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Stable, High-Sensitivity and Fast-Response Photodetectors Based on Lead-Free Cs 2 AgBiBr 6 Double Perovskite Films
Jie Yang, Chunxiong Bao, Weihua Ning, Bo Wu, Fuxiang Ji, Zhibo Yan, Youtian Tao, Jun-Ming Liu, Tze Chien Sum, Sai Bai,* Jianpu Wang, Wei Huang, Wenjing Zhang,*
and Feng Gao*
DOI: 10.1002/adom.201801732
large light absorption coefficients, long carrier diffusion lengths, and high carrier mobility, which make them promising semiconductors for the fabrication of photodetectors with high sensitivity and fast response speed.[4–13] Despite the great advances, the intrinsic material instability and the toxicity issue of the commonly used lead halide perovskites hinder their practical applications.[14–16]
Recently, alternative bismuth (Bi) or tin (Sn) based lead-free halide perovskites have been explored for the photodetector applications.[17–19] However, all the reported lead-free perovskite photodetectors show slow response time of milliseconds and poor detect- able light intensity of ≈µW cm−2, which still fall behind those based on the well- investigated lead-based perovskites.[6,10,11]
In addition, most of the reported lead-free perovskites exhibit poor material stability and/or low charge transport properties, which further hinder their applications in efficient and stable photodetectors.
As a new generation of semiconductors, lead-free double halide perovskites, which exhibit superior material stability and photoelectric properties are ideal for efficient and environmental-friendly optoelectronic applications.[20–27]
For example, Tang and co-workers have demonstrated high- performance X-ray detectors with low detection limit based on Solution-processed metal halide perovskites (MHPs) have demonstrated
great advances on achieving high-performance photodetectors. However, the intrinsic material instability and the toxicity of lead still hinder the practical applications of MHPs-based photodetectors. In this work, the first highly sensitive and fast-response lead-free perovskite photodetectors based on Cs2AgBiBr6 double perovskite films are demonstrated. A
convenient solution method is developed to deposit high-quality
Cs2AgBiBr6 film with large grain sizes, low trap densities, and long charge carrier lifetimes. Incorporated within a photodiode device architecture comprised of optimized hole- and electron-transporting layers, lead- free perovskite photodetectors are achieved exhibiting a high detectivity of 3.29 × 1012 Jones, a large linear dynamic range of 193 dB, and a fast response time of ≈17 ns. All the key figures of merit of the devices are comparable with the reported best-performing photodetectors based on lead halide perovskites. In addition, the resulting devices exhibit excellent thermal and environmental stability. The nonencapsulated devices show negligible degradation after thermal stressing at 150 °C and less than 5% degradation in the photoresponsivity after storage in ambient air for ≈2300 h. The results demonstrate the great potential of the lead-free Cs2AgBiBr6 double perovskite in applications for environmentally friendly and high-performance photodetectors.
Dr. J. Yang, Dr. C. Bao, Prof. W. Zhang
International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology
Shenzhen University Shenzhen 518060, China E-mail: [email protected]
Dr. J. Yang, Dr. C. Bao, Dr. W. Ning, F. Ji, Dr. Z. Yan, Dr. S. Bai, Prof. F. Gao
Department of Physics, Chemistry, and Biology (IFM) Linköping University
Linköping SE-58183, Sweden
E-mail: [email protected]; [email protected] Perovskite Photodetectors
The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.201801732.
Dr. W. Ning, Prof. Y. Tao, Prof. J. Wang, Prof. W. Huang
Key Lab for Flexible Electronics and Institute of Advanced Materials Jiangsu National Synergistic Innovation Center for Advanced Materials (SICAM)
Nanjing Tech University
30 South Puzhu Road, Nanjing 211816, P. R. China Dr. B. Wu, Prof. T. C. Sum
Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University (NTU)21 Nanyang Link
Singapore 637371, Singapore Dr. Z. Yan, Prof. J.-M. Liu
Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures
Nanjing University Nanjing 210093, P. R. China High-performance photodetectors are key components in
many important optoelectronic applications, such as optical communications, imaging, and photon detection.[1–3] Solution- processed metal halide perovskites (MHPs) have demonstrated
www.advancedsciencenews.com www.advopticalmat.de Cs2AgBiBr6 double perovskite single crystals.[25] Sensitive and
fast ultraviolet (UV) photodetectors based on Cs2AgInCl6 single crystals with low trap density have also been reported.[20] How- ever, due to the different solubility of the raw materials in the common organic solvents, cost-effective solution-processing for the fabrication of high-quality double perovskite thin films has been limited and the related optoelectronic devices are rarely reported.[28–31]
Recently, through employing carefully chosen organic solvent or well-controlled vacuum-assisted processing, uniform Cs2AgBiBr6 double perovskite thin films have been fabri- cated and integrated into photodetectors.[21,22] However, the resulting devices with a metal–semiconductor–metal (MSM) or heterojunction device structure exhibit low sensitivity and slow response speed, which are mainly due to the large trap density in the perovskite active layer and the nonoptimized device structures. In our previous report, we have developed a novel solution-processing method for the deposition of high-quality double perovskite thin films from Cs2AgBiBr6 single crystal- based precursor solution. The fabricated thin films exhibit long and balanced charge carrier diffusion lengths, leading to effi- cient solar cells with superior stability.[24] However, the films still consist of abundant grain boundaries due to the relatively small crystal grain sizes, which induce non-negligible defects and limit their applications in high-sensitivity and fast-response photodetectors.
