Passivated Single-Crystalline CH3NH3PbI3 Nanowire Photodetector

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Passivated Single-crystalline CH3NH3PbI3 Nanowire Photodetector with High Detectivity and Polarization Sensitivity Liang Gao, Kai Zeng, Jingshu Guo, Cong Ge, Jing Du, Yang Zhao, Chao Chen, Hui Deng, Yisu He, Haisheng Song, Guangda Niu, and Jiang Tang Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.6b03119 • Publication Date (Web): 01 Nov 2016 Downloaded from http://pubs.acs.org on November 2, 2016

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Passivated CH3NH3PbI3 nanowire polarization detector Abstract 29x10mm (300 x 300 DPI)

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Passivated Single-crystalline CH3NH3PbI3 Nanowire Photodetector with High Detectivity and Polarization Sensitivity Liang Gao‡, Kai Zeng‡, Jingshu Guo, Cong Ge, Jing Du, Yang Zhao, Chao Chen, Hui Deng, Yisu He, Haisheng Song, Guangda Niu, Jiang Tang* Wuhan National Laboratory for Optoelectronics (WNLO) and School of Optical and Electronic Information, Huazhong University of Science and Technology (HUST), Wuhan, 430074, China

KEYWORDS: single-crystalline CH3NH3PbI3 nanowire, passivation, high detectivity, polarization sensitivity

ABSTRACT: Photodetectors convert light signals into current or voltage outputs and are widely used for imaging, sensing and spectroscopy. Recently, perovskite-based photodetectors have shown high sensitivity and fast response due to the unprecedented low recombination loss in this solution processed semiconductor. Among various types of CH3NH3PbI3 morphology (film, single crystal, nanowire), single-crystalline CH3NH3PbI3 nanowires are of particularly interesting for photodetection because of their reduced grain boundary, morphological anisotropy and


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excellent mechanical flexibility. The concomitant disadvantage associated with the CH3NH3PbI3 nanowire photodetectors is their large surface area, which catalyzes carrier recombination and material decomposition, thus significantly degrading device performance and stability. Here we solved this key problem by introducing oleic acid soaking to passivate surface defects of CH3NH3PbI3 nanowires, leading to device with much improved stability and unprecedented sensitivity (measured detectivity of 2×1013 Jones). By taking advantage of their one-dimensional geometry, we also showcased, for the first time, the linear dichroic photodetection of our CH3NH3PbI3 nanowire photodetector.

Methylammonium lead triiodide perovskite (CH3NH3PbI3) has emerged as a star material for optoelectronic devices due to its suitable bandgap, large optical absorption coefficient, long electron-hole diffusion length, benign defect physics and low-cost solution processing.1-4 Solar cells employing CH3NH3PbI3 as the absorber have obtained a certified 22.1% efficiency, and photodetectors, either photodiodes or photoconductors, have demonstrated fast and sensitive light sensing. Using single-crystalline CH3NH3PbI3 nanowires for photodetection possesses several advantages over their thin film counterparts due to the following reasons: i) Reduced grain boundary exists in these single-crystalline perovskite nanowires, thus permitting a much smoother charge flow within the single-crystalline channel and enabling better device performance5-7; ii) The one-dimensional structure introduces morphological anisotropy which could be utilized to detect polarized light despite the highly isotropic crystal structure of CH3NH3PbI3; iii) The excellent mechanical property of CH3NH3PbI3 nanowires brings opportunity for construction of highly flexible photodetectors on polymer substrates; iv) Such


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one-dimension nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of structure properties for various applications8,9. In addition, some reports also indicate that singlecrystalline perovskite nanowires have very low defect levels and impressive photophysical properties comparable or even better than their large single crystal counterpart10-13, further highlighting the potential of perovskite nanowires for photodetection.

The concomitant disadvantage associated with optoelectronic devices employing nanowires is their large surface area to volume ratio. CH3NH3PbI3, despite its outstanding bulk defect physics due to its perovskite symmetry, large lattice constant and strong antibonding between Pb s orbital and I p orbitals14, still suffers from highly disordered structure on the surface that creates electronic trap states15. Moreover, the large surface area also acts as culprit that catalyzes CH3NH3PbI3 decomposition when subject to moisture and light exposure, thus degrading device stability. So far, there are many reported methods to synthesize CH3NH3PbI3 nanowires, such as spin-coating16,17, film etching18, template guided growth19,20, micro-gravure printing21, one-step self-assembly22, and so on. However, investigations of nanowire passivation are rather limited, if not any, compared to perovskite thin film23-27. Consequently, many of these CH3NH3PbI3 nanowire based photodetectors showed unsatisfactory device performance and stability6,7,22. Based on their success in perovskite solar cells, we believe that carefully engineered passivation of CH3NH3PbI3 nanowires could remedy defect states on the surface and simultaneously improve device stability, thus pushing CH3NH3PbI3 nanowire photodetectors to an even more competitive level.


