文獻(xiàn)共享平板探測(cè)al2014materials

1、High-Performance Flexible Broadband Photodetector Based on Organolead Halide PerovskiteXin Hu, Xiaodong Zhang,* Lin Liang, Jian Bao, Shuang Li, Wenlong Yang, and Yi Xie*communication, wide spectral switches or memory storage through the use of single detector. During the light communication, in orde

2、r to improve the transmission rate and increase the transmission capacity, the wide spectrum photodetection is nec- essary. In the case of ultraviolet-visible light communication, the photodetectors can be used in the sunlight and other illu- mination light which is in our daily lives. By utilizing

3、the harmless characteristics of entire visible light, the visible photode- tector is expected to be a promising can- didate of high-power infrastructure for indoor/outdoor public ubiquitous data communication technology in the near future. So far, studies about photodetec- tors were mainly focused o

4、n their perfor- mances under special wavelength, due to the lack of proper materials which have the ability to absorb of incident radia- tion over broad wavelength range with1. IntroductionThe photodetectorsexcellent optoelectronic transfer efficiency. To expand thewavelength range of operation and

5、obtain the enhanced prop- erties, efforts have been devoted to design the photodetectors with wide spectral sensitivity through the combination of sev- eral different functional materials, which undergoes compli- cated fabrication process and requires expensive equipment (chemical vapor deposition,

6、thermal evaporation, and so on), thus drawing back their applications. For example, the carbon nanotube/TiO2 core-shell nanowires with broadband light- harvesting ability were grown through the atomic layer deposi- tion (ALD) method by controlling the TiCl4/H2O flow rate at0.25 Å/cycles after p

7、 eated carbon nanotube in the ALD reactor chamber.5 The expensive equipment and complicated fabrication processes will undoubtedly restrict their extensive applications. Thus, searching for proper materials with wide spectral sensitivity and easy assembly is urgently needed in the area of photodetec

8、tors.Bearing this in mind, we paid our attention to the hybrid organolead halide perovskites with a general formula of (RNH3) MX3 (R = CnH2n+1; X = halogen I, Br, Cl; M = Pb, Cd, Sn and so on), which have attracted signific nterests in electronicand photonic applications recently,611 owing to their

9、appro- priate direct bandgap,12 large absorption coefficient,13 long range balanced electron and hole-transport lengths,14,15 high electrical mobility,16,17 and so on. Furthermore, the series of (RNH3)MX3 perovskites can be fabricated by a simple and cost- effective solution-based self-assembly meth

10、od, rendering the (RNH3)MX3 to be a competitive candidate for the applicationwhich can convert incident light (ultra-violet, visible or infrared) into electrical signal are critical for a variety of industrial and scientific applications, includingoptical communications, environmental monitoring, da

11、y- and night-time surveillance and chemical/biological sensing.14 Generally speaking, the photodetecors can be mainly devided into two type of sub-systems: special wavelength detector (ultraviolet detector, visible or infrared detector) and broad- band detector, according to the wavelength range of

12、operation. The special wavelength photodetectors are required under cer- tain single wavelength light or the light with a narrow range, showing specific applications in light detecting and nano-opto- electronic integrated circuits. In comparison, the broadband photodetectors can detect the spectral

13、ranges from ultraviolet to infrared and meet the demands on ultraviolet-visible light Dr. X. Hu, Dr. X. Zhang, Dr. L. Liang, Dr. J. Bao, Dr. S. Li, Dr. W. Yang, Prof. Y. XieHefei National Laboratory for Physical Science at MicroscaleCollaborative Innovation Center of Chemistry for Energy MaterialsUn

14、iversity of Science and Technology of Hefei, Anhui 230026, P. R.: zhxid; yxieDOI: 10.1002/adfm.2014020207373Adv. Funct. Mater. 2014, 24, 73737380© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimFULL PAPEROrganolead halide perovskites have attracted extensive attentions as light harvesting m

15、aterials for solar cells recently, because of its high charge- carrier mobilities, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Herein, with CH3NH3PbI3 film deposited on flexible ITO coated substrate, the first organolead halide perovskite based broadband photod

