Self-powered CsPbBr3 nanowire photodetector with a vertical structure

Author’s Accepted Manuscript Self-Powered CsPbBr3 Nanowire Photodetector with a Vertical Structure Hai Zhou, Zhaoning Song, Corey R. Grice, Cong Chen, Jun Zhang, Yifan Zhu, Ronghuan Liu, Hao Wang, Yanfa Yan www.elsevier.com/locate/nanoenergy

PII: DOI: Reference:

S2211-2855(18)30684-0 https://doi.org/10.1016/j.nanoen.2018.09.040 NANOEN3045

To appear in: Nano Energy Cite this article as: Hai Zhou, Zhaoning Song, Corey R. Grice, Cong Chen, Jun Zhang, Yifan Zhu, Ronghuan Liu, Hao Wang and Yanfa Yan, Self-Powered CsPbBr3 Nanowire Photodetector with a Vertical Structure, Nano Energy, https://doi.org/10.1016/j.nanoen.2018.09.040 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Self-Powered CsPbBr3 Nanowire Photodetector with a Vertical Structure Hai Zhou,a,b Zhaoning Song,b Corey R. Grice,b Cong Chen,b Jun Zhang,a Yifan Zhu,a Ronghuan Liu,a Hao Wanga, *and Yanfa Yanb, * a

Hubei Key Laboratory of Ferro & Piezoelectric Materials and Devices, Faculty of Physics &

Electronic Science, Hubei University, Wuhan, 430062, P.R. China. b

Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and

Commercialization, The University of Toledo, Toledo, Ohio, 43606, USA.

Prof. Hao Wang: [email protected] Prof. Yanfa Yan: [email protected] *

Corresponding Author

ABSTRACT Single crystal halide perovskite nanowires (NWs) have attracted much attention in high-performance photodetectors (PDs) due to their high photoluminescence quantum yields, large carrier mobilities, and long carrier diffusion lengths. So far, most high-performance NW PDs are fabricated based on individual or aligned NWs which require complicated preparation process. Furthermore, it is challenging for these NW PDs to poessess self-powered feature. Here, we report self-powered perovskite NW PDs with a vertical p-i-n structure in which CsPbBr3 NWs are grown by a combination of solution-phase process and halide exchange. Before depositing hole selective layer, poly(methyl methacrylate) is coated on perovskite NW film to fill the voids, which passivates surfaces of perovskite NWs and reduces the dark current.

Our optimized CsPbBr3 NW PDs show dark current density as low as 4.0 nA cm-2

and photocurrent density as high as 22.9 mA cm-2 under a 473 nm laser illumination with the 1

light intensity of 641 mW cm-2, leading to a high linear dynamic range of 135 dB.

In

addition, our perovskite NW PDs display highly self-powered performance with ultrohigh on/off ratios of above 106, responsivity of up to 0.3 A W-1 and detectivity of up to 1×1013 Jones at 0 V. Graphical Abstract:

Self-powered perovskite NW PDs with a vertical p-i-n structure in which CsPbBr3 NWs are grown by a combination of solution-phase process and halide exchange. Our optimized CsPbBr3 NW PDs show dark current density as low as 4.0 nA cm-2 and photocurrent density as high as 22.9 mA cm-2, leading to a high linear dynamic range of 135 dB.

In addition, the

perovskite NW PDs display highly self-powered performance with ultrohigh on/off ratios of above 106, responsivity of up to 0.3 A W-1 and detectivity of up to 1×1013 Jones at 0 V

KEYWORDS: self-powered, nanowire, perovskite, photodetector, CsPbBr3 As a promising class of materials, lead halide perovskites showed attractive applications in solar cells,1, 2 photodetectors (PDs)3-5 and light emitting diodes6, 7 due to their high absorption coefficients, relatively large carrier mobilities, and good defect tolerance.8,

9

It was well

known that the carrier mobility of the perovskites affects the charge extraction properties and recombination dynamics, determining the device performance.10 However, the perovskite 2

polycrystalline (PC) films suffer from the low carrier mobility (< 10 cm2 V-1 s-1) and undesired charge recombination at the grain boundaries,11, relatively poor device performance.

