 9.8 ns (3.9%). Such short lifetimes are indicative of radiative recombination between electrons in CBM and holes in VBM-2; they also suggested that the photo-excited holes underwent a rapid nonradiative relaxation process from VBM-2 to VBM (Figure 2d). On the contrary, the PL lifetime of Cs2AgInCl6 SCs at 595nm was much longer (Figure 2e): a fast component of 65.3 ns (97.0%) and a slow component of 566.9 ns (3.0%). The relatively long lifetime was attributed to the parity-forbidden transitions from CBM to VBM, which was similar to emission in rare earth ions with PL lifetime in µs to ms scale35.


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Figure 3. Effects of oxygen in controlling optical properties on the surface of Cs2AgInCl6 SC. It should be noted that we firstly conducted UV-O3 treatment on pristine Cs2AgInCl6 SC, and after that we conducted vacuum treatment on UV-O3 treated sample. a) Absorption spectra of the same Cs2AgInCl6 SC (wavelength between 450 nm and 600 nm) before and after different treatments. b) Photoluminescence spectra (excited by 532 nm laser) of Cs2AgInCl6 SC before and after different treatments. c) XPS spectra of Cs2AgInCl6 SC for O 1s before and after etching. d) Bias dependent photoconductivity of the same Cs2AgInCl6 SC after different treatments. The different colors and emitting behaviors from the surface and interior of the crystals indicate their different compositions. If soaking the light yellow colored crystal into heated concentrated HCl solution for several hours, the crystal became totally colorless and transparent. In contrary, UV-O3 treatment could deepen the yellow color on surface. As shown in Figure 3a, after UV-O3 treatment, absorption from 450 nm to 600 nm significantly increased, showing the relaxation of


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parity-forbidden transitions from VBM to CBM. When the same sample was vacuumed further for 90 minutes, the absorption declined back to some degree. Similarly, 532 nm wavelength laser was used to excite the transitions from VBM to CBM , the PL peak at 595 nm also increased after UV-O3 treatment, and decreased back with further vacuum treatment (Figure 3b), consistent with the absorption results. Furthermore, the photoresponse towards 530 nm wavelength light was also tested on the same crystal, and the light-to-dark current ratio showed a significant increase after the UV-O3 treatment and decreased back with further vacuum treatment (Figure S7). The above phenomenon suggest oxygen or oxygen-containing functional groups altered the surface composition and thus optical properties, which was commonly found in hybrid perovskite34,36,37 and traditional oxides27. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical composition of Cs2AgInCl6 SCs surface. As shown in Figure 3c, the surface of Cs2AgInCl6 SCs showed a strong oxygen 1s peaks compared to the Ar-ions etched sample, indicating high-vacuum environment in XPS measurements could not remove the chemically attached oxygen species completely. The oxygen was from hydroxyl group and oxygen anions considering the fitted binding energy at 531.5 eV and 533.0 eV, respectively. Moreover, after UV-O3 treatment, Ag 3d and In 3d peaks shifted to lower binding energy (Figure S8), also indicating the formation of Ag-O/Ag-OH and In-O/In-OH species38-39. Theoretically, oxygen (O) substitution of chlorine (Cl) either in bulk or on surface could break the local structure of double perovskites and create defect states in the bandgap, which influences the optical properties of Cs2AgInCl6. Besides optical properties, the electronic properties of SCs surface were also crucial for high quality SCs34, 36. To evaluate the influence of adsorbed oxygen on electronic properties, surface


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recombination velocity s was measured by the photoconductivity method. The measured photocurrent was fitted to a modified Hecht equation34, 40:

I

(1)

Where L is the thickness, I0 is the saturated photocurrent, is the carrier lifetime and V is the applied bias. The device structure was the same as SCLC characterization and the illumination light used here was 365 nm LED. The bias dependent photoconductivity of pristine, UV-O3 treated, vacuum treated Cs2AgInCl6 SC are shown in Figure 3d. The surface recombination velocity s of pristine Cs2AgInCl6 was calculated to be 1002 cm s–1, and the UV-O3 treated and vacuum treated Cs2AgInCl6 SC have a s value of 1758 and 1580 cm s-1, respectively, indicating that the oxygen species attached on the SCs surface introduce surface recombination centers.