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In this work, we continued and further optimized our one-step self-assembly method to synthesize CH3NH3PbI3 nanowires array6. Three strategies were implemented to passivate CH3NH3PbI3 nanowires and oleic acid (OA) soaking turned out to be the best one. This treatment doubled the photocurrent, reduced by half the dark current, and remarkably improved device stability, leading to CH3NH3PbI3 nanowire photodetectors (CNPD) with much improved device performance. Photoluminescence (PL) and space-charge-limited-current (SCLC) measurements revealed that OA soaking treatment substantially reduced trap density, extended carrier lifetime and increased carrier mobility. As a result, our OA-passivated CNPD demonstrated submillisecond response time, 4.95 A W-1 responsivity, and measured detectivity of 2 × 1013 Jones, which is the highest measured detectivity reported so far for any photodetectors based on CH3NH3PbI3. This value is five times better than commercial Si-based photodetectors (4 × 1012 Jones). Furthermore, by taking advantage of the anisotropic geometry of CH3NH3PbI3 nanowires, we realized, for the first time, strong polarization dependent light detection of CNPD, which further expands the potential application of organic-inorganic hybrid perovskite photodetectors.


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Figure 1. Characterization of CH3NH3PbI3 nanowires. (a) Top-view SEM image of CH3NH3PbI3 nanowire array. (b) AFM image of a single CH3NH3PbI3 nanowire. The inset is the crosssectional SEM image of one CH3NH3PbI3 nanowire. (c) HRTEM image of CH3NH3PbI3 nanowire. The inset shows the typical low-resolution TEM image. (d) High-quality SAED pattern of CH3NH3PbI3 nanowire. (e) XRD pattern and (f) Absorption and PL spectra of CH3NH3PbI3 nanowire array.

For the nanowire growth, 3 µL 1wt% CH3NH3PbI3 dimethylformamide (DMF) precursor solution was dropped onto a ~10° slope glass substrate (size 1.5 × 1.5 cm). Along with drying out of DMF, an array of CH3NH3PbI3 nanowires took shape from top to bottom. To improve the nanowire crystallinity, the product was heated at 70 oC for 10 minutes in ambient. During the heating process, DMF volatilized and fast CH3NH3PbI3 nanowires growth (estimated as ~0.2


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mm/min) occurred at the edge of the droplet recession, probably from the first precipitation of less soluble PbI2 and then reacting with CH3NH3I to generate CH3NH3PbI3 nanowires. A movie recording the growth process by optical scope is shown in the supporting information, along with the snapshots shown in Figure S1. The width of these CH3NH3PbI3 nanowires varies from 100 nm to 2 µm, while their length could be up to 2 mm, corresponding to an aspect ratio of more than one thousand (Figure 1(a)). A cross-sectional scanning electron microscopy (SEM) image, shown as the inset in Figure 1(b), reveals that the cross-section geometry of CH3NH3PbI3 nanowires is approximatively rectangular, reminiscent of its tetragonal crystal structure. The atomic force microscopy (AFM) image in Figure 1(b) also indicates the width of CH3NH3PbI3 nanowire is 2-3 times of its height. High resolution transmission electron microscopy (HRTEM) image of CH3NH3PbI3 nanowire (Figure 1(c)) reveals clear lattice fringes with a lattice spacing of 0.31 nm, which could be indexed as (004) or (220) of the tetragonal CH3NH3PbI3 phase28. The ultra-clear HRTEM image and the corresponding high-quality selected area electron diffraction (SAED) pattern (Figure 1(d)) indicate the single-crystalline nature of our CH3NH3PbI3 nanowires. This is supported by the fact that HRTEM and SAED measurements on different spots of one CH3NH3PbI3 nanowire and/or on different CH3NH3PbI3 nanowires demonstrate similar results. X-ray diffraction (XRD) pattern in Figure 1(e) further indicates high crystalline quality of CH3NH3PbI3 nanowires and their preferential growth along [110] direction according to the strongest (110) and (220) diffraction peaks, similar to the results reported by others6,7. Figure 1(f) displays the UV-Vis absorption and photoluminescence (PL) spectra of CH3NH3PbI3 nanowires. The absorption edge is at ~800 nm, and the PL peak is at ~780 nm with the full width at half maximum (FWHM) of about 50 nm. All these characterizations combined confirmed that


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high-quality single-crystalline CH3NH3PbI3 nanowires with [110] preferred orientation were obtained through our simple one-step self-assembly strategy.

