Search

Organic-inorganic hybrid perovskites as promising light-harvesting materials have been the focus of scientific research and development of photovoltaics recently. Especially, metal halide perovskites currently become one of the most competitive candidates for the fabrication of solar cells with record certified efficiency over 25%. Despite the high efficiency, many fundamental questions remain unclear and need to be addressed at both the material and device levels, such as weaker stability, poorer reproducibility, easier degradation influenced by water, oxygen, thermal factors, and so on. Based on recent reports, interfacial engineering plays a crucial role in controlling the behavior of the charge carriers and in growing high quality, defect-free perovskite crystals, therefore helping to enhance device performance and operational stability. However, little attention has been paid to the interface interaction mechanism among carrier transport layers and perovskite active layer. It is extremely urgent to explore the perovskite interfaces in details and to find out how its interface structure is relative to the efficiency and hysteresis in perovskites solar cells. Based on the Shanghai Synchrotron Radiation Facility (SSRF), we have established an advanced perovskite photovoltaic device preparation and in-line test system, developed a series of unique surface diffraction analysis methods based on ex situ and in situ grazing incidence X-ray diffraction (GIXRD), and reported a large number of novel synchrotron radiation results on crystallization of the perovskite photovoltaics films. Our main investigations are aimed to deeply in-situ study the perovskite film growth dynamics using synchrotron radiation GIXRD technology in combination with a customized mini online glove box (c(H2O,O2)

Naphthalene diimide (NDI)-based polymer N2200 is a promising organic polymer acceptor for all-polymer solar cells (all-PSCs), but its inherent shortcomings like poor extinction coefficient and strong aggregation limit further performance optimization of all-PSCs. Here, a series of random copolymers, PNDI-Px, were designed and synthesized by introducing porphyrin unit into NDI-based polymer as acceptors for all-PSCs. These random copolymers show a higher absorption coefficient and raised the lowest unoccupied molecular orbital (LUMO) energy levels compared to N2200. The crystallinity can also be fine-tuned by regulation of the content of porphyrin unit. The random copolymers are matched with polymer donor PBDB-T for the application in all-polymer solar cells. The best power conversion efficiency (PCE) of these PNDI-Px-based devices is 5.93%, ascribed to the overall enhanced device parameters compared with the N2200-based device. These results indicate that introducing porphyrin unit into polymer is a useful way to fine-tune the photoelectric performance for efficient all-PSCs.

Carbon nanotubes are 1D nanocarbons with excellent properties and have been extensively used in various electronic and optoelectronic device applications including solar cells. Herein, we report a significant enhancement in the efficiency and stability of perovskite solar cells (PSCs) by employing single-walled carbon nanotubes (SWCNTs) in the mesoporous photoelectrode. It was found that SWCNTs provide both rapid electron transfer and advantageously shifts the conduction band minimum of the TiO2 photoelectrode and thus enhances all photovoltaic parameters of PSCs. The TiO2-SWCNTs photoelectrode based PSC device exhibited a power conversion efficiency (PCE) of up to 16.11%, while the device fabricated without SWCNTs displayed an efficiency of 13.53%. More importantly, we found that the SWCNTs in the TiO2 nanoparticles (TiO2 NPs) based photoelectrode suppress the hysteresis behavior and significantly enhance both the light and long-Term storage stability of the PSC devices. The present work provides important guidance for future investigations in utilizing carbonaceous materials for solar cells. Refereed/Peer-reviewed

To improve the performance of amorphous InGaZnOx (a-IGZO) thin film transistors (TFTs), in this thesis, Cs+ ions adsorbed IGZO (Cs-IGZO) films were prepared through a solution immersion method at low temperature. Under the modification of surface structure and oxygen vacancies concentrations of a-IGZO film, with the effective introduction of Cs+ ions into the surface of a-IGZO films, the transfer properties and stability of a-IGZO TFTs are greatly improved. Different parameters of Cs+ ion concentrations were investigated in our work. When the Cs+ ions concentration reached 2% mol/L, the optimized performance Cs-IGZO TFT was obtained, showing the carrier mobility of 18.7 cm2 V&minus, 1 s&minus, 1, the OFF current of 0.8 &times, 10&minus, 10 A, and the threshold voltage of 0.2 V, accompanied by the threshold voltage shifts of 1.3 V under positive bias stress for 5000 s.

