Hole transport layers (HTLs) have a significant role in the performance of organic and organic-inorganic solar cells. In this experiment, we have investigated HTLs for Pb-Sn binary perovskite solar cells (PSCs) to maximize the power conversion efficiency (PCE). CuI, PTAA, and PEDOT:PSS were chosen as HTLs to fabricate the MAPb0.75Sn0.25(I0.50Br0.50)3 perovskite solar cells. The solar cells were fabricated using an inverted p-i-n structure where we used ITO/HTL/Perovskite/C60/BCP/Al materials stack. For PSCs containing CuI, PTAA and PEDOT:PSS as HTL, we obtained the PCE of 3.81%, 3.11 and 6.5%, respectively, with unchanged other experimental condition. Also, PEDOT:PSS HTL-based solar cells deliver higher short circuit current of 16.37 mA/cm2 compared to CuI and PTAA HTL based binary perovskite solar cells. For these binary PSCs, PEDOT:PSS is the best choice to maximize power conversion efficiency.
The availability of printable dielectric materials and their printability is one of the major roadblocks to printed flexible electronics. Here, we report the performance of fully printed field-effect transistors using polyvinyl alcohol (PVA) as dielectric and carbon nanotube (CNT) as a semiconducting layer. As fewer numbers of research are available on printed PVA films, here we investigate ink formulation and printing parameters for PVA and their effects on device performances. Aerosol jet Printer was used to obtain a highly dense CNT network and pinhole-free thin PVA dielectric layer that resulted in a high on/off ratio and drain current. This completely printed transistor with polymer dielectric will be a great contribution to flexible electronic devices.
Anti-solvent-free one-step deposition of perovskite thin film shows promising potential for application in slot-die or roll-to-roll mass-fabrication processes of perovskite solar cells. The continuous coverage was confirmed by PV response of devices made using the one-step deposition process. In this work, we have developed a process to deposit MAPb0.75Sn0.25(I0.5Br0.5)3 perovskite thin films without anti-solvent adding MAAc to the ink. By varying the Br content of the perovskite precursor, we were able to tune the bandgap. Fabricated solar cells with the structure ITO/CuI/ MAPb0.75Sn0.25(I0.5Br0.5)3 /C60/BCP/Al with PCE of 4.59% show the path of the fabrication process of antisolvent-free tin-lead-based solar cells
In recent years, PPDT2FBT is getting researchers’ attention due to its applications in solar cells and optoelectronic devices. Although the main applications of this material are based on the optical properties. However, the optical dispersion of this material has not been studied yet over the UV and visible spectral range. We report the optical properties of PPDT2FBT for the wavelength range of 300 nm to 900 nm using a variable angle spectroscopic ellipsometry (SE). The refractive index (n) and extinction coefficient (k) of spin coated PPDT2FBT thin films were determined at room temperature. Glass of known optical properties was used as the substrates for convenience. To build an optical model the surface morphology was studied using atomic force microscopy (AFM). Then an optical model was developed based on the extracted properties. The optical properties were found to be consistent with the UV-Vis data. The bandgap was estimated from the absorption properties. Finally, the developed ellipsometry model was used for thickness measurement of PPDT2FBT thin films. The measured data agreed well with the data collected using other direct thickness measurement techniques of the same thin film. This developed model can be useful for designing effective optoelectronic devices as well as measuring the thickness of thin films in a nondestructive way.
A novel method of preparing magnetic ink belonging to the class of ferrofluids which contains magnetic particles with a polar surface-active agent is disclosed. The magnetic material belongs to the group known as magnetite (Fe3O4), typically to those with γ-Fe2O3 and their likes. Ni-Zn ferrite and Mn ferrite inks were prepared using this method. The inks have a PH value and total dissolved solute of about 6.3, 3.78 mS and 5.9, 4.2 mS respectively, and a viscosity of about 7 cPa, 7.4 cPa respectively. The saturation magnetization of Mn ferrite ink at 300K was 62 emu/cm3. This lower value of the saturation magnetization of Mn ferrite compared to the bulk is because of the shell-core structure of the surfactant coated ferrite particles. The inks were used to prepare various thicknesses ranging from 0.5um to 20um of both Ni-Zn ferrite and Mn ferrite thin films. The surface morphology of the thin film was observed using Atomic Force Microscopy (AFM), showing a compact, dense and relatively smooth film. The microstrip transmission line permeameter approach was used to extract the permittivity and permeability of the thin film samples within the frequency range of 10MHz-1GHz. A relative permeability of 2 was measured. The developed ink and thin film are promising for future magneto-optical applications.