Figure 2. The structure of CNPD and different passivation influences on the performance of CNPD. (a) Schematic of device structure of our CNPD. (b) Light-dark current-voltage (I-V) curves of the CNPD under 530 nm monochromatic illumination generated by a LED. The light power density is 2.36 mW cm-2. (c), (d) and (e) Transient photoresponses of CNPDs with different post-treatments to compare which passivation is the best. The post-treatments are oxygen plasma exposure (OP), CH3NH3I IPA soaking (MAI) and oleic acid toluene soaking (OA), respectively. Testing condition: 530 nm monochromatic illumination, 2.36 mW cm-2, 10 s per cycle. (f) Comparison of device storage stability of four CNPDs with different passivation. Aging condition: ~20 ℃, ~50% humidity, devices without encapsulation.

In order to explore the photoelectric performance of CH3NH3PbI3 nanowires, gold electrodes with a gap of 200 µm and a width of 1.5 cm were deposited by thermal evaporation. The device


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structure of our CNPD is schematically shown in Figure 2(a). Under a 2.36 mW cm-2 monochromatic 530 nm light illumination, our device demonstrates a light-to-dark current ratio of 250, as evidenced in Figure 2(b). Notably, under 1 V bias, the dark current is only dozens of pA, which is much lower than the perovskite film and single crystal photoconductive detector29,30. As mentioned above, the 1D-configuration nanowires have disordered zone on their surface, acting as defects to annihilate photo-excited carriers through recombination loss. Our CH3NH3PbI3 nanowires are grown in an ultrafast manner (0.2 mm/min) that could generate more defects on the surface and hence urgently need effective passivation15,31,32 to reduce these detrimental surface defects. According to the passivation effect of oxygen to perovskite film15,33, the retardant effect of MAI to CH3NH3PbI3 decomposition6 and the protection effect of OA to perovskite QDs34, three kinds of selected strategies for passivation of CH3NH3PbI3 nanowires were explored, which are oxygen plasma exposure (OP), CH3NH3I isopropanol soaking (MAI) and oleic acid toluene soaking (OA), respectively. After passivation, the corresponding dynamic current-time (I-t) photoresponse of these devices are displayed in Figure 2(c)-2(e). Clearly, oxygen plasma treatment reduces the dark current at the price of sacrificed photocurrent, and CH3NH3I soaking increases dark current and photocurrent simultaneously. Only the OA passivation demonstrates the best gain in terms of device performance. It not only reduces the dark current, but also increases the photocurrent, similar to our previous study of Ag nanoparticles doping in PbS quantum dot matrix35. Statistics of more than 100 samples revealed that this is not an artefact or device dependent observation but general for our CNPDs; all these devices demonstrated a few times increase in the light-to-dark current ratios after oleic acid passivation. Furthermore, OA passivation also greatly improves the ambient storage stability of our unencapsulated devices, as shown in Figure 2(f), because of its hydrophobic encapsulation


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by the 2 nm long oleate ligand. After one-month storage in air, the photocurrent fades to 94% for the OA passivated device, 71% for the oxygen plasma treated device, 49% for the CH3NH3I soaked device and 28% for the untreated control.

Figure 3. Understanding the beneficial effect of OA passivation on CH3NH3PbI3 nanowires. (a) Photoluminescence intensity and (b) decay transient comparison between control and OA treated CH3NH3PbI3 nanowires at the same test conditions. The excitation power is 50 mW and the monitored wavelength is 780 nm. Photoluminescence decay was monitored at the wavelength of 780 nm. Space charge limited current measurement on (c) control and (d) OA treated CH3NH3PbI3 nanowires. The red and green lines are the linear and quadratic fitting of the I-V plots, respectively.