In the past years, the conformal coating on the printed circuit board has been widely used because it offers several advantages in terms of protection and reliability of electronic circuits. However, the coating is a dielectric material, which can impact on the performance of radio-frequency components such as microstrip filters. Hence, the coating characterisation from the dielectric point of view is essential in order to design filters that meet prefixed requirements. Although the dielectric properties of commercial conformal coatings are well known, specific analyses on the effect of the coating on devices performance for space applications are not present in the literature and the coating manufactures do not often provide an appropriate characterisation of dielectric properties, making the analysis and the design of the microstrip filters difficult. The authors discuss numerical and experimental results regarding the performance of a coupled microstrip filter and show that the presence of CV-1152 coating causes a significant shift of the S-parameters. Moreover, a new configuration of the filter based on a fractal shape is proposed, which is characterised by more compact size and an optimised bandwidth.

Harnessing solar energy with solar cells based on organic materials (in particular polymeric solar cells) is an attractive alternative to silicon-based solar cells due to the advantages of lower weight, flexibility, lower manufacturing costs, easier integration with other products, low environmental impact during manufacturing and operations and short energy payback times. However, even with the latest efficiencies reported up to 17%, the reproducibility of these efficiencies is not up to par, with a significant variation in the efficiencies reported across the literature. Since these devices are based on ultrathin multilayer organic films, interfaces play a major role in their operation and performance. This review gives a concise account of the major interfacial issues that are responsible for influencing the device performance, with emphasis on their physical mechanisms. After an introduction to the basic principles of polymeric solar cells, it briefly discusses charge generation and recombination occurring at the donor-acceptor bulk heterojunction interface. It then discusses interfacial morphology for the active layer and how it affects the performance and stability of these devices. Next, the formation of injection and extraction barriers and their role in the device performance is discussed. Finally, it addresses the most common approaches to change these barriers for improving the solar cell efficiency, including the use of interface dipoles. These issues are interrelated to each other and give a clear and concise understanding of the problem of the underperformance due to interfacial phenomena occurring within the device. This review not only discusses some of the implemented approaches that have been adopted in order to address these problems, but also highlights interfacial issues that are yet to be fully understood in organic solar cells.

Organic semiconductor (OSC):polymer blends are recently increasing their popularity due to the impressive performances they offer once employed as active layer in organic field-effect transistors (OFETs). Here a novel blend formulation composed by the donor-acceptor random copolymer PDPP-TT(1)-SVS(9) and polystyrene has been processed by a solution shearing technique and employed as active material in a thin film transistor. The molecular weight of the polymer binder has revealed to be fundamental for controlling the vertical phase separation and, in turn, for determining the morphological properties of the upper surface which is critical in terms of device stability. The bi-component active layer has been tested as OFET and by using a top gate as electrolyte-gated field-effect transistor (EGOFET). Our strategy based on an OSC:polymer blend processed through a solution shearing technique has demonstrated to be efficient for improving the final device performance in ambient conditions., F.L. and Q.Z. contributed equally to this work. F.L., Q.Z. and M.M.-T. thank the ERC-StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) project, FANCY CTQ2016-80030-R, the Generalitat de Catalunya (2017-SGR-918), and the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Program for Centres of Excellence in R&D (SEV-2015-0496). Q.Z. acknowledges the China Scholarship Council, the National Natural Science Foundation of China (NSF) (Grant No. 11404266). Q.Z. was enrolled in the Materials Science Ph.D. Program of Universitat Autònoma de Barcelona. F.L. gratefully acknowledges the “Juan de la Cierva” program. Y.-H. K. Thanks the National Research Foundation of Korea (NRF) funded by the Ministry of Science (NRF-2018R1A2A1A05078734).

