New Family of Ruthenium‐Dye‐ Sensitized Nanocrystalline TiO2 Solar Cells with a High Solar‐Energy‐Conversion Efficiency

A new type of ruthenium complexes 6 – 8 with tridentate bipyridine–pyrazolate ancillary ligands has been synthesized in an attempt to elongate the π‐conjugated system as well as to increase the optical extinction coefficient, possible dye uptake on TiO₂, and photostability. Structural characterization, photophysical studies, and corresponding theoretical approaches have been made to ensure their fundamental basis. As for dye‐sensitized solar cell applications, it was found that 6 – 8 possess a larger dye uptake of 2.4 × 10^–7 mol cm^–2, 1.5 × 10^–7 mol cm^–2, and 1.3 × 10^–7 mol cm^–2, respectively, on TiO₂ than that of the commercial N3 dye (1.1 × 10^–7 mol cm^–2). Compound 8 works as a highly efficient photosensitizer for the dye‐sensitized nanocrystalline TiO₂ solar cell, producing a 5.65 % solar‐light‐to‐electricity conversion efficiency (compare with 6.01 % for N3 in this study), a short‐circuit current density of 15.6 mA cm^–2, an open‐circuit photovoltage of 0.64 V, and a fill factor of 0.57 under standard AM 1.5 irradiation (100 mW cm^–2). These, in combination with its superior thermal and light‐soaking stability, lead to the conclusion that the concomitant tridentate binding properties offered by the bipyridine‐pyrazolate ligand render a more stable complexation, such that extended life spans of DSSCs may be expected.     

Efficient Sb2S3‐Sensitized Solar Cells Via Single‐Step Deposition of Sb2S3 Using S/Sb‐Ratio‐Controlled SbCl3‐Thiourea Complex Solution

To replace the conventional chemical bath deposition method, which is time‐consuming and has a high impurity level, a chemical single‐step deposition process employing a S/Sb ratio‐controlled SbCl₃‐thiourea complex solution is introduced to load Sb₂S₃ into a mesoporous TiO₂ electrode. This technique enables the fabrication of efficient and reproducible Sb₂S₃‐sensitzed inorganic–organic heterojunction hybrid solar cells with hole‐conducting conjugated polymers. The most efficient cell exhibits a short‐circuit current density of 16.1 mA cm^?2, an open circuit voltage of 595.5 mV, and a fill factor of 66.5%, yielding a power conversion efficiency of ≈6.4% at standard AM1.5G condition (100 mW cm^?2).     

π‐Conjugated Oligothiophene‐Based Polycatenar Liquid Crystals: Self‐Organization and Photoconductive,Luminescent, and Redox Properties

A series of liquid‐crystalline (LC) π‐ ‐conjugated oligothiophenes bearing three or two alkoxy chains at their extremities has been designed and synthesized. These polycatenar oligothiophenes form various LC nanostructures including smectic, columnar, and micellar cubic phases. These properties depend on the number and length of the terminal alkoxy chains. The hole mobilities for the oligothiophenes have been measured. The layered smectic and columnar structures are capable of transporting holes, leading to mobilities of up to 0.01 cm² V^?1 s^?1. The columnar LC assemblies have also been explored to produce linearly polarized light‐emission. Fine red polarized fluorescence is observed from a uniaxially aligned film of the oligothiophenes. The redox properties of the oligothiophenes both in solutions and in films have been examined. The oligothiophenes exhibit electrochromism upon applying an oxidative potential. The present design strategy is useful for fabricating a variety of functional electro‐active molecular assemblies.     

Polymer Solar Cells Based on a Low‐Bandgap Fluorene Copolymer and a Fullerene Derivative with Photocurrent Extended to 850 nm

Polymer solar cells have been fabricated from a recently synthesized low band‐gap alternating polyfluorene copolymer, APFO‐Green2, combined with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) from organic solutions. External quantum efficiencies (EQEs) of the solar cells show an onset at 850 nm and a peak of > 10 % located at 650 nm, which corresponds to the extended absorption spectrum of the polymer. Photocurrent of 3.0 mA cm^–2, photovoltage of 0.78 V, and power conversion efficiency of 0.9 % have been achieved in solar cells based on this new low‐bandgap polymer under the illumination of air mass 1.5 (AM 1.5) (1000 W m^–2) from a solar simulator.     