16、etector is demonstrated. The organolead halide perovskite photode- tector is sensitive to a broadband wavelength from the ultraviolet light to entire visible light, showing a photo-responsivity of 3.49 A W-1, 0.0367 A W-1, an external quantum efficiency of 1.19´103%, 5.84% at 365 nm and 780 nm

17、with a voltage bias of 3 V, respectively. Additionally, the as-fabricated photo- detector exhibit excellent flexibility and robustness with no obvious varia- tion of photocurrent after bending for several times. The organolead halide perovskite photodetector with high sensitivity, high speed and bro

18、ad spec- trum photoresponse is promising for further practical applications. And this platform creates new opportunities for the development of low-cost, solution- processed and high-efficiency photodetectors.Figure 1. a) Three-dimensional schematic representation of perovskite structure of CH3NH3Pb

19、I3. The image was produced using VESTA software.41b) XRD pattern of the MAPbI3. c) The image of semitransparent MAPbI3 thin films with different thickness. d) UVVis absorption spectrum of MAPbI3 film.in a plenty of electronic devices.18 Despite extensive researchesthe organic components (CH3NH3)+ in

20、 12-fold cuboctahedral coordination. The significant hybridization between the Pb-6s and the I-5p states are formed in the polyhedron of PbI6/2-.20 In this work, the MAPbI3 film was prepared by drying 40 wt% of MAPbI3/g-butyrolactone solution in air at room temperature and was characterized by X-ray

21、 diffraction (XRD) and ther- mogravimetric analysis (TGA), as shown in Figures 1b and S1, respectively. The XRD of as-deposited film has two main peaks at 14.00° and 28.36°, which can be ily indexed to the(110) and (220) planes of the tetragonal perovskite structure (a = 8.855 Å and c

22、 = 12.659 Å).21 The TGA spectrum shows that the perovskite crystal is thermally stable up to 300 ºC, but quickly decomposes above this temperature due to the decom- position of the MAI component with a mass loss of 25.7%. Thetypical magnification SEM image of MAPbI3 sample deposited on the

23、 flexible indium tin oxide (ITO)-coated polyethylene tere- phthalate (PET) sheet is shown in Figure S2a. The thin films with different thickness can be easily controlled by varying the volume of 20% MAPbI3/g-butyrolactone dilute solution,resulting in tunable and semitransparent film of MAPbI3 (Figur

24、e 1c). In addition, the film of MAPbI3 can also be easily formed on various rigid and flexible substrates, including Si, SiO2, glass, PET and so on. As displayed in the UVVis absorp- tion spectra of Figure 1d, the MAPbI3 film shows a wide absorp- tion spectrum, indicating high light-harvesting capab

25、ilities over the ultraviolet to visible spectrum.As schematically illustrated in Figure 2a, the MAPbI3 basedphotodetector was fabricated by depositing MAPbI3 film on a flexible ITO/PET substrate with the bridging-gap width of about 15 µm and length of 1 cm, respectively. In order todone,1215on

26、the application of optical devices have beenstudies on the design and fabrication of photodetector based on (RNH3)MX3 film have not been reported so far.Herein, by depositing CH3NH3PbI3 (MAPbI3) film on flexible substrate, the first organolead halide perovskite based broad- band photodetector is dem

27、onstrated. Because of the optimum bandgap and large absorption coefficient,12 the MAPbI3 can be sensitive to a wide spectra wavelength from ultraviolet to visible light, which is desirable for the design of broadband photodetector. In order to study the performance of MAPbI3 film photodetector syste

28、matically, the spectrum of 365 nm and 780 nm are selected as representatives. The as-designed photo- detectors have a high photo-to-dark current ratio, fast response speed, excellent stability and reproducibility. Our results not only demonstrate the uniqueness and effectiveness of MAPbI3 for photod

29、etection applications, but also provide a simple and low-cost method applicable for broadband light optical sensor production.2. Results and Discussion2.1. Synthesis and Structural AnalysisThe MAPbI3 has a distorted three-dimensional perovskite struc- ture that crystallizes in the tetragonal I4/mcm