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted significant attention in recent years due to their high-power conversion efficiency, simple fabrication, and low material cost. However, due to their high sensitivity to moisture and oxygen, high efficiency PSCs are mainly constructed in an inert environment. This has led to significant concerns associated with the long-term stability and manufacturing costs, which are some of the major limitations for the commercialization of this cutting-edge technology. Over the past few years, excellent progress in fabricating PSCs in ambient conditions has been made. These advancements have drawn considerable research interest in the photovoltaic community and shown great promise for the successful commercialization of efficient and stable PSCs. In this review, after providing an overview to the influence of an ambient fabrication environment on perovskite films, recent advances in fabricating efficient and stable PSCs in ambient conditions are discussed. Along with discussing the underlying challenges and limitations, the most appropriate strategies to fabricate efficient PSCs under ambient conditions are summarized along with multiple roadmaps to assist in the future development of this technology.

All-polymer solar cells (APSCs), composed of semiconducting donor and acceptor polymers, have attracted considerable attention due to their unique advantages compared to polymer-fullerene-based devices in terms of enhanced light absorption and morphological stability. To improve the performance of APSCs, the morphology of the active layer must be optimized. By employing a random copolymerization strategy to control the regularity of the backbone of the donor polymers (PTAZ-TPDx) and acceptor polymers (PNDI-Tx) the morphology can be systematically optimized by tuning the polymer packing and crystallinity. To minimize effects of molecular weight, both donor and acceptor polymers have number-average molecular weights in narrow ranges. Experimental and coarse-grained modeling results disclose that systematic backbone engineering greatly affects the polymer crystallinity and ultimately the phase separation and morphology of the all-polymer blends. Decreasing the backbone regularity of either the donor or the acceptor polymer reduces the local crystallinity of the individual phase in blend films, affording reduced short-circuit current densities and fill factors. This two-dimensional crystallinity optimization strategy locates a PCE maximum at highest crystallinity for both donor and acceptor polymers. Overall, this study demonstrates that proper control of both donor and acceptor polymer crystallinity simultaneously is essential to optimize APSC performance.

Efficiencies of organic photovoltaic (OPV) devices have been steadily climbing, but there is still a prominent gap in understanding the relationship between fabrication and performance. Side chain substitution is one processing parameter that can change OPV device efficiency considerably, primarily because of variations in morphology. In this work, we explain the morphological link between side chain selection and device performance in one polymer to aid in the development of design rules more broadly. We study the morphology of an OPV active layer using a PBDTTPD-backbone polymer with four different side chain configurations, which are shown to change device efficiency by up to 4 times. The optimal device has the smallest domain sizes, the highest degree of crystallinity, and the most face-on character. This is achieved with two branched 2-ethylhexyl (2EH) side chains placed symmetrically on the BDT unit and a linear octyl (C8) side chain on the TPD unit. Substituting either side chain (C14 on BDT and/or 2EH on TPD) makes the orientation less face-on, while the TPD side chain primarily affects domain size. For all side chains, the addition of fullerene increases polymer crystallization compared to the neat film, but the degree of mixing between polymer and fullerene varies with side chain. Interestingly, the optimal device has a negligible amount of mixed phase. The domain sizes present in the optimal system are remarkably unchanged with a changing fullerene ratio between 10 and 90%, hinting that the polymer preferentially self-assembles into 10-20 nm crystallites regardless of concentration. The formation of this crystallite may be the key factor inhibiting mixed phase.

