Nanodots Decorated CdS Nanoribbons for High-Performance

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MoO3 Nanodots Decorated CdS Nanoribbons for High-performance, Homojunction Photovoltaic Devices on Flexible Substrates Zhibin Shao, Jiansheng Jie, Zheng Sun, feifei xia, Yuming Wang, Xiao-Hong Zhang, Ke Ding, and Shuit-Tong Lee Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.5b01087 • Publication Date (Web): 13 Apr 2015 Downloaded from http://pubs.acs.org on April 15, 2015

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MoO3 Nanodots Decorated CdS Nanoribbons for High-performance, Homojunction Photovoltaic Devices on Flexible Substrates Zhibin Shao, Jiansheng Jie,* Zheng Sun, Feifei Xia, Yuming Wang, Xiaohong Zhang,* Ke Ding, and Shuit-Tong Lee * Institute of Functional Nano & Soft Materials (FUNSOM), Collaborative Innovation Center of Suzhou Nano Science and Technology, Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, P. R. China

Abstract: P-n homojunctions are essential components for high-efficiency optoelectronic devices. However, the lack of p-type doping in CdS nanostructures hampers the fabrication of efficient photovoltaic devices from homojunctions. Here we report a facile solution-processed method to achieve efficient p-type doping in CdS nanoribbons (NRs) via a surface charge transfer mechanism by using spin-coated MoO3 nanodots (NDs). The NDs-decorated CdS NRs exhibited a hole concentration as high as 8.5×1019 cm-3, with the p-type conductivity tuneable in a wide range of seven orders of magnitude. The surface charge transfer mechanism was characterized in detail by x-ray photoelectron spectroscopy, Kelvin probe force microscopy, and first-principle calculation. CdS NR-homojunction photovoltaic (PV) devices fabricated on a

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flexible substrate exhibited a power conversion efficiency of 5.48%, which was significantly better than most of the CdS nanostructure-based heterojunction devices, presumably due to minimal junction defects. Devices made by connecting cells in series or in parallel exhibited enhanced power output, demonstrating the promising potential of the homojunction PV devices for device integration. Given the high efficiency of the surface charge transfer doping and the solution-processing capability of the method, our work opens up unique opportunities for highperformance, low-cost optoelectronic devices based on CdS homojunctions.

Keywords: MoO3 nanodots, CdS nanoribbons, homojunction, flexible, photovoltaic devices

Introduction P-n homojunctions, which are made of the same semiconductor with opposite conduction types, play an important role in high-performance optoelectronic devices such as light-emitting diodes (LEDs), laser diodes (LDs), and photovoltaic (PV) devices.1,2 In comparison with p-n heterojunctions, which are composed of semiconductors with different components or structures, p-n homojunctions possess superior optoelectronic properties owing to perfect band alignment, negligible lattice mismatching, and minimum junction defects.3 However, it is well known that most of the II-VI group semiconductors exhibit strong unipolar characteristic, i.e. either only nor p-type doped, because complementary doping is hampered by strong self-compensation effect,4 low solubility of dopants,5 and deep acceptor levels.6 As a result, it remains a challenge to construct high-quality p-n homojunctions based on II-VI group semiconductors. As a typical wide direct band-gap II-VI semiconductor, cadmium sulfide (CdS) nanostructures have attracted much attention in recent years, because of their extraordinary


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optoelectronic properties.7,8 Applications of CdS nanostructures in diverse fields such as fieldeffect transistors (FETs),9-11 integrated circuits,12 LEDs,13,14 photodetectors,8,15,16 and solar cells 17-27

have been intensively investigated. The size-tunable bandgap and strong absorption of CdS