Enhanced Photocurrent Spectral Response in Low‐Bandgap Polyfluorene and C70‐Derivative‐Based Solar Cells

Plastic solar cells have been fabricated using a low‐bandgap alternating copolymer of fluorene and a donor–acceptor–donor moiety (APFO‐Green1), blended with 3′‐(3,5‐bis‐trifluoromethylphenyl)‐1′‐(4‐nitrophenyl)pyrazolino[70]fullerene (BTPF70) as electron acceptor. The polymer shows optical absorption in two wavelength ranges, λ < 500 nm and 600 < λ < 1000 nm. The BTPF70 absorbs light at λ < 700 nm. A broad photocurrent spectral response in the wavelength range 300 < λ < 1000 nm is obtained in solar cells. A photocurrent density of 3.4 mA cm^–2, open‐circuit voltage of 0.58 V, and power‐conversion efficiency of 0.7 % are achieved under illumination of AM1.5 (1000 W m^–2) from a solar simulator. Synthesis of BTPF70 is presented. Photoluminescence quenching and electrochemical studies are used to discuss photoinduced charge transfer.     

Novel Conjugated Organic Dyes for Efficient Dye‐Sensitized Solar Cells

Novel conjugated organic dyes that have N,N‐dimethylaniline (DMA) moieties as the electron donor and a cyanoacetic acid (CAA) moiety as the electron acceptor were developed for use in dye‐sensitized nanocrystalline‐TiO₂ solar cells (DSSCs). We attained a maximum solar‐energy‐to‐electricity conversion efficiency (η) of 6.8 % under AM 1.5 irradiation (100 mW cm^–2) with a DSSC based on 2‐cyano‐7,7‐bis(4‐dimethylamino‐phenyl)hepta‐2,4,6‐trienoic acid (NKX‐2569): short‐circuit photocurrent density (J_sc) = 12.9 mA cm^–2, open‐circuit voltage (V_oc) = 0.71 V, and fill factor (ff) = 0.74. The high performance of the solar cells indicated that highly efficient electron injection from the excited dyes to the conduction band of TiO₂ occurred. The experimental and calculated Fourier‐transform infrared (FT‐IR) absorption spectra clearly showed that these dyes were adsorbed on the TiO₂ surface with the carboxylate coordination form. A molecular‐orbital calculation indicated that the electron distribution moved from the DMA moiety to the CAA moiety by photoexcitation of the dye.     

The 2,2,6,6‐Tetramethyl‐1‐piperidinyloxy Radical: An Efficient,Iodine‐ Free Redox Mediator for Dye‐Sensitized Solar Cells

A promising redox system, offering an alternative to the widely used iodide/triiodide couple, based on the stable organic radical 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) has been employed in dye‐sensitized solar cells. The photovoltaic performance of this new redox couple has been evaluated by employing nanocrystalline TiO₂ films with different thickness. Judicious selections of a 5.0 μm photoanode made from TiO₂ mesoscopic particles and an organic sensitizer with a high molar extinction coefficient yield an overall solar‐to‐electric power conversion efficiency of 5.4 % under AM 1.5 illumination at 100 mW cm^–2, which is unprecedented for an iodine‐free mediator system.     

Angular‐Shaped 4,9‐Dialkyl α‐ and β‐Naphthodithiophene‐Based Donor–Acceptor Copolymers: Investigation of Isomeric Structural Effects on Molecular Properties and Performance of Field‐Effect Transistors and Photovoltaics