In the periodic table of elements, boron (B, atomic number, 5) and nitrogen (N, atomic number, 7) are neighboring to the carbon (C, atomic number, 6). Thus, the total electronic number of two carbons (12) is equal to the electronic sum of one boron (5) and one nitrogen (7). Accordingly, replacing two carbons with one boron and one nitrogen in a π-conjugated structure gives an isoelectronic system, i.e., the BN perturbed π-conjugated system, comparing to their all-carbon analogs. The BN embedded π-conjugated systems have unique properties, e.g., optical absorption, emission, energy levels, bandgaps, and packing order in contrast to their all-carbon analogs and have been intensively studied in terms of novel synthesis, photophysical characterizations, and electronic applications in recent years. In this review, we try to summarize the synthesis methods, optoelectronic properties, and progress in organic photovoltaic (OPV) applications of the representative BN embedded polycyclic π-conjugated systems. Firstly, the narrative will be commenced with a general introduction to the BN units, i.e., B←N coordination bond, B-N covalent bond, and N-B←N group. Then, the representative synthesis strategies toward π-conjugated systems containing B←N coordination bond, B-N covalent bond, and N-B←N group will be summarized. Afterwards, the frontier orbital energy levels, optical absorption, packing order in solid state, charge transportation ability, and photovoltaic performances of typical BN embedded π-conjugated systems will be discussed. Finally, a prospect will be proposed on the OPV materials of BN doped π-conjugated systems, especially their potential applications to the small molecules organic solar cells.

International audience; The synthesis, structural and optoelectronic characterization of a family of sterically congested cyclometalated cationic Ir(iii) complexes of the form [Ir(C^N)2(dtBubpy)]PF6 (with dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine and C^N = a cyclometalating ligand decorated at the 4-position of the pyridine ring and/or the 3-position of the phenyl ring with a range of sterically bulky substituents) are reported. This family of complexes is compared to the unsubstituted analogue complex R1 bearing 2-phenylpyridinato as cyclometalating ligand. The impact of sterically bulky substituents on the C^N ligands on both the solid state photophysics and light-emitting electrochemical cell (LEEC) device performance is investigated. X-ray diffraction analysis of complexes 1a, R2, 2a, and 1b show an increasing internuclear distance in the solid state, within these four complexes. Emission studies in solution and neat film show that the chosen substituents essentially do not impact the emission energy. The photoluminescence quantum yields (ΦPL) are in the same range (ΦPL ∼ 25-31%), except for 1b, which shows a lower ΦPL of 12%. All complexes exhibit similar monoexponential emission lifetimes in the submicrosecond regime. LEECs based on R1, 1a, 1b and R2 were fabricated, showing yellow luminescence and moderate efficiencies and lifetimes. The arguably best performing LEEC device, showing the highest luminance (737 cd m-2), current efficiency (7.4 cd A-1) and EQE (2.6%), employed emitter 1a.

All-solution processed organic solar cells with inverted device architecture were demonstrated. Devices contain opaque bottom electrodes and semitransparent top electrodes, resulting in top illuminated devices. Nanoparticles-based Ag ink was used for inkjet printing both top and bottom electrodes. Semi-transparent top electrode consists of high conductivity PEDOT:PSS and Ag current collecting grids. Printed electrodes were compared to evaporated Ag electrodes (both top and bottom) and to ITO electrode in terms of transmittance, roughness, sheet resistance and device performance. All-solution processed devices with top illumination have average PCE of 2.4%, using P3HT:PCBM as photoactive layer. Top-illuminated devices with inverted architecture and bottom-illuminated device with conventional architecture, containing the identical layers, but in the reverse sequence, were then compared. Performed studies have revealed an advantage of inverted cell architecture. cop. 2015 Elsevier B.V. All rights reserved.