nanostructures in the visible light range render them desirable candidates for high-performance PV devices.28 Nevertheless, the intrinsic CdS nanostructures show solely n-type conductivity due to the existence of sulfur vacancies, and doping in CdS nanostructures always results in n-type conductivity due to strong self-compensation effect.9,29,30 The lack of efficient p-type doping for CdS hinders the development of high-performance PV devices from CdS homojunctions.29 To bypass the difficulty of p-type doping, CdS nanostructure-based PV devices were normally fabricated in other forms, such as heterojunctions (CdS as n-type semiconductor material),18-21 Schottky junctions (high work-function metals used as Schottky contacts with n-type CdS),23,24 and organic-inorganic hybrid structures (CdS as electron transport layer).25,26 For the heterojunction devices, the efficiency of charge collection is restricted by the polycrystalline structures, high densities of interface states, and grain boundaries within the junction zones.22 The complex fabrication process also leads to high cost and inferior reproducibility of the heterojunction devices. Meanwhile, though the Schottky junction and organic-inorganic hybrid devices are easier to fabricate, a desirable efficiency has not been achieved yet. Recently, Yang and co-workers reported the fabrication of CdS-Cu2S core-shell p-n heterojunction nanowires (NWs) through cation exchange reaction.22 The NW heterojunction devices showed a promising power conversion efficiency (PCE) of ~5.4%, but sophisticated control of the Cu2S shell was required to achieve the high performance. Owing to the high surface-to-volume ratio, surface plays a key role in the optical,31 mechanical,32 catalytic,33 and optoelectronic properties16 of semiconductor nanostructures. For


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instance, the electrical transport properties of Si NWs were dominantly related to the surface states, so that transition of conduction types was observed upon adsorption of surface water molecule or change in PH value.34,35 Studies also revealed that modifying the surface of carbon nanotubes (CNTs) with organic molecules or alkali metals could readily tune the conduction types, leading to the fabrication of CNT homojunctions.36,37 The charge transfer between surface states and semiconductor nanostructures is suggested to be responsible for this phenomenon. In comparison with conventional doping method, which takes effect by introducing impurity elements into the host lattice of semiconductors, surface charge transfer doping is not restricted by self-compensation effect or dopant solubility, and can retain the high performance of nanostructures by reducing carrier scattering in the bulk. However, gas molecules and alkali metals were mostly involved in the surface charge transfer doping in previous reports, rendering the doping processes complex and unstable, which will inevitably hinder applications in practical devices. Herein, we report an efficient and simple solution process to produce p-type conductivity in CdS nanostructures via surface charge transfer doping by using MoO3 nanodots (NDs). Remarkably, even discrete decoration of MoO3 NDs on CdS nanoribbon (NR) surface was capable of achieving degenerate doping of the NR, yielding a hole concentration as high as 8.5×1019 cm-3. Both experimental and theoretical investigations confirmed the intense charge transfer between CdS NRs and MoO3 NDs. Furthermore, flexible PV devices based on CdS NR p-n homojunctions were constructed by selectively decorating one-half parts of the NRs with MoO3 NDs. The resulting homojunction device exhibited outstanding photovoltaic performance, and remained robust against bending stress. In particular, the flexible homojunction devices showed high efficiencies of 5.48%, which are comparable to the best values reported for CdS


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nanostructures-based heterojunction devices, yet they were fabricated by a simple process and exhibited high flexibility (Table S1, Supporting Information).20-22 Our work paves the way towards high-efficiency flexible nano-optoelectronic devices based on CdS homojunctions.

Results and Discussion Figure 1a illustrates the decoration process of MoO3 NDs on CdS NRs via spin coating. The single-crystalline CdS NRs have a wurtzite structure with a thickness of 70-130 nm, width of 0.7-6 µm, and length up to 400 µm (Figure S1 and S2, Supporting Information). MoO3 NDs with sizes of ca. 3 nm were spontaneously formed and deposited on the surface of CdS NRs during evaporation of the MoO3 aqueous solution (Figure S3, Supporting Information).38 Figure 1b shows the low-magnification transmission electron microscope (TEM) image and the corresponding EDS spectrum of the MoO3 NDs-decorated CdS NR. No trace of MoO3 NDs can be found in both the TEM image and the EDS spectrum, due to the low coverage of NDs on NR surface. High-resolution TEM (HRTEM) characterization, Figure 1c, unveils that the MoO3 NDs are discretely distributed on the NR surface. The fringes with a lattice spacing of 0.23 nm correspond to the (600) lattice plane of MoO3 (JCPDS file no. 65-2421). Figure 1d shows the scanning transmission electron microscopy (STEM) image of the NDs-decorated NR by spincoating 0.1 wt% MoO3 solution, revealing the existence of some protuberances at the NR edge. Though the Mo signal is too weak to be identified from noise in EDS mapping of Mo, EDS mapping of Cd shows a smooth NR edge (Figure 1e), suggesting the protuberances very likely come from the MoO3 NDs on NR surface. The surface coverage of NDs on NR surface was estimated to be ~19% based on HRTEM and STEM investigations. In a control experiment, the MoO3 aqueous solution was directly drop-casted onto the CdS NR to form a thick MoO3 NDs