In this work, we successfully fabricate high-crystallinity Cs2AgBiBr6 films with enlarged grain sizes and reduced trap densities through optimizing the solution-processing method.
We further optimize the electron and hole transport interlayers and achieve the first high-sensitivity and fast-response lead-free perovskite photodetector. The resulting devices exhibit a lowest detectable limit of tens of pW cm–2 and an ultrafast response time of ≈17 ns, both of which are comparable to the best- performing photodetectors based on lead halide perovskites.
More importantly, the Cs2AgBiBr6 double perovskite-based photodetectors exhibit superior environmental and device oper- ational stability. For the nonencapsulated devices, we observe negligible degradation in the device performance under thermal stressing at a high temperature of 150 °C and ≈ 94%
of the initial photoresponsivity can be retained after storage in ambient air for ≈ 2300 h.
We synthesize the Cs2AgBiBr6 double perovskite single crys- tals following the developed method in our previous report.[24]
We prepare and optimize the precursor solution using a mixture of N,N-dimethylformamide (DMF) and dimethyl sul- foxide (DMSO) as the solvent for the single crystals. We find that the incorporation of a small amount of DMF is helpful to enlarge the grain size of the obtained Cs2AgBiBr6 films.
Figure 1a–d shows the top-view scanning electron microscope (SEM) images of the Cs2AgBiBr6 double perovskite films pro- cessed from DMSO-based precursors containing 0%, 5%, 10%, and 20% of DMF v/v (marked as 0% DMF, 5% DMF, 10%
DMF, and 20% DMF). The Cs2AgBiBr6 film fabricated from pure DMSO solution exhibits small crystals with an average size of ≈ 250 nm. As the DMF ratio increases to 10%, larger grains with the size of over 1 µm appear in the obtained films (Figure 1b,c). The results are in good agreement with the obviously increased intensity of the main diffraction peaks of
(200) and (400) at 15.71° and 31.76° from the XRD patterns (Figure 1e), suggesting the improved crystallinity or orienta- tion of the obtained double perovskite films. As we observe much worse solubility of the double perovskite single crystals in DMF (Figure S1, Supporting Information), we anticipate that the introduced DMF reduces the nucleation sites and promotes the Ostwald ripening of the crystals during the film formation, which is consistent with previously demonstrated crystal growth process of lead halide perovskites.[32] We observe the appearance of some bright areas from the SEM images when we further increase the DMF ratio to 20% (Figure 1d). We attribute these to the formation of impurity phase of Cs3Bi2Br9 according to the XRD characterization results which show a new diffraction peak located at 12.7°.[29,33] Figure S1 in the Supporting Infor- mation shows that the solubility of AgBr in the DMF/DMSO (20%) solvent is much lower compared with that of CsBr and BiBr3. As a result, the introduced excess DMF may change the stoichiometric molar ratio of CsBr:AgBr:BiBr3 in the precursor solution, inhibiting the AgBr to fit within the crystal lattice and resulting in the formation of Cs3Bi2Br9 impurity. We find no obvious changes to the absorption spectra of the resulting films (Figure S2, Supporting Information). However, we do observe significantly increased photoluminescence (PL) intensity (Figure S3a, Supporting Information) and longer PL lifetime (Figure 1f) for the 10% DMF film, suggesting the reduced trap densities in the resulting double perovskite films, consistent with the enlarged grain size and improved film crystallinity from the SEM and XRD results.