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We sought to photoluminescence and space charge limited current (SCLC) characterizations to understand the positive effect of OA treatment on CH3NH3PbI3 nanowires. Photoluminescence measurements were tested at the same point on the nanowire before and after OA passivation following identical conditions to ensure credible comparison. As shown in Figure 3(a), photoluminescence intensity significantly enhances upon the OA treatment, indicating that OA passivation increases the radiative recombination of photo-excited carriers and reduces the surface trap density of CH3NH3PbI3 nanowire. Figure 3(b) displays transient photoluminescence decay traces of CH3NH3PbI3 nanowire arrays under exactly identical testing conditions. These decays could be well fitted with bi-exponential decays. The fast decay component is attributed to bimolecular recombination36, and the slow decay component comes from radiative recombination of free carriers from which carrier lifetime is obtained37. After OA passivation, carrier lifetime increases from 28.1 ns to 51.3 ns, indicating OA treatment reduces non-radiative recombination centers at nanowire surface and renders more time to collect and transport photogenerated carriers in the photodetectors.

Table 1. Physical properties of CH3NH3PbI3 nanowires before and after OA passivation. Samples

Mobility

Carrier density

Carrier lifetime

(cm2V-1s-1)

(cm-3)

(ns)

Control

2.47

1.22E12

28.1

OA Passivated

4.41

1.16E11

51.1


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Figure 3(c) and 3(d) show the SCLC evolutions of CNPD with OA passivation under bias from 0.08 to 100 V. Both linear and quadratic region in the current-voltage curves are observed, justifying the SCLC analysis. By analyzing the square-law region, the injected dark current density can be derived by the Mott-Gurney law: 9 V2 J D = ε 0εµ 3 8 L

(1)

where εo and ε are absolute and relative dielectric constant, µ is mobility, V is the bias voltage and L is the channel width, respectively. Using the parameter given in supplementary information, the mobility can be worked out through equation 1. By analyzing the linear region, the JD ~ V characteristics obey the Ohm law as

J D = σ E = epµ

V L

(2)

where σ is conductivity and p is the carrier density, respectively. By substituting µ into equation 2, the carrier density can be calculated. As summarized in Table 1, the mobility of OApassivated nanowires increases about two times, from 2.47 cm2/Vs to 4.41 cm2/Vs, and the carrier density reduces about ten times, from 1.22 × 1012 cm-3 to 1.16 × 1011 cm-3. Hence, the decreased product of mobility and carrier density makes the dark current of OA-passivated CNPD lower, and the enhanced mobility and carrier lifetime boost the photocurrent. The trapfilled limit voltage decreases from 10 V to 2.5 V through OA passivation, indicating the trap density of CH3NH3PbI3 nanowires reduces to a quarter. To an atomic level, we believe that OA can passivate exposed Pb ions on the surface of CH3NH3PbI3 nanowire through a deprotonation process, forming lead-oleate bond (Pb-OOC-R) as evidenced by FTIR spectra in Figure S3, in analogy to their passivation of PbS quantum dots38 and perovskite quantum dots34,39. Such a


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hydrophobic oleate sheath (~2 nm thick) also encapsulates the CH3NH3PbI3 nanowire, preventing the moisture erosion and decomposition of CH3NH3PbI3 crystal.

Figure 4. Photoelectric performance of OA-passivated CNPD. (a) Wavelength dependent photocurrent and responsivity. The bias is 1 V. The light source is the bromine tungsten lamp modulated by optical grating to generate monochromatic light with a minimum step of 10 nm, as shown in Figure S4. (b) The transient response (current-time curve) of our CNPD. Each cycle is 30 ms and the sampling interval is 0.1 ms. (c) Measured current noise at various frequencies. The blue dash line displays the reported values of perovskite film based photodetector40. The red dash line is the shot noise limit. (d) Light intensity dependent responsivity and detectivity. The bias is 1 V. The light intensity varies over 6 orders of magnitude and the emitting wavelength is 530 nm.


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Table 2. Device performance comparison between OA-passivated CNPD and similar photodetectors employing CH3NH3PbI3 film, microwires or nanowires reported in the literatures. Ref.

Materials

Configuration

Responsivity (A/W)

Detectivity (Jones)

Response time

41

CH3NH3PbI3 Film

PD

242@-1 V

Not Given

41 us

40

CH3NH3PbI3 Film

PD

Not given

8*1013 (C)

140 ns

29

CH3NH3PbI3 Film

PC

3.49@3 V

Not Given

< 0.1 s

18

CH3NH3PbI3 NW

PC

Not Given

Not Given

0.12 s

16

CH3NH3PbI3 NW

PC

5*10-3@1V

Not Given

0.25 ms

6

CH3NH3PbI3 NW Network

PC

0.10@10 V

1.02*1012 (C)

0.3 ms

22

CH3NH3PbI3 NW

PC

0.85@1 V

2.5*1012 (C)