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layer on the NR (Figure S4, Supporting Information). In this case, the 4 nm thick MoO3 NDs shell could be clearly identified from the TEM image as well as the EDS mapping. To evaluate the charge transfer effect between CdS NRs and MoO3 NDs, bottom-gate FETs based on the NDs-decorated NRs were constructed on a SiO2 (300 nm)/n+-Si substrate (Figure 2a). Cu (4 nm)/Au (50 nm) bilayer electrodes, which form ohmic contact with p-type II-VI nanostructures due to the formation of highly conductive Cu2S interfacial layer,39 were defined by photolithography as the source and drain contacts, while the Si substrate served as the global back gate. Figure 2b depicts the current versus voltage (I-V) curve of the CdS NR after decoration via spin-coating, and I-V curves for the as-synthesized CdS NR and the MoO3 NDs layer are measured for comparison. The as-synthesized CdS NR possesses an extremely low conductance (conductivity) of 1.8×10-11 S (9.6×10-4 S m-1), owing to the low carrier concentration in NR and the large contact barrier between the NR and Cu/Au electrodes. Similarly, the MoO3 NDs layer, prepared by directly drop casting 20 µL MoO3 solution (0.1 wt%) onto blank Cu/Au electrodes, also shows a low conductance of 3.3×10-10 S. In contrast, due to charge transfer between CdS NR and MoO3 NDs, the conductance (conductivity) of the decorated CdS NR increases drastically by more than 7 orders of magnitude to 2.0×10-4 S (1.1×104 S m-1) compared to the intrinsic CdS NR. The conductance of CdS NR is observed to strongly depend on the concentrations of MoO3 solutions, and decrease with decreasing MoO3 solution concentration (or surface coverage of NDs on NR surface) (Figure 2c). The devices with different channel lengths of 8 and 21 µm exhibit the same tendency except for the difference in conduction current. Drop-casting of the MoO3 solution on CdS NR gives rise to one order of magnitude increase in conductance compared to the spin-coating processing, due to the complete coverage of MoO3 NDs on NR surface (Figure S4, Supporting Information) in the former.


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However, the lack of thickness control in the drop-casting processing is a disadvantage, producing a thick MoO3 NDs layer on NR surface, which is deleterious to photovoltaic devices due to strong light absorption. Besides CdS NRs, CdS NWs can also be doped via similar decoration of MoO3 NDs (Figure S5, Supporting Information), indicating the generality of the method for p-type doping of CdS nanostructures. Figure 2d depicts the electrical transport charecteristics of the MoO3 NDs-decorated CdS NR by applying a gate voltage (VGS) on Si substrate. Without decoration, the CdS NR shows a low source-drain current (IDS) increasing with increasing VGS, which is consistent with n-type conductivity, and leads to an electron mobility (µe) of 0.35 cm2 V-1 s-1 and an electron concerntration (ne) of 7.5×1013 cm-3. In contrast to the intrinsic CdS NR, IDS of MoO3 NDs-decorated CdS NR decreases with increasing VGS, which is consistent with a typical p-type metal-oxide-semiconductor field-effect transistor (MOSFET), revealing the p-type nature of the decorated NR. The hole mobility (µh) and hole concentration (nh) are deduced to be 525 cm2 V-1 s-1 and 8.5×1019 cm-3, respectively. The high nh manifests that degenerated p-type doping of CdS NRs has been achieved. As a typical transitional metal oxide with a high work function (6.9 eV), MoO3 is often used as a hole injection layer in organic semiconductor devices such as organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs).40 Recent investigations reveal the strong charge transfer between MoO3 and inorganic semiconductor nanostructures.41,42 Upon surface decoration, the work function difference between MoO3 NDs and CdS NRs leads to injection of abundant holes from MoO3 NDs into CdS NRs. The enhanced conductivity as well as charge inversion from n-type to p-type conductance in NRs are attributed to the charge transfer effect. Meanwhile, the hole injection results in the accumulation of excess delocalized holes in CdS NRs and consequently the upward energy level bending from the bulk to surface. This