We further investigate the effects of charge transport inter- layers on the device performance of the photodetectors. We choose a photodiode device structure with both electron- and hole-transporting layers (HTL) (Figure 2a), which has been dem- onstrated efficient in reducing the dark current and improving the response speed of the photodetectors.[6,11] The commonly used n-type metal oxides (TiO2 and SnO2) and p-type organic materials of 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)- 9,9′-spirobifluorene (spiro-OMeTAD) and poly[(9,9- dioctylfl uorenyl-2,7-diyl)-co-(4,4′-( N-(4-sec-butylphenyl) diphenylamine)) (TFB) are studied. When the spiro-OMeTAD is used as the HTL, we measure obviously high dark currents for devices on both TiO2 and SnO2 electron-transporting layer (ETL) (Figure 2b). In contrast, the devices with TFB as the HTL exhibit significantly lower dark current under the same bias condition. We measure a dark current of 1.0 × 10−4 mA cm−2 at
−0.2 V for devices processed on the SnO2 substrate with TFB as the HTL, which is much lower than previously reported MSM devices and is comparable with the well-investigated lead-based perovskite photodetectors.[9,10] Considering the same active layer thickness and absorption (Figure S2, Supporting Information) and the similar energy level structures (Figure S4, Supporting Information) of the charge transporting interlayers in the device structures, we anticipate that the observed dif- ference in the dark current may origin from the different trap densities in the devices.
In order to obtain further information on the trap densities, we perform capacitance spectra measurement of the devices with different charge transporting interlayers. The difference of the capacitance at different frequencies reflects the elec- trical active defect state properties of the Cs2AgBiBr6 films.[34]
Figure 2c shows the measured capacitance results of the three devices at 300 K. The measured capacitance at low and high frequency of devices with spiro-OMeTAD as HTL are much larger than those of devices with TFB as the HTL, indi- cating more serious trap states with spiro-OMeTAD HTL. We further conduct the capacitance measurements at different tem- peratures to reveal the trap density distribution in the devices (Figure S5, Supporting Information). Based on the characteri- zation results, trap density of state (tDOS) of the devices with different structures can be calculated as shown in Figure 2d.[34,35] The tDOS of the devices with spiro-OMeTAD as the HTL are ≈1022 and ≈1023 m−3 eV−1 based on SnO2 and TiO2, respectively, which suggests that there may exist more defects at the interfaces of double perovskite/TiO2. Further replacing the spiro-OMeTAD with TFB, the tDOS decreases by nearly two orders of magnitude. This is a surprising result, which indicates
that the TFB is likely to introduce a further passivation of the defects at the surface of the obtained double perovskite films, which is consistent with the previously demonstrated passiva- tion effects of TFB for lead-halide perovskites.[36]
Having established the optimized device structure, we now evaluate the key device parameters of the Cs2AgBiBr6 double perovskite photodetectors with the SnO2 and TFB as the ETL and HTL, respectively. Figure 3a and Figure S7a in the Sup- porting Information show the photocurrent and dark J–V curves for Cs2AgBiBr6 photodetectors fabricated with 0%, 5%, 10%, and 20% DMF. We observe that the addition of DMF in precursor solution plays a crucial role in enhancing the photocurrent, with the highest short-circuit current (JSC) of 1.1 mA cm−2 for photodetector processed from 10% DMF. The result is further evidenced by the measured higher external quantum efficiency (EQE) measured at 0 V bias (Figure 3b Figure 1. a–d) Scanning electron microscope (SEM) images of the Cs2AgBiBr6 films fabricated from solutions containing different DMF ratio of 0%, 5%, 10%, and 20%. e) X-ray diffraction (XRD) patterns of Cs2AgBiBr6 films fabricated from solutions containing different DMF ratio of 0%, 5%, 10%, and 20%. The peak marked with diamond for the 20% XRD pattern indicates the side phases Cs3Bi2Br9 (international centre for diffraction data (ICDD) No. 01-070-0493). Peaks marked with inverted triangles belong to ITO substrates. f) Time-resolved photoluminescence (TRPL) of the Cs2AgBiBr6 films fabricated from solutions without and with 10% DMF.
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and Figure S7b, Supporting Information), which we attribute to the better crystallinity and reduced trap density of the double perovskite active layer. The optimized device shows a small dark current noise of ≈10 fA Hz−1/2 at high frequency at 0 V bias (Figure 3c), while the instrument noise current is around 2 fA Hz−1/2, which demonstrates that the measured noise is mainly from the device. Based on the EQE curves and the device noise current at high frequency, we calculate the device responsivity (R) and specific detectivity (D*) according to the following calculations
EQE 1240
ph light
R J
L
= = ⋅λ
λ (1)
*
n
D R AB
= λi (2)
where Jph is the photocurrent, Llight is the incident light intensity, EQE is the external quantum efficiency of the photodetector, λ (nm) is the wavelength of incident light, in
is the dark current noise of the device, A is the devices area, and B is the bandwidth. The values were calculated to be 0.14 A W−1 and 3.29 × 1012 Jones at 445 nm, which we plot in Figure 3d. The noise current which is used to determine the detectivity is the measured lowest noise current at 655 Hz frequency. We note that the detectivity of our optimized device surpasses all the lead-free perovskite photodetectors.[15,17–20]
In addition, it is also comparable to the devices based on lead
halide perovskites[6,11] and the commercial Si photodiode at the same wavelength, demonstrating its potential application in the detection of UV and blue light.