Understanding of structural, optical, and electrical properties of thin films are very important for a reliable device performance. In the present work, the effect of postdeposition annealing on stoichiometric SrTiO3 (STO) thin films grown by radio frequency magnetron sputtering at room temperature on p-type Si (100) and quartz substrates were studied. Highly transparent and well adhered thin films were obtained in visible and near infrared regions. As-deposited films were amorphous, while nanocrystalline and polycrystalline phases of the STO thin films formed as a function of annealing temperature. Films annealed at 300 degrees C showed nanocrystallinity with some amorphous phase. Crystallization started after 15 min annealing at 700 degrees C, and further improved for films annealed at 800 degrees C. However, crystallinity reduced for films which were annealed at 900 degrees C. The optical and electrical properties of STO thin films affected by postdeposition annealing at 800 degrees C: E-g values decreased from 4.50 to 4.18 eV, n(lambda) values (at 550 nm) increased from 1.81 to 2.16. The surface roughness increased with the annealing temperature due to the increased crystallite size, densification and following void formation which can be seen from the scanning electron microscopy images. The highest dielectric constants (46 at 100 kHz) observed for films annealed at 800 degrees C; however, it was lower for 300 degrees C annealed (25 at 100 kHz) and as-deposited (7 at 100 kHz) STO films having similar to 80 nm thickness. (C) 2017 American Vacuum Society.

A series of donor-acceptor-donor (D-A-D) structured small-molecule compounds, with 3,3'-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) as a novel electron acceptor building block coupled with various electron donor end-capping moieties (thiophene, bithiophene and benzofuran), were synthesized and characterized. When the fused-ring benzofuran is combined to EBI (EBI-BF), the molecules displayed a perfectly planar conformation and afforded the best charge tranport properties among these EBI compounds with a hole mobility of up to 0.021 cm2 V-1 s-1. All EBI-based small molecules were used as donor material along with a PC61BM acceptor for the fabrication of solution-processed bulk-heterojunction (BHJ) solar cells. The best performing photovoltaic devices are based on the EBI derivative using the bithiophene end-capping moiety (EBI-2T) with a maximum power conversion efficiency (PCE) of 1.92%, owing to the broad absorption spectra of EBI-2T and the appropriate morphology of the BHJ. With the aim of establishing a correlation between the molecular structure and the thin film morphology, differential scanning calorimetry, atomic force microscopy and X-ray diffraction analysis were performed on neat and blend films of each material.

In this paper, a detailed 3-D numerical analysis is carried out to study and evaluate CMOS logic device and circuit performance of gate-all-around (GAA) Si nanowire (NW) field-effect transistors (FETs) operating in sub-22-nm CMOS technologies. Employing a coupled drift-diffusion room temperature carrier transport formulation, with 2-D quantum confinement effects, we numerically simulate Si GAA NWFET electrical characteristics. The simulation predictions, on the device performance, short channel effects, and their dependence on NW geometry scaling, are in good agreement with the Si NWFET experimental data reported in literature. Superior electrostatic integrity, OFF-state device performance, lower circuit delays, and faster switching in the Si GAA NWFET-based CMOS circuits are numerically demonstrated in comparison with an Si-on-insulator FinFET. The mixed-mode numerical simulations also predict low supply voltage operations for the Si NWFET-based logic circuits.

Carbon nanotubes are shown to be beneficial additives to perovskite solar cells, and the inclusion of such nanomaterials will continue to play a crucial role in the push toward developing efficient and stable device architectures. Herein, titanium dioxide/carbon nanotube composite perovskite solar cells are fabricated, and device performance parameters are correlated with spectroscopic signatures of the materials to understand the origin of performance enhancement. By probing the charge carrier dynamics with photoluminescence and femtosecond transient absorption spectroscopy, the results indicate that charge transfer is not improved by the presence of the carbon nanotubes. Instead, carbon nanotubes are shown to passivate the electronic defect states within the titanium dioxide, which can lead to stronger radiative recombination in the titanium dioxide/carbon nanotube films. The defect passivation allows the perovskite solar cells made using an optimized titanium dioxide/carbon nanotube composite to achieve a peak power conversion efficiency of 20.4% (19% stabilized), which is one of the highest values reported for perovskite solar cells not incorporating a mixed cation light absorbing layer. The results discuss new fundamental understandings for the role of carbon nanomaterials in perovskite solar cells and present a significant step forward in advancing the field of high‐performance photovoltaics.