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phenomenon can be detected by X-ray photoelectron spectroscopy (XPS) characterization (Figure 3a, b). The positions of Cd 3d and S 2p peaks shift toward lower energies after NDs decoration, i.e. Cd 3d3/2 shifts from 412.5 to 412.2 eV and Cd 3d5/2 from 405.7 to 405.4 eV, while S 2p1/2 shifts from 163.3 to 162.7 eV and S 2p3/2 from 162.1 to 161.6 eV. The downshift of the peaks is attributed to the p-type doping process, which shifts the valence band of CdS NR toward the Fermi level. In a control experiment, MoO3 film was deposited by conventional thermal evaporation onto CdS NRs. Subsequent electrical measurements showed the MoO3 film had a much weaker doping effect on CdS NR, despite a film thickness of 20 nm (Figure S6a, Supporting Information). This result can be attributed to the large amount of oxygen vacancies in the high vacuum-evaporated MoO3 film (Figure S6b, Supporting Information), which results in the decrease of MoO3 work function and consequently weaker surface charge transfer.43 In contrast, the MoO3 NDs prepared by the solution process are nearly stoichiometric and can retain the high work function, thus offering superior doping performance. Kelvin probe force microscopy (KPFM) detection was performed to visualize the charge transfer in MoO3 NDs decorated-CdS NRs.44,45 As illustrated in the top image of Figure 3c, one half of a single CdS NR was decorated using 0.1 wt% MoO3 NDs via spin-coating (detailed decoration process in Figure S7, Supporting Information). AFM topography, the middle image in Figure 3c, shows no presence of morphology variation or other specific features after decoration. However, a clear contrast difference between the two halves of the CdS NR can be observed in the Kelvin potential image (in the bottom image of Figure 3c), with the higher potential region being the part of NR decorated with MoO3 NDs. A line scan analysis, Figure 3d, reveals a change in the Kelvin voltage of ca. 40 meV at a tip position of 4 µm. The lower Kelvin voltage for the NDs-decorated region indicates a decrease in surface potential, which is caused by the


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hole transfer from MoO3 NDs to CdS NR. Note that a peak of Kelvin voltage is observed at a 2 µm tip position. The nature of this peak voltage is not clear, but we suppose that it is likely caused by the surface contamination of photoresist on the NR. Photoresist was used to protect the left part of the NR during MoO3 NDs decoration, but subsequently was removed by actone to perform KPFM measurement (Figure S7, Supporting Information). The residual photoresist on the NR surface due to incomplete removal may cause the fluctuation of the Kelvin voltage. Also, some MoO3 NDs will fall off from the NR surface during the lift-off of photoresist, therefore the change in Kelvin voltage is underestimated and lower than the actual value. In spite of this, the KPFM detection clearly manifests the charge transfer between MoO3 NDs and CdS NR. To gain more insight into the charge transfer between MoO3 NDs and CdS NRs, we calculated the difference charge density (∆ρ) of the CdS surface after NDs decoration based on the firstprinciple method. ∆ρ is defined by the following equation: ∆ρ = ρMoO3/CdS NR – ρCdS NR – ρMoO3, where ρMoO3/CdS NR, ρCdS NR and ρMoO3 represent the charge densities of the full system, the CdS NR, and the isolated MoO3 molecules, respectively. The preferential growth orientations of NRs in this work are [001] (Figure S1, Supporting Information), therefore the side surfaces can be determined to be (100) and (110), on which the MoO3 NDs will be decorated, as illustrated in Figure 4a. Figure 4b shows the optimized configuration of one MoO3 molecule-decorated CdS (100) surface, while the corresponding contour map of ∆ρ values is plotted in Figure 4c. The regions of electron accumulation and depletion are displayed in red and blue colors, respectively, in the map. A strong electron accumulation is present around the O atoms of MoO3 molecule, while the electron depletion appears around the Cd atoms on the CdS (100) surface. This phenomenon suggests that the adsorbed MoO3 molecule gains electrons, whereas the CdS NR loses electrons. In addition, on the basis of Mulliken population analysis, the charge of the as-