This paper presents a novel approach for the design and fabrication of graphene-based and fully printed single patch antennas. Graphene ink for inkjet printing is prepared by dispersing graphene nano flakes (12 nm) into terpineol and cyclohexanone solvents, and ethyl cellulose surfactant. The viscosity of the as-synthesized graphene ink is found to be 5.5 cP which is compatible with the inkjet printing. Raman spectroscopy is used to provide a structural fingerprint of the printed graphene flakes. Additionally, the printed graphene patterns become conductive for 35-40 printed layers. The physical structure of the single patch antenna consists of a printed transmission line and a single patch. The resonant frequency for the inkjet-printed graphene single patch antenna on DuPont Kapton FPC Polyimide substrate is 5 GHz, which is consistent with the design. The performance of printed graphene antenna is compared with the transferred graphene and printed silver antennas. The printed graphene antenna shows a better gain of 4.47 dBi and efficiency of 70%.
This paper presents the design and fabrication of inkjet printed graphene field-effect transistors (GFETs). The inkjet printed GFET is fabricated on a DuPont Kapton FPC Polyimide film with a thickness of 5 mill and dielectric constant of 3.9 by using a Fujifilm Dimatix DMP-2831 materials deposition system. A layer by layer 3D printing technique is deployed with an initial printing of source and drain by silver nanoparticle ink. Then graphene active layer doped with molybdenum disulfide (MoS2) monolayer/multilayer dispersion, is printed onto the surface of substrate covering the source and drain electrodes. High capacitance ion gel is adopted as the dielectric material due to the high dielectric constant. Then the dielectric layer is then covered with silver nanoparticle gate electrode. Characterization of GFET has been done at room temperature (25°C) using HP-4145B semiconductor parameter analyzer (Hewlett-Packard). The characterization result shows for a voltage sweep from -2 volts to 2 volts, the drain current changes from 949 nA to 32.3 μA and the GFET achieved an on/off ratio of 38:1, which is a milestone for inkjet printed flexible graphene transistor.
We simulate the pulse compression around 1550 nm using one stage highly anomalous dispersive photonic crystal fibers, including silica-core photonic crystal fiber with a dispersion value of 600 ps/nm/km and air-core photonic bandgap fiber with a dispersion value of 100 ps/nm/km. A 1.64ps pulse with peak power of 500kW is compressed down to 0.136 ps with a compression factor of 12 by 4.3 m photonic bandgap fiber. Experimental results show that a 1.64 ps pulse is compressed down to 0.357 ps with a compression factor of 4.6 by 1.7 m photonic crystal fiber.
Printing technique is a simple and cost effective method to produce electronics. In this
work, self-aligned carbon nanotube thin-film transistor based phased shifter has been used to
fabricate a 1x4 phased array antenna system on a flexible substrate using a combination of ink-jet
printing and stamping techniques. The radiation pattern is measured for different steering
angle conditions. Measured and simulated far field radiation patterns are reported, and both data
sets agree well with each other. The efficiency the 2-bit 1x4 PAA system is calculated to be 42%
including the loss of transmission line, FET switch, and coupling loss of RF probes.
Bending tests of carbon nanotube thin-film transistors on flexible substrate have been characterized in this
paper. The device channel consisting of dense, aligned, 99% pure semiconducting single-walled carbon nanotubes
(SWCNT) are deposited using dip-coat technique on sacrificial substrate and then transferred on to the device substrate.
Ink-jet printing technique is used to form the source, drain and gate electrodes using silver ink. A novel source-drain
contact formation using wet droplet of silver ink prior to CNT thin-film application has been developed to enhance
source-drain contact with the CNT channel. Bending test data on CNT-TFT test structures show minimal change (less
than 10%) in their performance. To reduce the device performance variation due to bending, flexible electronic circuit is
designed such that vertical device orientation is used for backward bending and horizontal orientation is used for forward
bending.
We present a flexible active 2-bit 2-element phased-array antenna (PAA) fully fabricated using ink-jet printing
technology. High speed carbon nanotube (CNT) based field effect transistors (FETs) function as switch in the true-time
delay line of the PAA. The 2-bit 2-element active PAA is printed out at room temperature on 100μm thick Kapton
substrate. The FET switch works well for 5GHz RF signals. An ON-OFF ratio of over 100 is obtained at a low Vds bias
of 1.8V. The measured azimuth beamsteering angles of PAA agree well with simulation values.