30、space group at room temperature as schematically illustrated in Figure 1a.19 The structure consists of lead cations in 6-fold coordination, surrounded by an octahedron of halide anions together with7374© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimAdv. Funct. Mater. 2014, 24, 73737380FUL

31、L PAPERFigure 2. a) Schematic illustration of the MAPbI3 film photodetector. b,c) Photocurrent response of the photodetector to monochromatic light in the ultraviolet and visible range. The light intensity is 0.01 mW cm-2. d) Spectral photoresponse of MAPbI3 film device at different wavelengths from

32、 310 nm to 780 nm at a bias of 3V.clearly illustrate the structure of the device, we have added the ed schemes of the photodetector and the correspondingSEM images in Figure S3. The two adjacent ITO film is employed as conductive electrodes with the bridging MAPbI3 film between them. The bridging-ga

33、p is filled with MAPbI3 film and the thickness of the film is measured ca.1.5 µm (Figure S2b). The influence of ITO/PET substrate to the pho- toresponse has been excluded by the comparison experiments (Figure S4). To benchmark the performance of photodetector,two key criteria were measured: spe

34、ctral responsivity (Rl) andexternal quantum efficiency (EQE). The spectral responsivity (Rl) can be defined as Rl = DI/PS, where DI (D I = Iphoto Idark) is the difference between the photocurrent and dark current, P is the incident light intensity, and S is the effective illumi- nated area.22 Figure

35、s 2b and 2c are the photocurrent response at different wavelengths from 310 to 780 nm (0.01 mW cm-2) as a function of biasing voltage (applied across the film). The full I-V sweeps were shown in Figure S5. From the MAPbI3 film device as shown in Figure 2a, based on the values ofDI = 0.52283 µA

36、(Figure 2c) and S = 1.5 ´ 10-7 m2, the Rl of the photodetector irradiated by 365 nm light at 0.01 mW cm-2 is3.49 A W-1, under the bias voltage of 3 V. As shown in Figure 2d, the spectral photoresponse of the flexible photodetector clearly demonstrated the responsivities of this device range fro

37、m 0.2 to 7.0 A W-1, which are expected values of the light source and the monochromator from specifications, showing a broadbandphotodetection characteristic. The sharp increase of the spectral photoresponse below 400 nm, which is possibly attributed to the different concentration of the excited ele

38、ctron-hole pairs gener- ating under various wavelength of lights. It is well known that the photoconduction is due to the electron-hole pairs excited bythe incident light with energy larger than the band gap, only light with enough photon energy is able to induce a significant increase in conductanc

39、e. Light with a larger energy in the short wavelength can excite more electrons from the valence band to the conduction band and thus contributes more to the photo- current. The transition probability increases for higher photon energies, which is reflected in the monotonous increase of the photocur

40、rent down to a 400 nm excitation wavelength.23 For our device, the electrons have to overcome the Schottky bar- rier during transporting. Light with a larger energy in the short wavelength can excite more electrons from the valence band to the conduction band and thus contributes more to the photo-

41、current. As a result, the built-in potential of the Schottky barrierdecreases, resulting in a large increase incarrier density,leading to the easier carriers transport and tunnelling, thus,to a greatly enhanced photocurrent of the MAPbI3 devices. It is worth noting that this is a common phenomenon i

42、n other broadband photodetectors, such as hybrid phenyl-C61-butyric acid methyl ester/Cd3P2 nanowire24 with ultraviolet-visible- near infrared photodetecting ability, the monolayer MoS2nm),23photodetector with ultrasensitive broadband (< 680the UVVisible photodetector of atomically thin GaSe nano

43、sheet25 and the UVVisible photodetector of ultrathin GaS nanosheet.26 The broad photoresponse is also supported by the external quantum efficiency (EQE) spectrum. The EQE is defined as the number of electrons detected per incident photon and is expressed by the relationship: EQE = hcRl/el, where h i

44、s Plancks constant, c is the velocity of light, e is the elec- tronic charge and l is the exciting wavelength.27 In Figures 2b and 2c, the EQE of the MAPbI3 film photodetector (at 3 V,0.01 mW cm-2) was calculated to be 1.19 ´ 103 % at 365 nm7375Adv. Funct. Mater. 2014, 24, 73737380© 2014 W