12

and, therefore, resulting in

Compared with PC perovskite films, single-crystalline

perovskite nanowires (NWs) with well defined structures possess higher photoluminescence (PL) quantum yields, larger carrier mobilities, and longer carrier diffusion lengths.13-15 In addition, more direct charge transport pathway can be provided by the one-dimensional perovskite NWs, benefiting the efficient collection of carriers by the electrodes. The merits of perovskite NWs indicate that PDs using such perovskite NWs should lead to high performances. Deng and co-authors16 reported metal-semiconductor-metal (MSM) PDs based on NW network with a responsivity (R) of 0.1 A W-1, a switching ratio of 300 and a response time of about 0.3 ms. This relatively low performance may be due to the structurally heterogeneous perovskite network consisting of mixed NWs and belt-type crystals. Many approaches have focused on the preparation of aligned NWs for application in MSM PDs with ultra-high performance.17-20 Spina and co-authors17 reported on the graphoepitaxial liquid-solid growth of aligned NWs of the photovoltaic compound CH3NH3PbI3 in open nanofluidic channels and fabricated NW PDs with response times of 2 - 5 seconds and Rs as high as 6 × 106 A W-1. Deng and co-authors18 reported a fluid-guided antisolvent vapor-assisted crystallization (FGAVC) method for large-scale fabrication of aligned single-crystalline MAPb(I1-xBrx)3 NW arrays, and the PDs made from the NW arrays exhibited high performance with a R of 12500 A W−1 and a linear dynamic rang (LDR) of 115 dB.

In addition, single perovskite nanorod based PD is another approach to reach high

performance. Yang and co-authors21 reported PDs based on a single CsPbI3 nanorod with a R of 2.92 × 103 A W-1, a response time of 0.05 ms, and a detectivity (D*) of up to 5.17 × 1013 Jones.

Gui and co-authors22 reported a high-performance single CsPbBr3 perovskite

microwire PD showing a R of up to 118 A/W and a D* of >1012 Jones.

However, these

approaches for high-performance perovskite NW PDs need complicated preparation processes 3

and have poor reproducibility. Also the photocurrents of the PDs based on aligned NWs or single NW with MSM structure are very low due to the limited light absorption cross section or the large channel length between the metal electrodes. Moreover, these approaches face challenges for producing high performance self-powered PDs because for achieving the self-powered feature, p-n junction or a Schottky barrier junction are required, but these are great obstacles for the individual or aligned perovskite NW PDs due to the difficulties of the p or n-doping in perovskites23 and the complicated nanoscale manipulation.17-22 Thus, a p-i-n vertical structure with perovskite NW networks sandwiched between the electron selective layer (ESL) and hole selective layer (HSL) will be a good alternative, and it can function both the merits of perovskite NWs and the p-i-n vertical junction, which is used in most of self-powered PDs.3-5 Here, we report self-powered perovskite NW PDs with a vertical p-i-n structure in which CsPbBr3 NWs was grown by a combination of solution-phase process and halide exchange (SPP-HE), which was reported in our previous work.24 The PDs use

plasma-enhanced

atomic-layer

deposited

(PEALD)

SnO2

and

spin-coated

Poly(triarylamine) (PTAA) as the ESL and HSL, respectively. For achieving a high quality p-i-n device, poly(methyl methacrylate) (PMMA ) is coated on perovskite NWs to fill the voids before the deposition of PTAA layer. The PMMA passivates surface defects of perovskite NWs and greatly reduces the dark current density (Jdark). After filled by PMMA, our CsPbBr3 NW PDs not only show an ultra-low Jdark of 4.0 nA cm-2, but also achieve a high photocurrent density of 22.9 mA cm-2 under a 473 nm laser illumination with the light intensity of 641 mW cm-2. In addition, our CsPbBr3 NW PDs show highly self-powered performance with R, D*, on/off ratio, and LDR of up to 0.3 A W-1, 1.0×1013 Jones, above 106, and 135 dB, respectively. To the best of our knowledge, this is the first report on self-powered CsPbBr3 NW PDs with a vertical structure to date.

Results and Discussion 4

Figure 1 Schematic illustration of the synthesis process of the CsPbBr3 NWs and CsPbBr3 micro- and nanostructures.

Figure 1 shows the schematic illustration of the synthesis process of the CsPbBr3 NWs via the SPP-HE method.

First, PbI2 coated substrates were soaked in a methanol solution

containing 8 mg/ml CsI for 15 h to fabricate non-perovskite-phase CsPbI3 (N-CsPbI3) NWs (vide infra).