SWCNT network morphology and TFT performance of polyfluorene wrapped sc-SWCNT on different substrates is reported. The polymer/tube weight ratio and concentration impacts network formation and device performance. Hydrophilic SiO2 surfaces show stronger adsorption compared to poly-l-lysine treated SiO2, which leads to more uniform and higher density networks. TFTs with mobility up to 38 cm2/Vs with

In this paper, the effect of angstrom-thick atomic layer deposited (ALD) ZnO embedded layer on photovoltaic (PV) performance of Nanowire-Based All-TiO2 solar cells has been systematically investigated. Our results indicate that by varying the thickness of ZnO layer the efficiency of the solar cell can be significantly changed. It is shown that the efficiency has its maximum for optimal thickness of 1 ALD cycle in which this ultrathin ZnO layer improves device performance through passivation of surface traps without hampering injection efficiency of photogenerated electrons. The mechanisms contributing to this unprecedented change in PV performance of the cell have been scrutinized and discussed. (C) 2015 Elsevier Ltd. All rights reserved.

In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase-separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. (c) 2015 Wiley Periodicals, Inc. Funding Agencies|European Communitys Seventh Framework Programme under MOMA project [248092]

The authors demonstrate improved device performance of GaN metal-semiconductor-metal ultraviolet (UV) photodetectors (PDs) by ultrathin HfO2 (UT-HfO2) layer on GaN. The UT-HfO2 interfacial layer is grown by atomic layer deposition. The dark current of the PDs with UT-HfO2 is significantly reduced by more than two orders of magnitude compared to those without HfO2 insertion. The photoresponsivity at 360 nm is as high as 1.42 A/W biased at 5 V. An excellent improvement in the performance of the devices is ascribed to allowed electron injection through UT-HfO2 on GaN interface under UV illumination, resulting in the photocurrent gain with fast response time. (C) 2015 American Vacuum Society.

High-resolution compact-size focal plane arrays (FPAs) suffer the fundamental geometrical tradeoff between the optical resolution (pixel size miniaturization) and the optical crosstalk (spillover of neighboring pixel focusing). For FPAs, our previously reported metallic metasurfaces reached an unprecedented level of crosstalk suppression. However, practical utilization of these metallic microlens arrays has proved to be intrinsically limited due to the low device efficiency (of the order of 0.10) resulting from the fundamental absorption losses of metals and their cross-polarization scheme. Exceeding this limit, here we show highly efficient microlens designs enabled by dielectric metasurfaces for mid-wave infrared (MWIR) operation. These dielectric MWIR FPAs allow for a substantially high device efficiency over 0.80 without compromising the optical crosstalk performance. Systematically studying dielectric nanoantennas of silicon nanodisks that do not dictate the cross-polarization scheme using full-wave solutions, we found that the optical crosstalk is suppressed to low levels ≤≤ 3.0% while sustaining the high efficiency. A figure-of-merit (FoM) defined for the device performance as the focusing efficiency per optical crosstalk times the f-number achieves 84, which is superior to all other types of MWIR FPAs reported to date, all falling below a maximum FoM of 70. These findings indicate that the proposed approach can pave the way for the practical usage of metasurface microlens arrays in MWIR. Published version

In this paper, the design and experimental characterization of a tunable microstrip bandpass filter based on liquid crystal technology are presented. A reshaped microstrip dual-mode filter structure has been used in order to improve the device performance. Specifically, the aim is to increase the pass-band return loss of the filter by narrowing the filter bandwidth. Simulations confirm the improvement of using this new structure, achieving a pass-band return loss increase of 1.5 dB at least. Because of the anisotropic properties of LC molecules, a filter central frequency shift from 4.688 GHz to 5.045 GHz, which means a relative tuning range of 7.3%, is measured when an external AC voltage from 0 Vrms to 15 Vrms is applied to the device. © 2014 by the authors. Authors acknowledge Grupo de Fotónica Aplicada (Universidad Politécnica de Madrid, Spain) for the use of their facilities for the manufacture of the device. Authors thank funding support from the Spanish Ministerio de Economía y Competitividad (grant No. TEC2009-13991-C02-01) and Comunidad de Madrid (grant No. FACTOTEM2 S2009/ESP/1781).