Two angular‐shaped 4,9‐didodecyl α‐aNDT and 4,9‐didodecyl β‐aNDT isomeric structures have been regiospecifically designed and synthesized. The distannylated α‐aNDT and β‐aNDT monomers are copolymerized with the Br‐DTNT monomer by the Stille coupling to furnish two isomeric copolymers, PαNDTDTNT and PβNDTDTNT, respectively. The geometric shape and coplanarity of the isomeric α‐aNDT and β‐aNDT segments in the polymers play a decisive role in determining their macroscopic device performance. Theoretical calculations show that PαNDTDTNT possesses more linear polymeric backbone and higher coplanarity than PβNDTDTNT. The less curved conjugated main chain facilitates stronger intermolecular π–π interactions, resulting in more redshifted absorption spectra of PαNDTDTNT in both solution and thin film compared to the PβNDTDTNT counterpart. 2D wide‐angle X‐ray diffraction analysis reveals that PαNDTDTNT has more ordered π‐stacking and lamellar stacking than PβNDTDTNT as a result of the lesser curvature of the PαNDTDTNT backbone. Consistently, PαNDTDTNT exhibits a greater field effect transistor hole mobility of 0.214 cm² V^?1 s^?1 than PβNDTDTNT with a mobility of 0.038 cm² V^?1 s^?1. More significantly, the solar cell device incorporating the PαNDTDTNT:PC₇₁BM blend delivers a superior power conversion efficiency (PCE) of 8.01% that outperforms the PβNDTDTNT:PC₇₁BM‐based device with a moderate PCE of 3.6%.     

Conjugated Molecules “Bridge”: Functional Ligand toward Highly Efficient and Long‐Term Stable Perovskite Solar Cell

Interfacial ligand passivation engineering has recently been recognized as a promising avenue, contributing simultaneously to the optoelectronic characteristics and moisture/operation tolerance of perovskite solar cells. To further achieve a win‐win situation of both performance and stability, an innovative conjugated aniline modifier (3‐phenyl‐2‐propen‐1‐amine; PPEA) is explored to moderately tailor organolead halide perovskites films. Here, the conjugated PPEA presents both “quasi‐coplanar” rigid geometrical configuration and distinct electron delocalization characteristics. After a moderate treatment, a stronger dipole capping layer can be formed at the perovskite/transporting interface to achieve favorable banding alignment, thus enlarging the built‐in potential and promoting charge extraction. Meanwhile, a conjugated cation coordinated to the surface of the perovskite grains/units can form preferably ordered overlapping, not only passivating the surface defects but also providing a fast path for charge exchange. Benefiting from this, a ≈21% efficiency of the PPEA‐modified solar cell can be obtained, accompanied by long‐term stability (maintaining 90.2% of initial power conversion efficiency after 1000 h testing, 25 °C, and 40 ± 10 humidity). This innovative conjugated molecule “bridge” can also perform on a larger scale, with a performance of 18.43% at an area of 1.96 cm².     

Effect of Oligothienyl Chain Length on Tuning the Solar Cell Performance in Fluorene‐Based Polyplatinynes

A series of solution‐processable and strongly visible‐light absorbing polyplatinynes containing oligothienyl–fluorene ring hybrids were synthesized and characterized. These rigid‐rod organometallic materials are soluble in polar organic solvents and show intense absorptions in the visible spectral region, rendering them excellent candidates for bulk heterojunction polymer solar cells. The photovoltaic behavior depends significantly on the number of thienyl rings along the polymer chain, and some of these polymer solar cells show high power conversion efficiencies (PCEs) of up to 2.9% and a peak external quantum efficiency to 83% under AM1.5 simulated solar illumination. The effect of oligothienyl chain length on improving the polymer solar cell efficiency and on their optical and charge transport properties is elucidated in detail. At the same blend ratio of 1:5, the light‐harvesting capability and PCE increase markedly with increasing number of thienyl rings. The power dependencies of the solar cell parameters (including the short‐circuit current density, open‐circuit voltage, fill‐factor, and PCE) were also examined. The present work opens up an attractive avenue to developing conjugated metallopolymers with broad and strong solar energy absorptions and tunable solar cell efficiency and supports the potential of metalated conjugated polymers for efficient power generation.     