After that, the N-CsPbI3 NW films were soaked in a methanol solution

containing 8 mg/ml CsBr for 4 h to obtain the N-CsPbBr3 NW films via a halide exchanging process. The resulting N-CsPbBr3 NWs were annealed at 200 oC for 30 min to form the orthorhombic CsPbBr3 NWs. Through this process, the CsPbBr3 NW films consisted of the pure NWs without other nano- or micro-structures have been obtained (Figure S1b). In contrast, when CsPbBr3 is prepared by reacting PbI2 films and CsBr solution directly, the resulting films are comprised of various nano- or micro-structures(Figure S1a).

In our

process, at the first step when the PbI2 films were soaked in a CsI solution, the N-CsPbI3 NW films formed a non-perovskite phase with an exciton absorption peak located at ~420 nm (Figure S2a), which is consistent with our previous work.24

When the N-CsPbI3 NW film

was soaked in CsBr solution for 4 h, the color of the film turned white completely, indicating that the N-CsPbI3 NW film was transferred to the N-CsPbBr3 NW film through the Br+ 5

exchange, whose absorption edge was shifted to 390 nm (Figure S2b).

Finally, the

perovskite-phase CsPbBr3 NW film with the absorption edge of 542 nm (Figure S3c) was obtained by annealing the N-CsPbBr3 NW film at 200 oC for 30 min.

Figure 2 (a) Top-view SEM image of a CsPbBr3 NW film. (b) XRD pattern of the CsPbBr3 NW film. (c) TEM image and (d-f) corresponding EDS elemental mappings of a individual CsPbBr3 NW.

Figure 2a shows the top view scanning electron microscopy (SEM) image of a CsPbBr3 NW thin film, showing well controlled growth of NWs by the SPP-HE method.

Figure 2b

displays the X-ray diffraction (XRD) pattern of the CsPbBr3 NW thin film, which well matches with the orthorhombic perovskite crystal structure with strong (100), (111), and (200) diffraction peaks, consistent with the prevarious reports.22, 6

24

Additionally, a individual

CsPbBr3 NW with a diameter of about 180 nm was characterized by transmission electron microscopy (TEM), shown in Figure 2c. Figure 2d-f displays the homogeneous distributions of Cs, Pb, and Br elements in the individual NW. It is worthy to note that no I signal was observed, indicating the halide exchange was complete through the process.

Figure 3 (a) Schematic illustration of the perovskite NW PD. (b) Energy band diagram of the perovskite NW PD. (c) Cross-sectional SEM image of the perovskite NW PD. The scale bar is 500 nm. (d) Dark I-V curves of the perovskite NW PDs coated with PMMA at various rpm. (e) On/off ratio curves. (f) Jsc of the perovskite NW PDs coated with PMMA at various rpm. The optical power is about 641 mW cm-2.

The ultra-high crystal quality and optical characteristics of perovskite NWs encourage us to fabricate NW-based PDs. Figure 3a shows the structure of our perovskite NW PDs (glass/ITO/PEALD-SnO2/perovskite MCs/PTAA/Au) with its band diagram shown in Figure 3b.

Figure 3c shows distinct layers of SnO2/ITO, PMMA+perovskite NWs, and Au/PTAA,

and the thickness of active layer is about 800 nm. 7

For high performance PDs, the dark current must be low. A high dark current not only limits the dynamic range of the PD but also enlarges noise levels, and thus, reducing the signal-to-noise ratio.

The use of PMMA to passivate NW surface plays an important role in

obtaining low Jdark, due to a combination of surface passivation of perovskite NWs and the blocking the leakage paths between the ETL and HTL. Without PMMA, the Jdark‘s of our PDs are at the mA cm-2 level at -0.1 V (Figure 3d), which are very high and infeasible for the high-performance PDs.

With PMMA passivation of NW surface and filling the voids, the

Jdark is significantly reduced. We find that the spin speed for PMMA coating affects the Jdark. When the spin speed decreases from 5000 to 3000 rpm, the Jdark is reduced by more than two orders of magnitude. The Jdark does not significantly drop when the spin speed further reduced to 1000 rpm. Thus, we used a spin speed of 3000 rpm for PD optimization. We anticipate that the spin speed controls the amount of PMMA filling the perovskite NW films. While too little PMMA cannot fully coat the perovskite NW surface and completely fill the voids that is needed for blocking the direct contact between the ETL and HTL, too much PMMA can inhibit the hole transport from NWs to PTAA and Au. To examine the effects of PMMA passivation on PD performance, a 473 nm laser with optical power of 641 mW cm-2 was applied as the light source to CsPbBr3 NW PDs with and without PMMA, and the current density-voltage (J-V) curves are shown in Figure S3.