We now investigate the linear dynamic range (LDR), which is an important characteristic for the photodetector and can be used to determine the detectable light intensity range. We calculate the LDR of our devices based on the linearly detectable light intensity or linear photocurrent.
LDR 20lg max 20lg
min
max min
P P
J
= = J (3)
where the Pmax (Pmin) is the maximum (minimum) light inten- sity that a photodetector can linearly response to, the Jmax (Jmin) is the maximum (minimum) linear response photocurrent of a photodetector. The photocurrent of the device as a function of the light intensity is provided in Figure 3e. We observe that our optimized photodetectors based on the Cs2AgBiBr6 double perovskite show a linear response range from a light inten- sity of 2 × 10−11 to 0.15 W cm−2, corresponding to a large LDR of 193.4 dB. This value compares favorably with that of the best-performing lead halide perovskite photodetectors based on CH3NH3PbI3−xClx thin film (>100 dB) or CH3NH3PbI3 single crystals (222 dB) and even larger than the commercially available Si (120 dB) or InGaAs based (66 dB) photodetectors.
We further study the response speed of the double perov- skite photodetectors by measuring the transient photo current when applying a 4 ns wide pulse laser (337 nm) to excite Figure 2. a) Schematic structure of the photodiode type photodetector with Cs2AgBiBr6 as light absorber layer. b) Dark current density–voltage curves of the Cs2AgBiBr6 photodetectors based on different charge transporting layers with Cs2AgBiBr6 fabricated from solution with 10% DMF. c) Capacitance spectra of Cs2AgBiBr6 photodetectors based on different charge transporting layers and double perovskite films fabricated from solution with 10% DMF. d) Trap density of Cs2AgBiBr6 photodetectors based on different charge transporting layers and double perovskite films fabricated from solution with 10% DMF.
the photodetectors. Figure S8a in the Supporting Informa- tion shows the transient photocurrent curves of the double perovskite photodetectors fabricated with perovskite precursor with different DMF ratio. By fitting the decay curves with the exponential decay function, the response time of the devices are obtained. A fastest response speed of about 164 ns can be obtained for the optimized device based on the 10% DMF film.
The response speed of the double perovskite photodetectors based on different charge transporting layers is also compared, which are given in Figure S8b in the Supporting Information.
The Cs2AgBiBr6 photodetectors with TiO2/spiro-OMeTAD and SnO2/spiro-OMeTAD as charge transporting layers show large response time over 1 µs, while the devices with TFB HTL show much faster response time of ≈ 200 ns. It has been demon- strated that the resistance-capacitance constant, which is related to the defects in the devices, is a crucial factor determining the response speed of a photodetector.[7,11] As a result, the fastest
response speed is observed for the optimized devices based on perovskite film fabricated with DMF ratio of 10% and SnO2/ TFB charge transporting layers. Meanwhile, a further improved response speed is obtained based on smaller-area devices, which is consistent with the decreased devices capacitance. As shown in Figure 3f, an ultrafast response speed of ≈ 17 ns can be obtained for a device with an active area of ≈0.2 mm2, which represents the fastest lead-free perovskite photodetector and is comparable with the best-performing lead-based perovskite photodetectors reported so far (as shown in Table 1).[11,20–22]
Finally, we proceed to investigate the device operational stability, which is critically important for practical applications of the photodetectors. We first study the device operational stability of the Cs2AgBiBr6 photodetectors by monitoring the change of the photocurrent at different temperature under illumination with a blue light emitting diode (LED) light. The devices are placed on a hot plate in ambient air condition (T: 20 °C, relative Figure 3. a) Current density–voltage (J–V) curves of the Cs2AgBiBr6 photodetectors fabricated with DMF ratio of 10% under dark and AM 1.5 illumination.
b) EQE curves at 0 V bias of the Cs2AgBiBr6 photodetectors fabricated from solution with DMF ratio of 10%. c) Noise current at 0 V bias of the Cs2AgBiBr6 photodetectors fabricated from solution with 10% DMF and instrument noise current. d) Responsivity and detectivity at 0 V bias of the Cs2AgBiBr6 photodetectors fabricated from solution with 10% DMF. e) LDR of the Cs2AgBiBr6 photodetectors fabricated from solution with 10% DMF measured under a 450 nm light illumination. f) Transient photocurrent at 0 V bias of the Cs2AgBiBr6 photodetectors with different active area from 7.25 to 0.2 mm2.
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humidity (RH): ≈40%) without encapsulation. A CH3NH3PbI3 (MAPbI3) photodetector with the same device structure is inves- tigated simultaneously as a control for the stability comparison.