Multibranched Octupolar Module Embedded Covalent Organic Frameworks Enable Efficient Two‐Photon Fluorescence

Covalent organic frameworks (COFs) have emerged as potential light emitting polymers for optoelectronic and optical devices, but their nonlinear optical properties, particularly two‐photon absorption and fluorescence (TPA/TPF), have seldom been explored. Herein, to construct octupolar three‐branched modules (e.g., acceptor 3‐(donor‐core), triphenylbenzene core) within a 2D cyano‐sp²c‐conjugated framework is proposed that results in two‐photon luminescent COFs, combining a large TPA cross section and high quantum yield (QY). Such octupolar module‐embedded sp²c‐conjugated COFs emit not only intense one‐photon fluorescence with QY of 27.2% in the solid state and 38.1% in tetrahydrofuran—superior to almost all reported COFs, but also efficient two‐photon fluorescence with large TPA cross section of 1225 GM—remarkably surpassing the corresponding cyano‐sp²c‐linked model compounds (104 GM). The finding highlights the synergy between sp²c‐conjugated framework and octupolar modules that leads to markedly improved TPA response owing to extended conjugated length, enhanced planarity and multidimensional intramolecular interaction. In view of the versatility of the branched chromophore, the proposed design idea is expected to be used to exploit more two‐photon active COF materials for a range of applications. Multiple uses of the COF in information encryption and warm white light‐emitting diodes are also exemplified.     

Synthesis of 2,7‐Carbazolenevinylene‐Based Copolymers and Characterization of Their Photovoltaic Properties

New electroactive and photoactive conjugated copolymers consisting of alternating 2,7‐carbazole and oligothiophene moieties linked by vinylene groups have been developed. Different oligothiophene units have been introduced to study the relationship between the polymer structure and the electronic properties. The resulting copolymers are characterized by UV‐vis spectroscopy, size‐exclusion chromatography, and thermal and electrochemical analyses. Bulk heterojunction photovoltaic cells from different copolymers and a soluble fullerene derivative, [6,6]‐phenyl‐C₆₁ butyric acid methyl ester, have been fabricated, and promising preliminary results are obtained. For instance, non‐optimized devices using poly(N‐(4‐octyloxyphenyl)‐2,7‐carbazolenevinylene‐alt‐3″,4″‐dihexyl‐2,2′;5′,2″;5″,2″′;5″′,2″″‐quinquethiophenevinylene 1″,1″‐dioxide) as an absorbing and hole‐carrier semiconductor exhibit power conversion efficiency up to 0.8 % under air mass (AM) 1.5 illumination. These features make 2,7‐carbazolenevinylene‐based and related polymers attractive candidates for solar‐cell applications.     

Thin‐film (25.5 μm) solar cells from layer transfer using porous silicon with 32.7 mA/cm2 short‐circuit current density

We fabricate a 25.5‐μm‐thick monocrystalline Si solar cell with a confirmed power conversion efficiency of 15.4% and an area of 3.88 cm² using a layer transfer process with porous Si. The process is free of photolithography and contains no high‐temperature oxidation steps. We investigate three design features that improve the short‐circuit current density to a value of 32.7 mA/cm² under AM1.5 illumination. The detached back reflector contributes 2 mA/cm², a reduced front‐surface reflectance accounts for an additional 2 mA/cm² and a reduced base doping increases the current density by 1 mA/cm². Copyright © 2002 John Wiley & Sons, Ltd.     

Highly efficient dye‐sensitized solar cells using phenothiazine derivative organic dyes

Two novel organic dyes have been synthesized using electron rich phenothiazine as electron donors and oligothiophene vinylene as conjugation spacers. The two dyes (2E)‐2‐cyano‐3‐(5‐(5‐((E)‐2‐(10‐(2‐ethylhexyl)‐10H‐phenothiazin‐7‐yl)vinyl)thiophen‐2‐yl)thiophen‐2‐yl)acrylic acid (PTZ‐1) and (2E)‐3‐(5‐(5‐(4,5‐bis((E)‐2‐(10‐(2‐ethylhexyl)‐10H‐phenothiazin‐3‐yl)vinyl)thiophen‐2‐yl)thiophen‐2‐yl)thiophen‐2‐yl)‐2‐cyanoacrylic acid (PTZ‐2) were fully characterized and employed in dye‐sensitized solar cells (DSCs) to explore the effect of disubstituted donors on photovoltaic (PV) performance. The solar cells sensitized by the PTZ1 dye have a high IPCE plateau of 80% and achieve a short‐circuit photocurrent density of 12.98 mA/cm², an open‐circuit voltage of 0.713 V, and a fill factor (ff) of 66.6%, corresponding to a conversion efficiency of 6.17% under AM 1.5 100 mW/cm² illumination. The different performance of the solar cells based on the two dyes can be understood from the studies of the electron kinetics by electrochemical impedance spectroscopy (EIS). These investigations reveal that disubstituted donors in the organic sensitizers of three or more conjugation units deteriorate the PV performance due to enhanced recombination. Copyright © 2010 John Wiley & Sons, Ltd.     