The presence of oxygen in silicon single crystals causes the formation of several defects which can make the properties of silicon vary, with a strong influence also on the microelectronic devices subsequently fabricated on the wafers. A brief review of the phenomena connected to oxygen in silicon is presented here, with particular attention to the different effects of interstitial and precipitated oxygen on the silicon properties and to the use of the most widely used physical techniques for their study

Date of Conference: 8-12 Sept. 2013 We fabricated an ZnO based thin-film photo-transistor with electrically tunable photo-responsivity operating in the UV and visible spectra and designed plasmonic structures enhancing the device performance up to 6 folds below the band-gap of ZnO. © 2013 IEEE.

Effect of transverse quantization on the broken vs. staggered band lineup of InAs/Al(x)Ga(1-x)Sb TFETs is investigated, showing that cross-sections up to 10nm lead to staggered configurations for any value of the Al mole fraction x. Device performance is optimized as a function of cross-sectional size, Al content and possible source/channel underlap, while ensuring low standby power (LSTP) or low operating power (LOP) compatible off-current levels. Guidelines are provided and an “optimal” design is proposed which provides a minimum sub-threshold slope (SS) of 7.2 mV/dec along with a maximum on-state current (Ion) of 175μA/μm.

Five new polymers based on the 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene core (BODIPY) chromophore moiety have been synthesized as low bandgap polymers for optoelectronic applications. The polymers exhibited high solubility in common organic solvents and optical bandgaps ranging from 1.7-2 eV. The materials were characterized using NMR, UV-Vis, steady state and time-resolved photoluminescence and the energy levels were examined using electrochemistry and validated using quantum chemical calculations. Finally, a representative BODIPY derivative : PCBM blend was examined in terms of photovoltaic properties. Preliminary device performance parameters as a function of photo-active layer thickness and composition are reported and discussed, relating to power conversion efficiency values. © The Royal Society of Chemistry 2013. 3 26 10221 10229

In this work we investigate the achievable device performance of steep-slope nanowire FETs based on the filtering of the high-energy electrons via a superlattice heterostructure in the source extension. Four material pairs are investigated for the superlattice (SL), with the aim to identify the most promising ones with respect to the typical FET evaluation metrics. We found that the InGaAs-InAlAs pair can provide an inverse subthreshold slope SS = 13 mV/dec and an on-state current ION = 4.5 mA/μm@VDD = 0.4V. These results outperform the ITRS requirements for the 21 nm technology node.

In this work, we present a platform for testing the device performance of a cavity-emitter system, using an ensemble of emitters and a tapered optical fiber. This method provides high-contrast spectra of the cavity modes, selective detection of emitters coupled to the cavity and an estimate of the device performance in the single-emitter case. Using nitrogen-vacancy (NV) centers in diamond and a GaP optical microcavity, we are able to tune the cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a tapered fiber and measure the fiber-coupled NV spontaneous emission decay. Theoretically, we show that the fiber-coupled average Purcell factor is 2-3 times greater than that of free-space collection, although due to ensemble averaging it is still a factor of 3 less than the Purcell factor of a single, ideally placed center. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Graphical abstract Electric chatacterization of organic field effect transistors with PVT dielectric layer: Pentacene is used as active layer in p-channel device; Fullerene is the active layer in n-channel device. Channel length is 2mm, channel width is 0.06mm. Research highlights ► PVT shows low leakage current and high breakdown voltage. ► Both n-channel and p-channel OFET devices give low threshold voltage and are lack of hysteresis. ► Excellent film formation property of PVT allows for fabricating low voltage operation OFET devices. ► All solution processed polymer ambipolar OFET device is realized via layer by layer coating., Water soluble poly(1-vinyl-1,2,4-triazole) (PVT) as a novel dielectric layer for organic field effect transistor is studied. Dielectric spectroscopy characterization reveals it has low leakage current and rather high breakdown voltage. Both n-channel and p-channel organic field effect transistors are fabricated using pentacene and fullerene as active layers. Both devices show device performances with lack of hysteresis, very low threshold voltages and high on/off ratios. Excellent film formation property is utilized to make AlOx and thin PVT bilayer in order to decrease the operating voltage of the devices. All solution processed ambipolar device is fabricated with simple spin coating steps using poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH–PPV) end capped with polyhedral oligomeric silsesquioxanes (POSS) as active layer. Our investigations show that PVT can be a very promising dielectric for organic field effect transistors.