As we show in Figure 4a of the device stability performance, the photocurrent of the Cs2AgBiBr6 photodetector keeps con- stant in the initial 1 h operational test at room temperature, while the MAPbI3 photodetector experiences slow degradation, indicating a better stability of Cs2AgBiBr6 device under 450 nm illumination in ambient with light intensity of 10 µW cm−2. We then increase the temperature of the hot plate to 150 °C and keep measuring the devices for another 1 h. We discover that the photocurrents of both photodetectors quickly decrease to about half of the initial values (Figure 4a), which is prob- ably due to the increase of nonradiative recombination in the semiconductors at a high temperature.[37] The photocurrent of Cs2AgBiBr6 photodetectors becomes steady in about 20 min after the temperature increase to 150 °C, while a continuous decay is observed for MAPbI3 photodetectors. After we cool the hot plate to room temperature, the photocurrent of Cs2Ag- BiBr6 photodetectors goes back to its original value. However, the MAPbI3 photodetectors shows nonreversible degradation in the device performance, which is due to the well-known decomposition of the MAPbI3 active layer at elevated tem- perature.[38,39] The results suggest superior thermal stability of the Cs2AgBiBr6 double perovskite active layer and the resulting photodetectors. The actual current values are given in Figure S9 in the Supporting Information. We also investigate the long- term device operational stability in ambient air under light illumination for 10 h and show the results in Figure 4b. We observe that the Cs2AgBiBr6 double perovskite photodetectors show almost constant device performance during the whole test. We further demonstrate the great environmental stability of the obtained double perovskite devices (18 devices), with 94% of its initial photoresponsivity retained after storing under ambient condition (RH: ≈40%) for 2300 h (Figure 4c).
In summary, we have demonstrated the first high-sensitivity and fast-response lead-free perovskite photodetectors based on high-crystallinity Cs2AgBiBr6 double perovskite with an opti- mized photodiode device structure. The resulting devices exhibit a high specific detectivity of 3.29 × 1012 Jones, a high linear dynamic range of 193 dB, and a fast response time of ≈17 ns,
representing the best-performing lead-free perovskite photodetec- tors so far. Moreover, we demonstrated the superior operational, thermal, and environmental stability of the resulting devices, suggesting the great advances of the Cs2AgBiBr6 double perov- skite photodetectors for the applications under harsh conditions.
Experimental Section
Materials: All the materials were used as received without further purification. The materials used in our work are as follows: 15% SnO2 colloid precursor (Alfa Aesar), 97% titanium isopropoxide (Sigma- Aldrich), CsBr (99.9%, Alfa Aesar), AgBr (99.999%, Sigma-Aldrich), BiBr3 (≥98%, Sigma-Aldrich), 47% HBr aqueous solution, anhydrous DMSO (Sigma-Aldrich), anhydrous DMF (Sigma-Aldrich), TFB (poly(9,9-dioctyl- fluorene-co-N-(4-butylphenyl)diphenylamine), Sigma-Aldrich), spiro- OMeTAD (Sigma-Aldrich), Li-TFSI (lithium bis(trifluoromethanesulfonyl) imide, Sigma-Aldrich), tert-butylpyridine (96%, Sigma-Aldrich).
Cs2AgBiBr6 Single Crystals Synthesis: 213 mg CsBr, 225 mg BiBr3, and 94 mg AgBr were added in 8 mL of 47% HBr aqueous solution. The mixture was heated to 120 °C until the materials were totally dissolved. Then the solution was cooled to room temperature slowly (in ≈12 h). Red Cs2AgBiBr6 octahedral single crystals can be obtained with size up to 4 × 4 × 2 mm3.
Photodetectors Fabrication: The SnO2 film precursor solution was prepared by diluting 15% (wt%) SnO2 nanocrystal colloidal solution (Alfa Aesar) in deionized water to 2.67% (wt%). SnO2 precursor solution was spin coated onto an indium tin oxide (ITO) substrate at 4000 rpm for 30 s, followed by annealing at 150 °C for 0.5 h. 0.5 m Cs2AgBiBr6
precursor solution was prepared by dissolving the Cs2AgBiBr6 single crystals in DMSO/DMF mixed solvents at 150 °C with the DMF ratios of 0%, 5%, 10%, and 20%, respectively. The time of dissolving depends on the amount of DMF in the solution. For 5%, 10%, and 20% DMF, the single crystals dissolving time is about 2, 5, and 8 min, respectively.