Under

illumination of the laser, all samples show good photoelectric characteristic with their on/off ratio curves shown in Figure 3e. With the decrease of the applied reverse bias, all samples show an increase in on/off ratio, which is caused by the reduced dark current as decreasing the applied reverse bias. Obviously, the sample filled with the PMMA at 3000 rpm shows the highest on/off ratio at any given bias, and its maximum value of on/off ratio exceeds 106 at 0 V, which is larger than that of perovskite NW PDs reported in literature.16-22, 24 From Figure 3f, our perovskite NW PDs show an excellently self-powered performance with the highest Jsc

8

reaching 22.9 mA cm-2 at the optical power of 641 mW cm-2 for the device prepared with spin-coated PMMA at 3000 rpm.

Figure 4 (a) J-T curve in semi-logarithmic coordinates at the light intensity of 641 mW cm-2. (b) J-T curve at the light intensity of 6.4×10-4 mW cm-2. (c) J-T curve with long time test in air.

(d) 3 dB bandwidth of the PD. (e) Time response of the PD.

(f) Time-resolved PL

spectra of the CsPbBr3 NWs grown on glass substrates with various PMMA coatings.

All

curves (a-e) are measured at 0V.

We further evaluate the performance of our best perovskite NW PDs (filled by 3000-rpm PMMA) under a strong (641 mW cm-2) and weak (6.4×10-4 mW cm-2) light illumination, as shown in Figure 4a and 4b, respectively.

Through turning on and off the laser repeatedly,

the PD shows good photoresponse characteristics both for the strong and weak light. Clearly, under the strong light the PD shows a significantly high photocurrent density of 22.9 mA cm-2. Under the weak light, the PD also shows a good response due to the low Jdark of 4.0 nA cm-2. Moreover, our PDs show a good stable and repeatable characteristic when the device is under 9

illumination for about 30 min in air (Figure 4c), and no degradation has been observed.

The

3 dB bandwidth of 1000 Hz is measured by a rotary optical chopper, the frequency of which can be modulated from 1 to 4500 Hz, and the results are shown in Figure S4 and 4d. Figure 4e shows the normalized current vs time curve of the self-powered PD, from which the rise (trise, 0.4 ms) and fall (tfall, 0.43 ms) times are calculated. To investigate the effects of PMMA passivation on the surface defect of perovskite NWs, time-resolved photoluminescence (TRPL) measurements were carried out. The TRPL curves of the perovskite NW films coated with PMMA at various spin speeds are shown in the Figure 4f.

The PL decay traces were fitted by using a bi-exponential decay function to

determine the decay times of the fast and slow components, which are summarized in Table S1. The PL lifetimes of a few ns are consistent with values of CsPbBr3-based nanostructures reported in the literature.25-27 Looking into the details of PL decay parameters, the fast component (τ1) in the PL decay indicates the presence of trap states, especially at the surfaces, and the slow component (τ2) is attributed to the free carrier recombination. For the perovskite NWs coated with PMMA, the value of τ1 increased from 0.19 to 0.90 ns, indicating that the PMMA effectively passivated the surface defects of the perovskite NWs. When the rpm decreased from 5000 to 1000, the value of τ1 also increased obviously, suggesting that more PMMA passivate more surface defects.

In addition, our perovskite NW PDs show a

relatively long Voc decay time28 (Figure S5). From the Voc decay and the AC impedance measurements (in dark) shown in Figure S6, the carrier lifetime () of the real device can be estimated with the value of above 0.3 ms.

The long carrier lifetime should be

attributed to the combination of surface passivation of perovskite NWs and the PMMA blocking of leakage pathways.

10

Figure 5 (a) Linear dynamic rang of the PD. (b) Responsivity and detectivity of the device under various optical power.

As a figure-of-merit of PDs, the LDR is very useful for characterizing the photocurrent range and can be given by the formula LDR  20log( J ph / J dark )

(1)

where Jph and Jdark are the photo- and dark-current density, respectively.

For these values of

Jsc treated by linearly fitting, the R-Squared (coefficient of determination) can be calculated to be 0.99968 (Figure 5a), indicating the perfect linearity of the data.

In addition, a LDR of 114

is achieved when using the smallest light current as a denominator of the formula.