0.2 ms

7

CH3NH3PbI3 MW

PC

13.57@-5V

5.25*1012 (M)

80 us

Ours

CH3NH3PbI3 NW

PC

4.95@1 V

2*1013 (M)

1014 Jones for 530 nm light detection. However, this value is heavily overestimated because the measured noise in the dark presented a strong 1/f component (supplementary Figure S6), which was neglected in the estimation. We thus measured the noise spectrum in Figure 4(c) and took in=5.48 × 10-14


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A/Hz1/2 at 1 Hz to calculate the detectivity as 2 × 1013 Jones. Our device performance is compared with a few representative results of CH3NH3PbI3 photodetectors adapted from literatures, as compiled in Table 2. Obviously, our OA-passivated CNPD exhibits the highest measured detectivity among all these devices, fully showcasing the effectiveness of using OA passivation to improve device performance.

Figure 5. Linear dichroic photodetection of our OA-treated CNPD. (a) Simulation diagram of perovskite nanowire under polarized light simulated in finite difference time domain (FDTD). (b) Calculated absorption ratio of CH3NH3PbI3 nanowire when light polarization direction is in parallel with (θ=0°) or perpendicular to (θ=90°) the nanowire axis. (c) Testing setup for the polarization sensitivity measurement of our CNPD. (d) Normalized photocurrent of the CNPD as a function of the polarization angle θ; the unity corresponds to photocurrent when θ=90° or 270°.


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One unique feature of our OA-passivated CNPD is the linear dichroic photodetection. Though CH3NH3PbI3 has a symmetric crystal structure lacking intrinsic anisotropy, CH3NH3PbI3 nanowires exhibit external anisotropy due to their one-dimension geometry. The absorption capability of nanowires changes along with the intersection (polarization) angle (θ) between light polarization direction and nanowire axis, which results in polarization sensitive photoresponse. Finite difference time domain (FDTD) method44 was first applied to simulate the light absorption at different polarization angles. The relevant optical parameters of perovskite and quartz are adapted from references45,46. Since the length of CH3NH3PbI3 nanowire is much larger than its sectional dimensions, the periodic boundary conditions are applied in the x-axis to use infinite assumption as shown in Figure 5(a). Perfectly matched layer (PML) boundary conditions are applied in the y- and z- axis. The plane wave source with varied polarization angle θ illuminates above the nanowire toward the negative z direction. One simulation parameter is the height of nanowires and the width is set as 3 times the height based on the cross-section SEM and AFM results. The other simulation parameter is the wavelength of polarized light. Light absorption is defined as the square of electric field component intensity within the perovskite nanowires. Two kinds of situations (θ=0 and θ=90°) are chosen to describe obvious polarization dependent light absorption in Figure 5(b). The ratios of light absorption between θ=0 and θ=90°range from 0.8 to 2.6 depending on the incident light wavelength and nanowire height. According to our FDTD simulation, the highest polarization sensitivity is obtained when ~320 nm light illuminates on our CH3NH3PbI3 nanowire of ~200 nm height.

We measured the polarization sensitivity of our OA-passivated CNPD. Figure 5(c) displays the polarization test system which contains a LED emitting circularly polarized light at 530 nm, a


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collimating lens, a polarizer and a 45° reflector at the same altitude. The CNPD is subjected to polarized light illumination of perpendicular incidence. Along with one cycle rotation of the polarizer, incident light intensity is kept identical (confirmed as in Figure S7), but the photocurrent presents two cycles of sine fluctuation in Figure 5(d). The peaks of photocurrent are at θ=0, 180° and 360°, the angle where the light is polarized parallel to the CH3NH3PbI3 nanowire orientation axis, and the valleys are at θ=90° and 270°, the angle that the light is polarized perpendicular to the orientation axis. The peak-to-valley ratio of 1.3 showcases the strong polarization dependent detection of our CNPD, in good agreement with our FDTD simulation. In contrast, the perovskite film based photodetector shows no linear dichroic photodetection, as shown in Figure S7, a natural consequence of its crystal structure and geometric isotropy.