After the solution cooled down to room temperature, Cs2AgBiBr6 films were deposited onto the SnO2/ITO substrates at 4000 rpm for 60 s and annealed at 250 °C for 10 min to obtain better crystallization. The TFB precursor solution was prepared by dissolving 12 mg TFB in 1 mL chlorobenzene. The TFB hole transporting layer was spin coated on the Cs2AgBiBr6 films at 3000 rpm for 30 s. Finally, a 7 nm MoO3 layer and an 80 nm gold layer were deposited by thermal evaporation at a pressure of 1 × 10−4 mbar. TiO2 compact layers were fabricated by spin-coating an acid titanium isopropoxide ethanol solution at 5000 rpm for 20 s, followed by annealing at 200 °C for 2 h. Spiro-OMeTAD hole transporting layer was fabricated by spin-coating a chlorobenzene solution (72.3 mg spiro-MeOTAD, 17.5 µL Li-TFSI in acetonitrile (520 mg mL−1), and 28.8 mL tert-butylpyridine in 1 mL chlorobenzene) at 3000 rpm for 30 s.
Table 1. Summary of the key device parameters of literature reported perovskite photodetectors.
Structurea) D* [cm W−1 Hz1/2] Response time Stability Reference
PEDOT:PSS/MAPbI3−xClx/PCBM – 160 ns – [6]
Lead-based PEDOT:PSS/MAPbI3/PCBM/C60 >1012 1 µs – [7]
PTAA/MAPbBr3 SC/C60/BCP 1.5 × 1013 100 ns – [10]
PTAA/PEIE/CsPbIBr2/PCBM/BCP 9.7 × 1012 20 ns >83 d [11]
Au/Cs2AgInCl6 SC/Au 9.6 × 1011 ≈1.0 ms – [20]
Lead-free Au/(TMHD)BiBr5 SC/Au – 10.3 ms – [17]
Al/MASnI3/Au 8.8 × 1010 0.4 s – [19]
Au/Cs2AgInCl6/Au 5.7 × 1011 1.0 ms >14 d [21]
SnO2/Cs2AgBiBr6/Au 2.4 × 1010 ≈2.0 ms ≈180 d [22]
SnO2/Cs2AgBiBr6/TFB/Au 3.3 × 1012 17 ns >95 d This work
a)PEDOT:PSS: poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PCBM: [6,6]-phenyl C61 butyric acid methyl ester, PTAA: poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine, SC: single crystal, BCP: bathocuproine, TMHD: N,N,N,N-tetramethyl-1,6-hexanediammonium, PEIE: polyethylenimine ethoxylated, MA:CH3NH3.
Materials and Device Characterizations: The morphologies of Cs2AgBiBr6
film were characterized with SEM (LEO 1550). XRD patterns were measured with X-ray diffractometer (X’Pert PRO) with the wavelength of 1.5406 Å.
Ultraviolet–visible absorption spectra for different Cs2AgBiBr6 films were measured with Shimadzu spectrophotometer (UV-2450). The current density–voltage (J–V) curves were measured by recording the photocurrent and dark current with 2400 Series Source Meter (Keithley). The light used for J–V curves measurement was an air mass (AM) 1.5 Solar Simulator.
The effective area for every device cell was defined to be 7.25 mm2. The EQE curves were measured by a spectral response measurement system (QE-R3011, Enli Technology Co. Ltd) at zero bias voltage with the incident monochrome light calibrated by a standard Si photovoltaic cell. TRPL was used to characterize the electrodes charge carrier dynamics using 400 nm femtosecond excitation pulses (50 fs). The noise current was recorded by a lock-in amplifier (Stanford Research Systems SR830). Transient photocurrent was recorded by an oscilloscope with input resistances of 50 Ω. The incident pulse laser wavelength was chosen to be 337 nm with the pulse width of 4 ns. Thermal admittance spectra were used to determine the trap densities of the perovskite films based on the devices.
Sinusoidal voltages with amplitude of 30 mV from a function generator (Tektronix AFG 3000) were used to drive the devices; and the amplitudes and phases of the current signals were analyzed using the lock-in amplifier after preamplified by a low noise preamplifier (Stanford Research Systems SR570). With the measurement results, the capacitances can be calculated based on a parallel equivalent circuit model. The temperature of the devices was controlled using a closed cycle cryocooler (Advanced Research Systems DE202AE). The capacitance–voltage (C–V) curves were determined by measuring the capacitance when the applied DC bias voltage scanning from −0.5 to l.0 V. Based on the capacitance spectra measured at different temperature, the trap density (NT) distribution in energy (Eω) can be calculated with the following relations
d
T bid
N E V
qW C ωkTω
( )ω = − (4)
ln 2 0 2
E kT πνT
= ω
ω (5)
Figure 4. a) Thermal stability of the Cs2AgBiBr6 photodetector (black curve) and the MAPbI3 photodetector (red curve) under light illumination (450 nm) with the intensity of 10 µW cm−2. b)10 h of operation stability and c) long-term air stability for 2300 h of the Cs2AgBiBr6 photodetectors.
www.advancedsciencenews.com www.advopticalmat.de where Vbi is the built-in potential, W is the depletion width. Vbi and W
are derived from C–V measurement. C is the capacitance measured at angular frequency of ω and temperature of T, k is the Boltzmann constant, ν0 is a constant which can be obtained by fitting the relation of characteristic frequency with different T based on Equation (4).
Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.
Acknowledgements
J.Y., C.B., W.N. contributed equally to this work. This work was financially supported by the National Natural Science Foundation of China (51472164), the 1000 Talents Program for Young Scientists of China, Shenzhen Peacock Plan (KQTD2016053112042971), the Educational Commission of Guangdong Province (2015KGJHZ006 and 2016KCXTD006), the Science and Technology Planning Project of Guangdong Province (2016B050501005), a China Postdoctoral Science Foundation (2017M622744 and 2018T110886), the Swedish Research Council FORMAS (942-2015-1253), the European Commission Marie Skłodowska-Curie Actions (691210), and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009-00971).
Conflict of Interest
The authors declare no conflict of interest.
Keywords
Cs2AgBiBr6, environmental stability, fast response, lead-free perovskites, photodetectors, thermal stability
Received: December 12, 2018 Revised: April 10, 2019 Published online: May 3, 2019
[1] H. Melchior, M. B. Fisher, F. R. Arams, Proc. IEEE 1970, 58, 1466.
[2] E. R. Fossum, IEEE Trans. Electron Devices 1997, 44, 1689.
[3] M. Akiba, K. Tsujino, M. Sasaki, Opt. Lett. 2010, 35, 2621.
[4] S. D. Stranks, G. E. Eperon, G. Grancini, C. Menelaou, M. J. P. Alcocer, T. Leijtens, L. M. Herz, A. Petrozza, H. J. Snaith, Science 2013, 342, 341.
[5] D. Shi, V. Adinolfi, R. Comin, M. Yuan, E. Alarousu, A. Buin, Y. Chen, S. Hoogland, A. Rothenberger, K. Katsiev, Y. Losovyj, X. Zhang, P. A. Dowben, O. F. Mohammed, E. H. Sargent, O. M. Bakr, Science 2015, 347, 519.
[6] L. Dou, Y. (Micheal) Yang, J. You, Z. Hong, W.-H. Chang, G. Li, Y. Yang, Nat. Commun. 2014, 5, 5404.
[7] Q. Lin, A. Armin, D. M. Lyons, P. L. Burn, P. Meredith, Adv. Mater.
2015, 27, 2060.
[8] C. Bao, W. Zhu, J. Yang, F. Li, S. Gu, Y. Wang, T. Yu, J. Zhu, Y. Zhou, Z. Zou, ACS Appl. Mater. Interfaces 2016, 8, 23868.
[9] J. Yang, T. Yu, K. Zhu, Q. Xu, J. Phys. D: Appl. Phys. 2017, 50, 495102.
[10] C. Bao, Z. Chen, Y. Fang, H. Wei, Y. Deng, X. Xiao, L. Li, J. Huang, Adv. Mater. 2017, 29, 1703209.
[11] C. Bao, J. Yang, S. Bai, W. Xu, Z. Yan, Q. Xu, J. Liu, W. Zhang, F. Gao, Adv. Mater. 2018, 30, 1803422.
[12] H. Wang, D. H. Kim, Chem. Soc. Rev. 2017, 46, 5204.
[13] F. P. G. Arquer, A. Armin, P. Meredith, E. H. Sargent, Nat. Rev.
Mater. 2017, 2, 16100.
[14] D. Bryant, N. Aristidou, S. Pont, I. Sanchez-Molina, T. Chotchunang atchaval, S. Wheeler, J. R. Durrant, S. A. Haque, Energy Environ. Sci.
2016, 9, 1655.
[15] M. Lyu, J. H. Yun, P. Chen, M. Hao, L. Wang, Adv. Energy Mater.
2017, 7, 1602512.
[16] T. Leijtens, G. E. Eperon, N. K. Noel, S. N. Habisreutinger, A. Petrozza, H. J. Snaith, Adv. Energy Mater. 2015, 5, 1500963.
[17] C. Ji, P. Wang, Z. Wu, Z. Sun, L. Li, J. Zhang, W. Hu, M. Hong, J. Luo, Adv. Funct. Mater. 2018, 28, 1705467.
[18] X. W. Tong, W. Y. Kong, Y. Y. Wang, J. M. Zhu, L. B. Luo, Z. H. Wang, ACS Appl. Mater. Interfaces 2017, 9, 18977.