In this paper, we report the theoretical study of polymer-based photonic crystals for laser beam steering
which is based on the superprism effect as well as the experiment fabrication of the two dimensional
photonic crystals for the laser beam steering. Superprism effect, the principle for beam steering, was
separately studied in details through EFC (Equifrequency Contour) analysis. Polymer based photonic
crystals were fabricated through double exposure holographic interference method using SU8-2007. The
experiment results were also reported.
We demonstrate single RF beam transmission and reception of an X-band phased array antenna using highly dispersive photonic crystal fiber (PCF) based true-time-delay (TTD) lines. The dispersion coefficient of the fabricated fiber is as high as -600ps/nm/km at a wavelength of 1545nm. Coupling between a dispersion shifted fiber (DSF) and the fabricated PCF is performed by using an ultra high numerical aperture (UHNA) intermediate fiber, which helps in achieving a good coupling efficiency and keeping the insertion loss of the delay lines to under 3.5dB. Using the PCF-TTD network, we report the transmission of 8.4GHz signal at 7.40 and 12GHz signal at 21.20 by tuning the laser wavelength to 1547.72nm and 1552.52nm respectively. Single beam receiving capability is also demonstrated by accurately detecting 8.4GHz signal coming from -7.40 and 12GHz signal coming from -21.20 by tuning the wavelengths to 1547.72nm and 1552.52nm respectively..
In this paper, a highly dispersive pure silica photonic crystal fiber is designed and fabricated with maximum chromatic
dispersion value of about -600 ps/(nm·km) around 1.55 μm wavelength region. This kind of a photonic crystal fiber
structure is suitable for high dispersion application in photonic crystal fiber array based phased array antenna systems.
A four-element true-time delay module is constructed using the fabricated highly dispersive photonic crystal fibers. The
true time delay value of 10.5m PCF is characterized to provide maximum delay of 31.3ps with 32nm optical wavelength
tuning range, which is sufficient to scan from -45° to 45° for a 4-element PAA subarray having 1.3cm spacing. A
multiple-beam optical beamformer is designed based on the fabricated highly dispersive photonic crystal fibers. The
true-time delay beamformer can be programmed to continuously sweep the antenna aperture independently for multiple
RF beams. Since the dispersion of the fabricated photonic crystal fibers is as high as -600 ps/nm•km at 1550 nm,
compared to telecom SMF-28 that has a dispersion parameter of 18 ps/nm•km, the length of delay line is reduced by a factor of 33.
A 4-bit polymer optoelectronic true time delay device is demonstrated. The device is composed of monolithically integrated, low loss, passive polymer waveguide delay lines and 2x2 polymer thermo-optic switches. Waveguide junction offsets and air trenches simultaneously reduce the bending loss and device area. Simulations are used to optimize the trench and offset structures for fabrication. The 16 time delays generated by the device are measured to range from 0 to 177 ps in 11.8 ps increments. The packaged device has an insertion loss of 14.5 dB and the delay switching speed is 2 ms. The delays generated by the device are suitable for steering a 1D or 2D sub-array of an X-band phased array antenna system.
A novel optoelectronically-controlled wideband 2-D phased-array antenna system is demonstrated. The inclusion of WDM devices makes a highly scalable system structure. Only (M+N) delay lines are required to control a M×N array. The optical true-time delay lines are combination of polymer waveguides and optical switches, using a single polymeric platform and are monolithically integrated on a single substrate. The 16 time delays generated by the device are
measured to range from 0 to 175 ps in 11.6 ps. Far-field patterns at different steering angles in X-band are measured.
Continuously tunable optical true time-delay (TTD) modules based on dispersion-enhanced photonic crystal fibers (DEPCFs) are demonstrated to provide continuous microwave squint-free beam scanning for an X-band (8 to 12 GHz) phased-array antenna (PAA) system. The dispersion of the fabricated photonic crystal fibers (PCFs) is as high as –600 ps/nm km at 1550 nm. By employing PCFs to increase the dispersion, the TTD module size can be proportionally reduced. The time delay is continuously tunable from –31 ps to 31 ps between adjacent delay lines by tuning the laser wavelength continuously from 1528 to 1560 nm. The far-field radiation patterns of a 1×4 subarray were measured from –45 to 45 deg scanning angles. Squint-free operation is experimentally confirmed. Wavelength conversion is also demonstrated to confirm that time-delay information can be successfully transferred from one wavelength to the other without being changed, which is suitable to be implemented in 2-D phased-array antenna systems. The TTD formation idea presented is suitable for not only the X band, but also the other higher microwave frequencies, such as the K band.