In summary, single-crystalline CH3NH3PbI3 nanowires were successfully prepared using onestep self-assembly method. SEM and AFM characterizations revealed its approximately rectangular cross section with the length up to 2 mm. HRTEM and SAED study confirmed the single-crystalline nature of these CH3NH3PbI3 nanowires. Of the three strategies explored, we found out that oleic acid passivation doubled the photocurrent, reduced by half the dark current and remarkably improved device stability. Photoluminescence and SCLC measurement indicated oleic acid passivation substantially reduced trap density, extended carrier lifetime and increased carrier mobility. As a result, our OA-passivated CNPD demonstrated sub-millisecond response time, 4.95 A/W responsivity, and measured detectivity of 2 × 1013 Jones, which is the highest measured detectivity reported so far for any photodetectors based on CH3NH3PbI3. By taking advantage of the anisotropic geometry of CH3NH3PbI3 nanowires, strong polarization dependent


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light detection of CNPD was realized for the first time, thus further expanding the potential application of organic-inorganic hybrid perovskite photodetectors. Experimental Section Formation of nanowires. All raw materials were purchased from commercial suppliers and used without any purification. Methylamine iodide (CH3NH3I) was synthesized using a mature method. The 1wt% precursor solution was prepared by dissolving equimolar PbI2 and CH3NH3I in DMF solvent. Glass substrates (size 1.5 × 1.5 cm) were washed in 120 ℃ piranha solution (1:3 volume ratio of hydrogen peroxide and sulfuric acid) for one hour, then soaked in deionized water for three times and dried by nitrogen gas flush, and finally treated by oxygen plasma for 10 minutes to improve its hydrophilicity. The glass substrate was tilted at a ~10° slope onto which 3 µL 1wt% precursor solution was dropped. Along with drying out of DMF, an array of CH3NH3PbI3 nanowires took shape from top to bottom. To improve the nanowire crystallinity, the product was heated at 70 ℃ for 10 minutes in ambient. Characterization of nanowires. The prepared CH3NH3PbI3 nanowires were characterized by scanning electron microscopy (SEM, Nova NanoSEM 450), atomic force microscopy (AFM, SPM 9700), transmission electron microscopy (TEM, Tecnai G20), X-Ray Diffraction (XRD, XRD-7000S/L), UV-vis absorption spectra (Cary, Lambda 950), and photoluminescence (PL, LabRAM HR800). The surface chemistry of OA on CH3NH3PbI3 nanowires was monitored by Flourier transform infrared spectroscopy (FTIR, VERTEX 70). Optoelectronic characterizations. All device performance characterizations were done in an optically and electrically sealed box to minimize electromagnetic disturbance. The monochromatic light source for photoresponse testing was a 530 nm LED (Thorlabs M530L3) modulated by a waveform generator (Agilent 33600A Series). For wavelength dependent


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photocurrent measurement, the spectrum was generated by modulating a bromine tungsten lamp using optical grating with a minimum interval of 10 nm. Dark currents, photocurrents and SCLC were measured using a semiconductor device analyzer (Agilent B1500A) by averaging the current over time for each voltage step. Noise currents were measured by using Stanford Research SR850 lock-in amplifier. Batteries were used to bias the device and special attention was paid to any possible electromagnetic interference to minimize external noise contribution. Since the resistance of our device was ~1011 Ω in dark state, it is impossible to buy commercial resistor with resistance in this range. We thus connected two apparently identical devices in series with one battery. One device acted as the sample while the other served as the standard resistance to input voltage signal to lock-in amplifier. The lock-in amplifier provided a scanning reference frequency to collect the frequency-dependent voltage signal. Through the choice of integration time, lock-in amplifier showed a noise voltage in V/Hz1/2. Then the noise voltage signal was used to calculate the frequency-dependent noise current in A/Hz1/2. The polarized optical system was made of a LED emitting at 530 nm, a collimating lens, a polarizer and a 45° reflector equipped at the same altitude.

ASSOCIATED CONTENT Supporting Information Figure S1 to S8 and detailed calculation of mobility, carrier density and trap density. This material is available free of charge via the Internet at http://pubs.acs.org.


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AUTHOR INFORMATION Corresponding Author * (J. T.) E-mail: [email protected] Author Contributions ‡ (L. G. and K. Z.) These authors contributed equally to this work. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the Major State Basic Research Development Program (2016YFB0700700 and 2016YFA0204000), and the Self-determined and Innovative Research Funds of HUST (2016JCTD111). We thank the Analytical and Testing Center of HUST and the Center for Nanoscale Characterization and Devices of WNLO for the characterization support. We also acknowledge Qianqian Lin for providing the refractive index and extinction coefficient of CH3NH3PbI3, Jingshu Guo and Jing Du for simulating the absorption of CH3NH3PbI3 nanowire via FDTD.

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Passivated Single-Crystalline CH3NH3PbI3 Nanowire Photodetector

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