Thieno[3,2‐b]thiophene‐diketopyrrolopyrrole Containing Polymers for Inverted Solar Cells Devices with High Short Circuit Currents

The synthesis and characterization four diketopyrrolopyrrole containing conjugated polymers for use in organic photovoltaics is presented. Excellent energy level control is demonstrated through heteroatomic substitution whilst maintaining similar solid state properties as shown by X‐ray diffraction and atomic force microscopy. Inverted solar cells were fabricated with the best devices having short circuit currents exceeding 16 mA cm^?2 and efficiencies of over 5% irrespective of whether [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₀BM) or [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₀BM) is used. Transient absorption spectroscopy on the bulk heterojunction blends shows efficient charge photo‐generation, with the variations in short circuit current correlated to the energetic offset between polymer and fullerene.     

Short‐circuit current of solar cells under artificial light

A model to estimate the short‐circuit current of a solar cell under artificial light from the short‐circuit current of the same solar cell under AM1.5 1 kW/m² is described. The results may help designers of solar‐powered portable equipment and consumer products working indoors or under a mixture of artificial and sunlight. It is concluded that the ratio of the short‐circuit currents of the same solar cell generated under fluorescent light of 1 lux illuminance divided by the short‐circuit current generated under standard 1 Sun AM1.5 conditions is around 3 × 10⁻⁶ for typical crystalline silicon and CIS solar cells. This value is one order of magnitude greater if the light source considered is an incandescent lamp. In the case of amorphous silicon solar cells the value of the ratio is close to 8 × 10⁻⁶ either for fluorescent or incandescent lamps. CdTe solar cells are also considered, and this factor is about 4 × 10⁻⁶ under fluorescent light, and four times bigger when an incandescent lamp is used. Some measurements performed validate the figures obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

A Thiophene‐Based Anchoring Ligand and Its Heteroleptic Ru(II)‐Complex for Efficient Thin‐Film Dye‐Sensitized Solar Cells

A novel heteroleptic Ru^II complex (BTC‐2) employing 5,5′‐(2,2′‐bipyridine‐4,4′‐diyl)‐bis(thiophene‐2‐carboxylic acid) (BTC) as the anchoring group and 4,4′‐ dinonyl‐2,2′‐bipiridyl and two thiocyanates as ligands is prepared. The photovoltaic performance and device stability achieved with this sensitizer are compared to those of the Z‐907 dye, which lacks the thiophene moieties. For thin mesoporous TiO₂ films, the devices with BTC‐2 achieve higher power conversion efficiencies than those of Z‐907 but with a double‐layer thicker film the device performance is similar. Using a volatile electrolyte and a double layer 7 + 5 μm mesoporous TiO₂ film, BTC‐2 achieves a solar‐to‐electricity conversion efficiency of 9.1% under standard global AM 1.5 sunlight. Using this sensitizer in combination with a low volatile electrolyte, a photovoltaic efficiency of 8.3% is obtained under standard global AM 1.5 sunlight. These devices show excellent stability when subjected to light soaking at 60 °C for 1000 h. Electrochemical impedance spectroscopy and transient photovoltage decay measurements are performed to help understand the changes in the photovoltaic parameters during the aging process. In solid state dye‐sensitized solar cells (DSSCs) using an organic hole‐transporting material (spiro‐MeOTAD, 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene), the BTC‐2 sensitizer exhibits an overall power conversion efficiency of 3.6% under AM 1.5 solar (100 mW cm^?2) irradiation.     