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decorated CdS NR is 0.19 e, indicating that a fractional positive charge of 0.19 e is injected into the CdS super cell, as proved in the experiment. Since a 3 nm MoO3 ND consists of several hundreds of MoO3 molecules, the sizes of the MoO3 clusters are further increased to contain two and three molecules in the simulation. Also, the CdS (110) surface decorated with one MoO3 molecule is calculated. Notably, all simulations give analogous results (Figure S8 and Table S2, Supporting Information), corroborating the high-efficiency charge transfer between CdS NR and MoO3 molecules. Flexible PV devies are essential components for future light-weight and wearable electronics.46 Here, we further investigate the application of CdS NRs in flexible PV devices by constructing CdS NR homojunctions on flexible substrates via MoO3 NDs decoration. As illustrated in Figure 5a, CdS NR-homojunction devices were fabricated on PET substrate by decorating MoO3 NDs on one-half parts of the CdS NRs. In and Cu/Au were used as ohmic contacts respectively for intrinsic CdS NR, i.e. the n-type side, and for MoO3 NDs-decorated CdS NR, i.e. the p-type side (detailed fabrication process see Figure S9, Supporting Information). Figure 5b shows a photograph of the mechanically flexible CdS NR-homojunction devices on PET, along with an optical microscope image of an individual cell in the inset. The half part of the CdS NR underneath the photoresist (PR) can be clearly seen, indicating that the photoresist will transmit the incident light. Therefore, the total area of the CdS NR in the device channel can contribute to the photocurrent. The black curve in Figure 5c depicts the I-V curve of an optimized device in the flat configuration under the light illumination of 1.9 mW cm-2. The open-circuit voltage (VOC) and fill factor (FF) are determined to be 0.55 V and 73.02 %, yielding a PCE of 5.48% for the device. Table S1 shows that the PCE of 5.48% of the flexible CdS NRhomojunction device surpassed that of most of the heterojunction solar cells and is among the


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best values reported so far. It is known that the performance of a PV device is dominated by the junction quality, and the carrier recombination caused by junction defects is an important factor for degradation of device performance. The superior performance of the CdS NR-homojunction PV device clearly indicates the high efficacy of the MoO3 NDs decoration approach, which ensures the fabrication of homojunctions with less junction defects and thus minimum carrier recombination. To assess the performance change under strain stress, the device was bended to different radii from 26 to 5 mm. Figure 5c shows that VOC and FF change little after bending, whereas short cricuit current (ISC) decreases with decreasing bending radius. As a result, PCE of the device decreases to 3.92 % at a bending radius of 5 mm, which is ~70% of that of the flat device. Remarkably, the PCE of the device can recover 4.67% or 85% of the original value, when it is returned and measured in the flat configuration, as shown in Figure 5d. And the performance can remain nearly unchanged after up to 100 times of bending. This result demonstrates the high robustness of the flexible PV device against bending. The slight decrease in PCE after first bending may be attributed to the increased contact resistance between metallic electrodes and CdS NR, since the series resistance Rs increases from 1.4×108 Ω measured in the flat configuration to 1.7×108 Ω measured at a bending radius of 5 mm. The device performance was further evaluated by changing the light intensity (Figure S10, Supporting Information). Interestingly, the device can function well under a weak light ranging from 0.06 to 1.9 mW cm-2 owing to a large parallel resistance (Rsh = 1011 Ω), indicating its potential for low-illuminaition application, such as indoor condition. In addition, both ISC and VOC increase with increasing light intensity and reach 6.1 nA and 0.60 V, respectively, under a light intensity of 100 mW cm-2.


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Though the nanostructure-based PV devices can offer higher integration level for nanooptoelectronics, the power of a single cell is limited by its small size and normally is inadequate to drive a practical device. To bypass this difficulty, multiple cells can be connected in series or in parallel to provide a higher output power. Figure 6a and 6b show the optical images of CdS NR-homojunction PV devices with multi-cells connected in series and in parallel configurations, respectively. Figure 6c shows the PV behaviors of cells connected in series, revealing that the VOC is proportional to the cell number, reaching 2.05 V for four cells in series. The high uniformity of the devices is reflected by the high FF, which varies in a small range of 66.571.3% for 1-4 cells in series. It is observed that the ISC decreases somewhat with increasing cell number. This is mainly attributed to the variation in width of the CdS NR from left end to right end; the width of CdS NRs tends to shrink towards the growth tips, as shown in Figure S1a in supporting information. Measurements on the cells connected in parallel reveal that ISC increases sharply from 57 pA for one cell to 1296 pA for six cells (Figure 6d) in parallel, while the VOC keeps nearly identical and FF changes only slightly. These results clearly demonstrate the superior performance of CdS NR-homojunctions for integrated nano-optoelectronics. In summary, we have developed a new strategy to achieve efficient p-type doping in CdS NRs via surface charge transfer using spin-coated MoO3 NDs. The doped p-type CdS NRs possessed a hole concentration up to 8.5×1019 cm-3 and a hole mobility as high as 525 cm2 V-1 s-1. Efficient charge transfer between CdS NRs and MoO3 NDs was verified by XPS and KPFM characterizations as well as first-principal calculations. Selective deposition of NDs on one-half parts of the NRs led to the realization of CdS NR p-n homojunctions. Owing to minimal defects at the junction interface, the p-n homojunction-based flexible PV devices exhibited high VOC and FF, yielding a PCE value of 5.48%. This PCE is among the best values for CdS nanostructure-