45、ILEY-VCH Verlag GmbH & Co. KGaA, WeinheimFULL PAPERand 5.84% at 780 nm, respectively. The performance data of Rl and EQE of MAPbI3 based photodetector are about 103 times higher than that of graphene (1 ´ 10-3 A W-1, 616%),28 gra- phene oxide (4 ´ 10-3 A W-1, 0.3%)29 and single-layer M

46、oS2 (7.5 ´ 10-3 A W-1),30 due to an efficient adsorption of photons for MAPbI3. Nowadays, although some broadband photodetec- tors with nanowires and nanotubes have been demonstrated, their practical applications in high yield and scalable systems face formidable problems in assembly and manufa

47、cture. Mate- rials with solution-based self-assembly can effectively avoid these limitations since they are compatible with established device designs and processing approaches in the semiconductor industry. All of these results demonstrate that the MAPbI3 film can be used in highly sensitive photod

48、etectors and fast photo- electric switches.devices during repeated switching of 365 nm light illumination at the bias of 1, 2, 5 and 8 V, respectively. The current of the photodetector reaches 17.50 µA under a high power irradia- tion of 0.13 mW cm-2, producing a photocurrent on/off ratio of 32

49、4 with a bias of 8 V. A peak photoresponse current of 0.76 µAand an on/off current ratio of 152 can also be achieved, even at a lower bias of 1 V. The above results have shown that the MAPbI3 photodetector can achieve high sensitivity and perfor- mance for a low-intensity optical signal. This i

50、s a particularly attractive attribute for low-power optoelectronic applications.Repeatability and response speed are the key parameters to determine the capability of a photodetector. However, it is still a challenge to achieve photodetectors with both high repeatability and fast temporal response u

51、p to date. Figure 3b shows the photocurrent of the flexible devices during repetitive switching of light illumination, or on/off switching. No obvious degrada-tion is detected for aage photocurrent of 0.25 µA over2000 s, indicating the excellent photocurrent stability of the MAPbI3 based sensor

52、. The inset of Figure 3b is the enlarged portion of 20100 s range. For the application of photodetec- tors, a fast response and recovery speed are commonly desired characters. Herein, the rise time and decay time of the pho- todetector are defined as the time taken for the initial current to increas

53、e to 90% of the peak value, or vice versa. Figure 3c2.2. Flexible MAPbI3 Film Photodetector Under 365 nm Light IlluminationTo study the light response ability of the device, we explored its photosensitivity dependence on light intensity. As shown in Figure 3a, the currentvoltage (I-V) curves of the

54、device have been measured in the dark and under illumination with 365 nm light at different power intensities from 0.01 to0.21 mW cm-2. Under light illumination, the photocurrent ofthe devices increases drastically, particularly at high voltage bias, demonstrating a nonlinear and asymmetrical I-V be

55、havior. The result indicates that a Schottky contact is formed. The Schottky contact might be attributed to the influence of theshows the moreed transient photocurrent of this devicefrom Figure 3b. The rise time and decay time are both shorter than 0.2 s. The high stability and fast response of the

56、device are promising for large-area photodetector applications.surface state (including surface defects, vaces and adsorp-2.3. Flexible MAPbI3 Film Photodetector Under 780 nm Light Illuminationtion) of the devices and the metal/semiconductor interface.31At the same voltage, the light current increas

57、es gradually with the increasing of light intensities, which can be attributed to a change in the photon intensity from the incident light. A high current of 0.26 µA was recorded at an applied voltage of 3 V when the device was illuminated with 365 nm light at a very low power intensity of 0.01

58、 mW cm-2, demonstrating the ultimate high sensitivity of the MAPbI3 film photodetector. The intensity dependence of the photocurrent can be fitted by the power law I P0.44, where I is the photocurrent and P is the light inten- sity, as shown in Figure S6a. The photoswitching characteristicand stability of the flexible photodetector were investigated at room temperature in air. As shown in Figure S6b, the photo- current as a function of time was measured during repetitive switching of 365 nm light illumination, under the alternative dark and illumination conditions at a different bia