Recently Advanced Polymer Materials Containing Dithieno[3,2‐b:2′,3′‐d]phosphole Oxide for Efficient Charge Transfer in High‐Performance Solar Cells

Two novel semiconducting polymers based on benzodithiophene and dithienophosphole oxide (DTP) units are designed and synthesized. A novel electron‐deficient DTP moiety is developed. Surprisingly, the introduction of DTP units brings highly polarizable characteristics, which is beneficial for the photocurrent in solar cells. Thus, the donor–acceptor type of conjugated polymers based on this novel acceptor has superior charge transfer properties and highly efficient PL quenching efficiencies. As a result, polymer solar cells (PSCs) with high power conversion efficiencies of 6.10% and 7.08% are obtained from poly(3,5‐didodecyl‐4‐phenylphospholo[3,2‐b:4,5‐b']dithiophene–4‐oxide‐alt‐4,8‐bis(5‐decylthiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTT) and PDTP–4‐oxide‐alt‐4,8‐bis(5‐decylselenophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTSe), respectively, when the photoactive layer is processed with the 1,8‐octanedithiol (ODT) additive. The PDTP–BDTSe copolymer is now the best performing DTP‐based material for PSCs. Using the polarizable unit strategy determined in this study for the molecular design of conjugated polymers is expected to greatly advance the development of organic electronic devices.     

Donor and Acceptor Unit Sequences Influence Material Performance in Benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐Difluoroquinoxaline Small Molecule Donors for BHJ Solar Cells

Well‐defined small molecule (SM) donors can be used as alternatives to π‐conjugated polymers in bulk‐heterojunction (BHJ) solar cells with fullerene acceptors (e.g., PC₆₁/₇₁BM). Taking advantage of their synthetic tunability, combinations of various donor and acceptor motifs can lead to a wide range of optical, electronic, and self‐assembling properties that, in turn, may impact material performance in BHJ solar cells. In this report, it is shown that changing the sequence of donor and acceptor units along the π‐extended backbone of benzo[1,2‐b:4,5‐b′]dithiophene–6,7‐difluoroquinoxaline SM donors critically impacts (i) molecular packing, (ii) propensity to order and preferential aggregate orientations in thin‐films, and (iii) charge transport in BHJ solar cells. In these systems ( SM1‐3 ), it is found that 6,7‐difluoroquinoxaline ([2F]Q) motifs directly appended to the central benzo[1,2‐b:4,5‐b′]dithiophene (BDT) unit yield a lower‐bandgap analogue ( SM1 ) with favorable molecular packing and aggregation patterns in thin films, and optimized BHJ solar cell efficiencies of ≈6.6%. ¹H‐¹H DQ‐SQ NMR analyses indicate that SM1 and its counterpart with [2F]Q motifs substituted as end‐group SM3 possess distinct self‐assembly patterns, correlating with the significant charge transport and BHJ device efficiency differences observed for the two analogous SM donors (avg. 6.3% vs 2.0%, respectively).     

Template‐Assisted Synthesis of π‐Conjugated Molecular Organic Nanowires in the Sub‐100 nm Regime and Device Implications

π‐conjugated molecular organics such as rubrene, Alq₃, fullerene, and PCBM have been used extensively over the last few decades in numerous organic electronic devices, including solar cells, thin‐film transistors, and large‐area, low‐cost flexible displays. Rubrene and Alq₃, have emerged as promising platforms for spin‐based classical and quantum information processing, which has triggered significant research activity in the relatively new area of organic spintronics. Synthesis of these materials in a nanowire geometry, with feature sizes in the sub‐100 nm regime, is desirable as it often enhances device performance and is essential for development of high‐density molecular electronic devices. However, fabrication techniques that meet this stringent size constraint are still largely underdeveloped. Here, a novel, versatile, and reagentless method that enables growth of nanowire arrays of the above‐mentioned organics in the cylindrical nanopores of anodic aluminum oxide (AAO) templates is demonstrated. This method 1) allows synthesis of high‐density organic nanowire arrays on arbitrary substrates, 2) provides electrical access to the nanowire arrays, 3) offers tunability of the array geometry in a range overlapping with the relevant physical length scales of many organic devices, and 4) can potentially be extended to synthesize axially and radially heterostructured organic nanowires. Thus prepared nanowires are characterized extensively with an aim to identify their potential applications in diverse areas such as organic optoelectronics, photovoltaics, molecular nanoelectronics, and spintronics.