When

using the Jdark of 4 nA cm-2, the LDR of our device can reach 135, which is very large in comparison with other perovskite-based PDs (Table S2).21-22, 24 From Figure 5b we can see the values of the spectral R and D* are almost constant with the optical power ranging from 102 to 10-4 mW cm-2, further confirming the measured large LDR of the NW PDs. From the curves, the PDs show all of the R and D* values are about 0.3 A W-1 and 1.0×1013 Jones (1 Jones = 1 cm Hz1/2 W-1), respectively.

These high D*

values are beneficial for the big LDR of the PD, in which the low Jdark and large Jsc determine the upper limitation. The deviation of the photocurrent from the linearity in the optical power region may be induced by the ratio of carrier lifetime and the carrier extracted time.29 From above, the value of  reaches 0.3 ms, which is much larger than that of the carrier extracted 11

time (~ 100 ns).30 Thus our PDs can maintain a good linear even when the optical power is up to 102 mW cm-2. In summary, we have reported high performance self-powered perovskite PDs with a vertical structure. Using PMMA to fill the voids and passivate perovskite NWs is a key to achieved the high performance.

Our optimized CsPbBr3 NW PDs showed the lowest Jdark of

4.0 nA cm-2 and the highest Jph of up to 22.9 mA cm-2 at zero bias, achieving a big LDR of 135 dB.

In addition, our perovskite NW PDs display highly self-powered performance with

ultrahigh on/off ratio, responsivity and detectivity at 0 V.

Experimental Sections SnO2 film preparation: The patterned ITO glass substrates were washed by standard cleaning process for 30 min and then the 15-nm SnO2 film was prepared onto the patterned ITO substrate by PEALD (Ensure Scientific Group Auto ALD-PE V2.0). CsPbBr3 NW synthesis: The CsPbBr3 NWs were synthesized by the SPP-HE method. First, PbI2 (1 mol/L in N,N-Dimethylformamide) was spin-coated on SnO2 coated ITO substrates at 4000 rpm for 60 s and annealed at 100 oC for 10 min. Then the samples were soaked in CsI solution (8 mg/ml in methanol) for 15 h to fabricate N-CsPbI3 NWs. To obtain N-CsPbBr3 NWs, the N-CsPbI3 NW film was soaked in CsBr solution (8 mg/ml in methanol) for 4 h, which was the halide exchanging process. After that, the N-CsPbBr3 NWs was annealed at 200 oC for 30 min, and the orthorhombic CsPbBr3 NWs had been prepared. Device fabrication: For fabricating high performance PDs, the PMMA was spin-coated on CsPbBr3 NW film at various speeds for 60 s to passivate the surface of the CsPbBr3 NWs and fill the voids among the NWs. After that, the PTAA (~20 nm) was spin-coated and then 60-nm Au top electrode was thermally evaporated with a patterned mask.

Finnaly, the active

area of each device was about 0.12 cm2, which is defined by the overlap between Au and ITO.

12

Characterization: High-resolution SEM characterization, XRD patterns and absorption spectra of the CsPbBr3 NWs were taken by a field emission SEM (Hitachi S-4800), RigakuUltima III with Cu K radiation under operation conditions of 40 kV and 44 mA excitation and UV-Vis spectrophotometer (PerkinElmer Lambda 1050), respectively.

The

TRPL measurement is taken by a modular fluorescence liftetime system (DeltaflexTM ). AC impedance measurements were conducted by a Solarton Modulab potentiostat/galvanostat. The J-V and J-T curves were measured by a Keithley 2401 sourcemeter.

The fast response

characteristic and TPD measurements were measured by an oscilloscope.

The optical source

was a laser (100 mW) with the light intensity changed by neutral density optical filters and calibrated by a standard Si diode.

ASSOCIATED CONTENT The Supplementary Information provides information about the experimental illustration, characterization of NWs and the device performance.

ACKNOWLEDGMENT This work at Hubei University is supported by the National Natural Science Foundation of China (No. 11874143), and the work is also financially supported by the Office of Naval Research under Contract no. N00014-17-1-2223, Air Force Research Laboratory under Space Vehicles Directorate (FA9453-11-C-0253), National Science Foundation under contract no. CHE-1230246, DMR−1534686, and ECCS1665028, and the Ohio Research Scholar Program. We thank Pengbin Gui and Prof. Guojia Fang at Wuhan University for TRPL measurements.