Figure 4. Photoelectric performance of our photoconductive detector based on Cs2AgInCl6 SC in air and vacuum. a) The current–voltage characteristic of the detector in dark condition. Inset: the


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device configuration for photoconductive planar detector. b) Light-to-dark current-voltage (I−V) curves under 365 nm monochromatic illumination generated by a LED. The light power density is 2.36 mW/cm-2. c) Normalized response of the detector versus the input signal frequency (light intensity of 1.27 mW cm-2) at a bias voltage of 5 V. The -3dB point is marked with the dash line. d) Wavelength-dependent responsivity under 5 V bias. The light source is the bromine tungsten lamp modulated by optical grating to generate monochromatic light with a minimum step of 10 nm. e) Measured dark current noise at various frequencies under the bias of 5V for device in vacuum. The instrument noise floor, calculated shot noise and thermal noise limit are also included for reference. f) Light intensity-dependent responsivity and normalized detectivity under the bias of 5 V in vacuum. Finally, Cs2AgInCl6 SC-based visible-blind UV detectors with a photoconductive planar structure were fabricated. Two Au electrodes with interval of 200 µm are deposited by thermal evaporation onto the same side of crystal (Figure 4a, inset). Please note our current Cs2AgInCl6 SCs and resultant devices are self-standing. They could, in principle, be integrated with various substrates providing these substrates are acid solution resistive. To evaluate the effect of oxygen on device performance, we conducted all the measurements on the same device in air and vacuum, respectively. As shown in Figure 4a, the current–voltage curves in dark exhibited features expected from good Ohmic contacts. The resistivity of Cs2AgInCl6 in vacuum was calculated to be 2×1010 Ω, and decreased to 1.5×109 Ω under air exposure, and such conductivity change was attributed to the oxygen induced surface conductance. Under vacuum condition, the dark current under 5V bias reached 10 pA, resulting from the low carrier concentration, wide band gap, and low recombination rates. Such ultralow dark current guarantees detection of weak optical signals and high detectivity. Figure 4b showed the dynamic current-time (I–t)


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photoresponse under the repetitive switching of 365 nm monochromatic illumination at a bias of 5 V both in air and vacuum. The Ilight and Idark were stable as the reversible and rapid switch from illumination to dark. The photocurrent increased from 5 nA in vacuum to 8 nA in air, and such increase was from the defects induced gain of photocurrent. The −3dB cutoff frequency was applied to evaluate the response time of the devices, and the obtained −3dB point in air and vacuum were 473 Hz (2.11 ms) and 1035 Hz (0.97 ms), respectively (Figure 4c). In addition, when the vacuum device exposed to a rapid repetitive switching of 365 nm light, we extracted a rise and decay time as 0.8 ms and 1.0 ms, respectively (Figure S9), consistent with the -3dB cutoff frequency measurement. Such fast response time in vacuum was comparable to previously reported optimal MAPbCl3-based UV detectors (~1 ms)11 and much faster than the traditional oxides-based devices (~1s)27-30. Wavelength-dependent responsivity of our devices were shown in Figure 4d. The responsivity (R) can be calculated as: − /(! ∙ #)

(2)

Where Ip is the photocurrent, Id is the dark current, A is the active area of the device and P is the incident light power density. The device demonstrated negligible photoresponse in the wavelength range of 400 to 550 nm wavelength and then presented a steep rising edge located at ~390 nm. Under vacuum, we could completely suppress the response in the range of 410 to 550 nm, which was from the weak parity forbidden transition. The calculated responsivity toward 365 nm UV light is ~0.013 A/W at light power density of 10.5 µW/cm2.


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Based on the optimal performance in vacuum, the normalized detectivity, used for evaluating the ability to detect weak light of various photodetectors, was calculated by the following equation:

D* = ( Af )1/2 R / in

(3)

Where A is the effective area of the detector, f is the electrical bandwidth and in is the noise current. The noise current, which was associated with the dark current, bandwidth, temperature and various other noise sources, such as shot noise and thermal noise, cannot be derived simply from the dark current of the devices. Here we directly obtained the noise current by a spectrum analyzer. As shown in Figure 4e, the measured noise current of the Cs2AgInCl6 single crystal is approximately 1.55×10-15 A/Hz1/2, barely sensitive to frequency, indicating a negligible 1/f noise of our devices due to the low trap density and minimized grain boundaries of our Cs2AgInCl6 SCs. Another two common noise source, shot noise (in,s) and thermal noise (in,T), were calculated to be 1.27×10-15 A Hz-1/2 and 1.29×10-16 A Hz-1/2, respectively. %&,( )2+% , %&,- .