A wavelength-controlled continuous beam-steering four-element X-band (8- to 12-GHz) phased array antenna system is presented. The system is based on the continuously tunable optical true-time-delay technique. Dispersion-enhanced waveguide holograms were proposed and used to fabricate the optical true-time-delay devices. The devices are characterized both theoretically and experimentally. The wavelength of a laser was tuned within the system to get continuously tunable true time delay. The time delay was measured for a wavelength tuning range from 1537 to 1547 nm in 10-nm steps. The far-field radiation patterns of the antenna system were measured at 9 and 10.3 GHz, and they showed no beam squint. The true-time-delay formation idea presented here is suitable for not only X-band, but also for higher microwave frequencies, such as K-band.
Photonic crystal based devices received attention in recent years. Based on the superprism effect in photonic crystals, beam steering devices can be made with properties sensitively dependent on the wavelength and incident angle of light. One stumbling block for designing superprism-based demultiplexers is that current numerical methods have difficulties in simulating a practical superprism device with commonly available computational facilities. Examining the superprism effect in a more general perspective, we previously developed a rigorous theory to solve the photonic crystal refraction problem for any surface orientation and any lattice type. This paper will compare our theory with other methods with regard to computational workload to demonstrate the advantages of our theory. Excellent agreement of numerical results with the transfer matrix method is also demonstrated. Heuristic discussions on the beam width variation and energy conservation are presented. A technique for direct computation of the dispersion surface is compared with the methods that combine a photonic band solver with certain interpolation or 1D-searching techniques.
A thermo-optic switch using total internal reflection waveguide was fabricated for optical true time delay. Experimental result shows that the crosstalk in the bar state is as low as -42dB and the total insertion loss is only -4dB at the wavelength of 1.55μm. A power consumption of 130mWand switching speeds of 2ms are obtained as well, which makes the device qualified to be used in the application of optical true time delay.
The design and fabrication of a polymer optical waveguide based true time delay (TTD) device is described. Optimization of the fabrication process decreased the waveguide propagation loss from more than 1.55 dB/cm to 0.38 dB/cm at a wavelength of 1.55um. Waveguide bend loss structures were fabricated and measurement results were compared to simulations. A bend radius of 3 mm provides low insertion loss and small device size. 2x2 thermo-optic TIR switches were fabricated with insertion losses of 2.8 dB. A 4-bit TTD device for use with a 4x4 sub-array of a 10GHz phased array antenna was calculated to have an insertion loss of 23.88 dB.
Photonic crystal based structures have been considered for optical communication applications. A class of novel symmetric structures consisting of cavities and waveguides have been proposed to serve as optical add-drop multiplexers. Light transfer processes in these structures are analyzed briefly. The problem of deviating from the perfect accidental degeneracy is addressed for practical designs, and the backscattering intensities are shown low for the slight deviations. Anomalous light refraction at a surface of a photonic crystal has also been studied. The limitations of prior theoretical methods for the transmission problem are discussed. An outline of a new analytic theory that overcomes these limitations is presented. Photonic crystals are fabricated on polymer multi-layer films and integrated with conventional channel waveguides.
A novel reconfigurable true-time delay feed for phased-array antennas working from X to Q (8-50GHz) frequency bands is presented. The reconfigurable optical true-time delay feed, employing monolithic integration of polymer waveguide delay lines and polymeric optical switches, has great advantages in providing power efficient, lightweight, and small size features. Optical switch technique provides large delay selections enabling the module to operate in ultra-broad radar bands. Polymer waveguides with optical propagation loss of less than 0.9dB/cm were achieved at 1550nm. 2X2 thermo-optic switchs as fast as 1ms were fabricated with an excess insertion loss of 0.5 dB in the “switching state” and 1.5dB in the “non-switching state”. Reconfigurability of the true-time delay line was demonstrated through accurate time delay measurement.
The holographic-grating based wavelength-controlled true-time-delay devices are presented in the paper. The optical true-time-delay can be continuously controlled by continuously tuning the wavelength of a single laser within the devices. The dispersion ability of the devices is greatly enhanced by increasing the diffraction angles of the holographic gratings. The fabricated true-time-delay devices work within 1550nm region. The loss performance of the devices were calculated and measured. The wavelength-controlled true-time-delay was also characterized both theoretically and experimentally.