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based PV devices. The devices possessed excellent flexiblity with performance remaining nearly unchanged after 100 times of bending. Higher power output could be obtained in multi-cell devices made by connecting cells in series or in parallel, revealing the great potential of the CdS NR homojunctions for integrated nano-optoelectronics. Various improvements of the flexible CdS NR-homojunction solar cell may be envisioned including the careful control of doping level in the NRs to ensure a high-quality p-n junction and the use of ternary compound NRs like CdSxSe1-x NRs to enhance the light absorption at long wavelength. The present method provides a facile approach for complementary doping in II-VI semiconductors, and an efficient route for developing high-performance optoelectronic devices based on the II-VI nanostructures.

Experimental Section Synthesis of CdS NRs: Synthesis of CdS NRs was conducted in a horizontal quartz tube furnace via thermal evaporation. Briefly, 0.5 g CdS powder (Alfa Aesar, 99.999%) was loaded on an alumina boat at the center of a tube furnace, then Si substrates covered with a thin layer of Au (5 nm) catalyst were placed at the down-stream positions ~5 cm away from the CdS source. After the tube was evacuated to a pressure of 0.02 mbar, a high-purity mixed gas of Ar and H2 (5%) was introduced into the tube at a rate of 30 standard cubic centimeter per minute (SCCM). Then the CdS powder was rapidly heated to 870 oC at a rate of 20 oC min-1. During growth, the pressure in the reaction chamber was maintained at 0.1 bar. After a growth duration of 2 h, the yellow product was collected from the Si substrates. Preparation of MoO3 solution and MoO3 NDs-decorated CdS NRs: To prepare the MoO3 solution, 0.015 g MoO3 powder (99.999%, Strem Chemicals, Inc.) was dissolved in 15 mL of deionized water. The solution was put in a 70 oC water bath under magnetic stirring. Sparingly


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soluble MoO3 aqueous solution was formed by hydrolysis of MoO3 in H2O as: MoO3 + H2O → (MoO4)2- + 2H+. The MoO3 solution (0.1 wt%) was further diluted to obtain the solution with a concentration of 0.05, 0.025, 0.0125, and 0.01 wt%, respectively. To decorate CdS NRs, 20 µL MoO3 solution was spin-coated (3000 rpm for 30 s) or drop-casted onto the CdS NRs predispersed on substrates. MoO3 NDs would precipitate from the aqueous solution and deposit on the CdS NRs during solution evaporation. Material characterization: Scanning electron microscope (SEM, FEI Quanta 200 FEG) and TEM (FEI Tecnai G2 F20 S-TWIN) were used to characterize the morphologies and structures of CdS NRs, MoO3 NDs, and MoO3 NDs-CdS NR composite. X-ray diffraction (XRD, PANalytical Empyrean) and selected-area electron diffraction (SAED) were used to determine the crystal structures. XPS (Kratos AXIS UltraDLD) analysis was performed using a monochromatic Al Kα source (1486.6 eV). KPFM (Veeco, Multimode V) was used to measure the local work function of the sample surface. Device fabrication and characterization: To study the electrical characteristics of CdS NRs after MoO3 NDs decoration, bottom-gate FETs based on individual CdS NRs were constructed as follows: the as-synthesized n-type CdS NRs were uniformly dispersed on SiO2 (300 nm)/n+-Si (resistivity

Nanodots Decorated CdS Nanoribbons for High-Performance

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