/01 -2 3

(4)

(5)

Where % is the dark current, + is the elementary charge, , is the electrical bandwidth, 45 is the Boltzmann constant, is the temperature and is the resistance of the device. Clearly, large resistivity resulted in low dark current and small shot noise. The total noise (%&,6 ) can be calculated by the equation below: %&,6 .%&,( 7 + %&,- 7

(6)


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in,t, including contributions from both shot noise and thermal noise, was calculated as 1.40×10-15 A Hz-1/2, close to the measured noise. At last, the calculated D* of our device was 9.60 × 10 Jones (Figure 4f). Besides, our device performance is compared with a few representative results of UV photodetectors adapted from literatures, as compiled in Table 1. Sensitivity and response speed are the two key parameters for photodetectors, and the product of detectivity and 3dB bandwidth is often used to compare the performance among different photodectors. Since in most literature papers only response times were reported, we hence use the detectivity-toresponse-time-ratio to evaluate the performance of photodetectors. Traditional oxides, such as ZnO, SnO2 and TiO2, suffer from slow response time. Obviously, our photodector exhibited the highest calculated detectivity-to-response-time-ratio among all these devices, showcasing the advantage of using Cs2AgInCl6 SC for UV detection. Table 1. Comparison of device performance of our Cs2AgInCl6 UV photodetectors with literature reported photodetectors.

Photodetectors

Dark current /nA

Dectivity /Jones

Response time /ms

Dectivity/ Response time

ZnO

~0.2

1.3*1013

>2.0*104

6.5*108

[29]

SnO2

5

/

[30]

/

[31]

~10

4

/

>5.0*10

3

Reference

TiO2

1.9

/

6.0*10

GaN

~0.01

9.3*1011

/

/

[32]

MAPbCl3 film

~1

~1012, estimated

~1.0

~1012

[11]

MAPbCl3 SC

415

1.2*1010

62

1.9*108

[10]

Cs2AgInCl6 SC

0.01

~1012

0.97

~1012

This work


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Figure 5. The stability studies. a) Thermogravimetric differential thermal analysis of Cs2AgInCl6 powder. b) PXRD patterns of Cs2AgInCl6 powder after exposure to humidity (55% RH). c) PXRD patterns of Cs2AgInCl6 powder after exposure to light (5.02 mW/cm-2). d) Device storage stability of Cs2AgInCl6 devices. Aging condition: ∼25 °C, ∼55% humidity, devices without encapsulation. The chemical and thermal stability of perovskite is another important criteria to assess their potential for practical applications. Thermogravimetric analysis (TGA) showed that Cs2AgInCl6 was stable until 507 °C (Figure 5a), much higher than organic-inorganic hybrid perovskites41, and no phase transition was observed before decomposition referring to the differential thermal analysis (DTA). The stability against moisture and light was investigated by storing either in the dark at 55% relative humidity for 5 months or irradiated at 50 °C with 365 nm and 530 nm LED at an intensity of 5.02 mW/cm-2 for 48 hours. As shown in Figure 5b, c, no decomposition was found according to the PXRD patterns. Furthermore, we investigated the durability of the


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Cs2AgInCl6 device, without encapsulation, by recording the photocurrent every 5 days. The device performance maintained 90% of the initial value after storage in ambient (∼25 °C, 55% relative humidity) for 60 days, demonstrating excellent device stability (Figure 5d). The oxygen contamination may influence the stability of devices, however, such degradation could be largely remedied by storing the devices in vacuum to eliminate surface contaminants. In summary, high-quality Cs2AgInCl6 SCs with a low trap-state density ((8.6±1.9) × 108 cm-3) were successfully grown by one-pot hydrothermal method. The existence of parity-forbidden transition in Cs2AgInCl6 was experimentally verified, and oxygen was found effective in controlling its optical properties. By eliminating oxygen contamination on the SCs surface in vacuum, we fabricated a Cs2AgInCl6 SC based visible-blind UV detector, with high ON-OFF ratio (~500), fast photoresponse (~1ms), low dark current (~10 pA at 5V bias) and high detectivity (~1012 Jones). Overall, our studies showed that Cs2AgInCl6 double perovskite SCs are promising for UV photodetection because of their nontoxicity, outstanding sensitivity, response time, as well as excellent stability. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: Experimental methods. Details of all the characterization techniques. Photographs, and additional data figures and analysis (PDF) AUTHOR INFORMATION Corresponding Authors


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*E-mail: [email protected]. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT J. Luo and S. Li contributed equally to this work. This work was financially supported by the Major

State

Basic

Research

Development

Program

of

China

(2016YFB0700700,

2016YFA0204000), the National Natural Science Foundation of China (91433105), and the HUST Key Innovation Team for Interdisciplinary Promotion (2016JCTD111). The authors also thank the Analytical and Testing Center of HUST and the facility support of the Center for Nanoscale Characterization and Devices, WNLO. In addition, the authors thank Dr. Zewen Xiao for useful discussions, and the authors also thank Prof. Xing Lu for single crystal X-ray diffraction analysis. REFERENCES (1).

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Cs2AgInCl6 Double Perovskite Single Crystals: Parity Forbidden

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