LiNbO3 is a crystal widely used in photonics and acoustics, for example in electro-optic modulation, nonlinear optical frequency conversion, electric field sensing and surface acoustic wave filtering. It often needs to be combined with other materials and used in thin layers to achieve the adequate device performance. In this paper, we investigate direct bonding of LiNbO3 crystals with other dielectric materials, such as Si and fused silica (SiO2), and we show that specific surface chemical cleaning, together with Ar or O2 plasma activation, can be used to increase the surface free energy and achieve effective bonding at room temperature. The resulting hybrid material bonding is very strong, making the dicing and grinding of LiNbO3 layers as thin as 15 µm possible. To demonstrate the application potentials of the proposed bonding technique, we have fabricated and characterized a high-voltage field sensor with high sensitivity in a domain inverted and bonded LiNbO3 waveguide substrate.

Incremental increase in dimethyl sulfoxide (or dimethyl formamide) in ortho-dichlorobenzene solution of poly [N -heptadecanyl-2,7-carbazole-alt-5,5- (4′, 7′ -di-2-thienyl- 2′, 1′, 3′ -benzothiadiazole)] (PCDTBT) gradually reduces the polymer-solvent interaction, the attraction forces between polymer chains become more dominant, and the polymer chains adopt a tight and contracted conformation with more interchain interactions, resulting in a progressive aggregation in both solutions and films. This was used to fine tune the morphology of PCDTBT/ PC71 BM based solar cells, leading to improved domain structure and hole mobility in the active layer, and significantly improved photovoltaic performance. The power conversion efficiency increased from 6.0% to 7.1% on devices with an active area of 1.0 cm2. © 2011 Crown.

Bistable two-section Fabry-Perot lasers with a saturable absorber have been fabricated, comprehensively characterized, and optimized with respect to gain and optical switching contrast. Best device performance requires the individual optimization of both section lengths, and a proper choice of current conditions. Light has to be injected into the gain section, instead of the absorber section, to take full advantage of device qualities. Based on this optimization high, all optical switching gain (26 dB) and large contrast (18 dB) have been achieved simultaneously. >

Strain engineering is used to maintain Moore's Law in scaled CMOS devices and as a technology booster for More-than-Moore devices in the nanoelectronics era. Strain is crucial because of its ability to increase electron and hole mobilities in Si. However, accurate correlations between electrical performance and strain measurements are needed to enable the necessary feedback between materials, processing and devices to achieve best possible solutions. In this work, we outline new methods for sensitive 3D profiling of strain on a nanoscale. High-resolution vertical and lateral strain profiles applicable to both global (biaxial) and process-induced (uniaxial) strained Si devices are demonstrated. Raman spectroscopy is pushed to its present limit for precise analysis of strain in small geometry devices, including the use of tip-enhanced Raman spectroscopy (TERS) to improve the spatial resolution further. TERS maps are compared with atomic force microscopy data collected simultaneously and show that variations in surface morphology correlate directly with strain in the epitaxial layers. Sub-nm strain profiling is applied to strained Si and SiGe MOSFET channels. Strain is profiled across patterned uniaxial strained-Si-on-insulator structures and analysed in bended nanowire transistors. Finally strain is investigated across the channel regions of electrically measured SiGe p-MOSFETs. Good agreement between nanoscale strain measurements and finite element modelling is demonstrated. Sample preparation is included in the analysis and genuine effects of processing are investigated. (C) 2009 Elsevier Ltd. All rights reserved.