We analyze the abnormal refraction and propagation when a light
beam of finite and practical width enters a photonic crystal from a
uniform medium. The beam propagation in the photonic crystal is
very complex, and in many cases, is beyond the realm of refraction
(even with a renormalized refractive index given by photonic band
calculation). Generally, light propagation is restricted to a
triangular region (or a fan), although the light may not fill the
whole triangle, nor is the light intensity uniform in the triangle. It is found beam divergence does not have a definite connection with
the fan shape of the region of light propagation, in contrast to
dynamic X-ray theory. A new origin of the fan shape is suggested.
Also simulations indicate that at microscale, a narrow light beam
may zigzag in a photonic crystal with sufficiently high index contrast. An application of this phenomenon is to make a wide angle bend for waveguides. The designed bending structure has low loss and matches the mode size of a typical single-mode waveguide for fiber-optic communications. Our simulations are based on two-dimensional photonic crystals.
Wavelength-controlled true-time delay modules based on the dispersive hologram-waveguide are presented here to provide continuous beam-scanning for a X-band phased-array antenna system. The true-time delay modules operating in the 1550nm region were fabricated with continuously tunable time delays from 5ps to 64ps. All-optical wavelength conversion in the semiconductor optical amplifiers was proposed in the system to extend the beam-scanning scope from one dimension to two dimensions. The wavelength-controlled time delays were measured across the x-band (8-12GHz) in the experiment.
A continuously variable optical true time delay module, based on substrate-guided-wave and holographic optical elements, is designed and fabricated. The dispersion effect of volume holographic gratings is combined with a novel structure to obtain continuously variable time delay intervals from tens of picosecond down to sub-picosecond, which can be employed for K-band (18 GHz - 26.5 GHz) and Ka band (26.5 GHz - 40 GHz) phased-array antennas. The insertion loss of the packaged module is 10 dB, including fan-out loss and propagation loss, while the non-uniformity of insertion loss is within 0.6 dB among all channels. The crosstalk among channels is less than -40 dB. An optical true time delay module is designed to provide delay signals for -60 degrees to +60 degrees continuously steering of an eight-element K-band phased-array antenna system. Antenna field patterns are simulated with the change of optical wavelengths. The demonstrated architecture can be used in both the transmitting and the receiving modes and can be easily scaled up for large arrays.
A 2D true-time delay (TTD) module for phased-array antennas (PAAs) is presented, which is based on substrate-guided wave elements. We use substrates of different thickness to get time delays as small as needed. We also use coated wedge to substitute input hologram element to decrease losses up to 60%. Also, a step is designed to obtain 0 degree steering which is impossible for packaging in the previous design. We designed special delay steps to avoid the side lobe caused by the limitation of the distance between adjacent antenna elements. The simulation results were given for the far- field radiation pattern of PAA controlled by this module. Experimental results of the TTD module are shown in both 2D and 3D images.
We have proposed and designed a photonic true-time delay (TTD) steered phased-array antenna system that can work at
high RF frequency with high angular resolution. Several elementary techniques have been studied and developed, including
an optical realization of the Blass matrix based on our substrate-guided wave fanout structure, switching operation of
wideband MSM and PIN photodetectors, and heterodyne RF signal generation. A design for the system demonstration that
has the bandwidth from 18 to 26GHz is reported.
An optical realization of the Blass matrix based on a substrate-guided wave true-time delay (TTD) module has been proposed and designed for a photonic phased-array antenna (PAA) system, which will operate from 18 to 26 GHz. It is the highest RF frequency range for system level that has been reported until now. A 3 X 8 triangular array lattice will be used and all the elements divided into 8 sub-arrays controlled optically by true-time delay signal. To avoid the squint error caused by the phase control within the subarray, we propose a new squint-free subarray steering technique, which is based on the operation of the true-time delay signals provided by our new optical TTD Blass matrix. The simulation result is given for the far-field radiation pattern of photonic PAA controlled by this technique and no squint is found. We also demonstrate an optical heterodyne system for photonic RF signals generation with conversion efficiency that approaches the theoretical limit.
The Non-linear Distortion(NLD) in QAM channel of AM/QAM lightwave systems is mainly caused by the clipped Gaussian noise. We use an asymptotic distortion spectrum of clipped Gaussian noise estimating the nonlinear distortion power in AM/M-QAM lightwave system. Also the BER of QAM signal is calculated based on the estimated NLD power. We also compute the BER of QAM signal with the changing of QAM signal power to Gauss noise power ratio(SNRg) and QAM signal power to NLD power ratio(SNLD).
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