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Hai Zhou is an Associate Professor of Faculty of Physics and Electronic Science, Hubei University, Wuhan, China. He received the M.S. and Ph.D. degree in Microelectronics and Solid State Electronics from Wuhan University, Wuhan, China. July 1, 2017, Hai joins Prof. Yanfa Yan’s group as a visiting scholar. His main research areas include self-power photodetectors, ultraviolet LEDs devices, and photoelectric devices based on perovskite materials. Zhaoning Song received his BS degree in physics from Xiamen University, China, in 2009 and his PhD in physics from the University of Toledo (UT) under the guidance of Prof. Michael Heben. He is currently a research assistant professor in Prof. Yanfa Yan’s group at UT’s Wright Center for Photovoltaic Innovation and Commercialization. His research interests include solution processing of thin-film photovoltaics and nanomaterials for optoelectronic applications. Corey Grice earned Bachelor of Science in Engineering degrees in Chemical Engineering and Materials Science & Engineering from the University of Michigan – Ann Arbor in 2005. He entered graduate school at the University of Toledo in 2011 and completed a Professional Science Masters degree in Physics with specialization in Photovoltaics in 2013. He is currently pursuing a PhD in Physics under the guidance of Dr. Yanfa Yan, with research focusing on development and characterization of various novel and/or low cost thin film photovoltaic and photoelectrochemical materials and optoelectronic devices.

Cong Chen was educated at Wuhan University where he received a bachelor's degree in 2016. Now he is a Ph.D. guided by Prof. Guojia Fang in School of Physics and Technology at Wuhan University. His research interest mainly focuses on perovskite solar cells.

Prof. Jun Zhang received her BS degree in electronic materials and devices from Hubei University in 2000 and M.Sc. degree in condensed matter physics from Institute of Solid State Physics, CAS in 2003. Under the support of Oversea Research Scholarship, she undertook her PhD in nanomaterials and nanostructures at Salford University, UK. In 2007, she joined Faculty of Physics and Electronic Technology, Hubei University. Now, her research is mainly focused on metal halide perovskite solar cells and photodetectors, dye sensitized solar cells, as well as nanomaterials and nanodevices based on metal oxide semiconductors. Yifan Zhu is now being a university student of Prof. Hai Zhou at Hubei University. Most recently his research interest focuses on organic-inorganic perovskite photodetectors.

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Ronghuan Liu has received his B.E. degree in Hubei University of China in 2016. He is currently a M.S. candidate at Hubei University, under the supervision of Prof. Hai Zhou. His current research direction is perovskite photodetector.

Hao Wang is Chair Professor of the Faculty of Physics and Electronic Science and Dean of Graduate School of Hubei University. He received his Ph. D from Huazhong University of Science and Technology in 1994 and worked as a postdoc at Peking University and the Chinese University of Hong Kong till 2002. He has published over 150 refereed journal papers (such as Adv. Energy Mater., ACS Nano, Nano Energy), held 14 patents, and authored 2 books. His current research interests involve energy and information applications of nanostructured materials including solar cells, fuel cells, non-volatile memory and optoelectronic devices, and magnetic nanostructures.

Yanfa Yan is a Professor and the Ohio Research Scholar Endowed Chair in the Department of Physics and Astronomy at the University of Toledo (UT). He earned MS and Ph D in Physics from Wuhan University. Previously, he was a Principal Scientist at the National Renewable Energy Laboratory (NREL), USA. His research interest includes theory of defect physics and electronic properties in semiconductors, materials synthesis, and thin film solar cell fabrication. He has received DOE/EERE Young Investigator and R&D 100 awards. He is a Fellow of the American Physical Society.

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Highlights 1. Self-powered perovskite NW PDs with a vertical p-i-n structure in which CsPbBr3 NWs are grown by a combination of solution-phase process and halide exchange are first reported. 2. Poly(methyl methacrylate) is introduced to fill the voids among perovskite NWs, which passivates surfaces of perovskite NWs and reduces the dark current. 3. Our optimized CsPbBr3 NW PDs show dark current density as low as 4.0 nA cm-2 and photocurrent density as high as 22.9 mA cm-2, leading to a high linear dynamic range of 135 dB. 4. Highly self-powered performance is achieved with ultrohigh on/off ratios of above 106, responsivity of up to 0.3 A W-1 and detectivity of up to 1×1013 Jones at 0 V.

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