[19] A. Waleed, M. M. Tavakoli, L. Gu, Z. Wang, D. Zhang, A. Manikandan, Q. Zhang, R. Zhang, Y.-L. Chueh, Z. Fan, Nano Lett.
2017, 17, 523.
[20] J. Luo, S. Li, H. Wu, Y. Zhou, Y. Li, J. Liu, J. Li, K. Li, F. Yi, G. Niu, J. Tang, ACS Photonics 2018, 5, 398.
[21] L.-Z. Lei, Z.-F. Shi, Y. Li, Z.-Z. Ma, F. Zhang, T.-T. Xu, Y.-T. Tian, D. Wu, X.-J. Li, G.-T. Du, J. Mater. Chem. C 2018, 6, 7982.
[22] C. Chen, B. Du, W. Luo, Y. Liu, T. Li, D. Wang, X. Guo, H. Ting, Z. Fang, S. Wang, Z. Chen, Y. Chen, L. Xiao, Adv. Opt. Mater. 2018, 6, 1800811.
[23] G. Volonakis, A. A. Haghighirad, R. L. Milot, W. H. Sio, M. R. Filip, B. Wenger, M. B. Johnston, L. M. Herz, H. J. Snaith, F. Giustino, J. Phys. Chem. Lett. 2017, 8, 772.
[24] W. Ning, F. Wang, B. Wu, J. Lu, Z. Yan, X. Liu, Y. Tao, J. M. Liu, W. Huang, M. Fahlman, L. Hultman, T. C. Sum, F. Gao, Adv. Mater.
2018, 30, 1706246.
[25] W. Pan, H. Wu, J. Luo, Z. Deng, C. Ge, C. Chen, X. Jiang, W.-J. Yin, G. Niu, L. Zhu, L. Yin, Y. Zhou, Q. Xie, X. Ke, M. Sui, J. Tang, Nat.
Photonics 2017, 11, 726.
[26] C. Bi, Q. Wang, Y. Shao, Y. Yuan, Z. Xiao, J. Huang, Nat. Commun.
2015, 6, 7747.
[27] H. Do Kim, H. Ohkita, H. Benten, S. Ito, Adv. Mater. 2016, 28, 917.
[28] W. Gao, C. Ran, J. Xi, B. Jiao, W. Zhang, M. Wu, X. Hou, Z. Wu, ChemPhysChem 2018, 19, 1696.
[29] E. Greul, M. L. Petrus, A. Binek, P. Docampo, T. Bein, J. Mater.
Chem. A 2017, 5, 19972.
[30] C. Wu, Q. Zhang, Y. Liu, W. Luo, X. Guo, Z. Huang, H. Ting, W. Sun, X. Zhong, S. Wei, S. Wang, Z. Chen, L. Xiao, Adv. Sci. 2018, 5, 1700759.
[31] M. L. M. Wang, P. Zeng, S. Bai, J. Gu, F. Li, Z. Yang, Sol. RRL 2018, 2, 1800217.
[32] H. Ko, D. H. Sin, M. Kim, K. Cho, Chem. Mater. 2017, 29, 1165.
[33] Y. Lou, M. Fang, J. Chen, Y. Zhao, Chem. Commun. 2018, 54, 3779.
[34] H. Duan, H. Zhou, Q. Chen, P. Sun, S. Luo, T. Song, B. Bob, Y. Yang, Phys. Chem. Chem. Phys. 2014, 17, 112.
[35] M. Samiee, S. Konduri, B. Ganapathy, R. Kottokkaran, H. A. Abbas, A. Kitahara, M. Samiee, S. Konduri, B. Ganapathy, R. Kottokkaran, Appl. Phys. Lett. 2014, 105, 153502.
[36] Z. Zhu, Y. Bai, H. K. H. Lee, C. Mu, T. Zhang, L. Zhang, J. Wang, H. Yan, S. K. So, S. Yang, Adv. Funct. Mater. 2014, 24, 7357.
[37] G. J. A. H. Wetzelaer, M. Scheepers, A. M. Sempere, C. Momblona, J. Ávila, H. J. Bolink, Adv. Mater. 2015, 27, 1837.
[38] B. Conings, J. Drijkoningen, N. Gauquelin, A. Babayigit, J. D’Haen, L. D’Olieslaeger, A. Ethirajan, J. Verbeeck, J. Manca, E. Mosconi, F. De Angelis, H. G. Boyen, Adv. Energy Mater. 2015, 5, 1500477.
[39] S. Bai, Z. Wu, X. Wu, Y. Jin, N. Zhao, Z. Chen, Q. Mei, X. Wang, Z. Ye, T. Song, R. Liu, S.-t. Lee, B. Sun, Nano Res. 2014, 7, 1749.
