Metal-oxide (MO) semiconductors have emerged as enabling materials for next generation thin-film electronics owing to their high carrier mobilities, even in the amorphous state, large-area ...uniformity, low cost, and optical transparency, which are applicable to flat-panel displays, flexible circuitry, and photovoltaic cells. Impressive progress in solution-processed MO electronics has been achieved using methodologies such as sol gel, deep-UV irradiation, preformed nanostructures, and combustion synthesis. Nevertheless, because of incomplete lattice condensation and film densification, high-quality solution-processed MO films having technologically relevant thicknesses achievable in a single step have yet to be shown. Here, we report a low-temperature, thickness-controlled coating process to create high-performance, solution-processed MO electronics: spray-combustion synthesis (SCS). We also report for the first time, to our knowledge, indium-gallium-zinc-oxide (IGZO) transistors having densification, nanoporosity, electron mobility, trap densities, bias stability, and film transport approaching those of sputtered films and compatible with conventional fabrication (FAB) operations.
Significance Although impressive progress in solution-processed metal-oxide (MO) electronics has been achieved, fundamental science challenges remain concerning whether solution-processed MO materials and particularly technologically relevant, indium-gallium-tin-oxide (IGZO), can achieve efficient and stable charge transport characteristics when processed at low temperatures for short times and how IGZO film density, porosity, carrier mobility, and charge trapping can be manipulated. Here, we report a coating technique, spray-combustion synthesis, and demonstrate IGZO semiconductor thickness, densification, nanoporosity, electron mobility, trap densities, and bias stress stability approaching the quality of sputtered films.
Ultra‐flexible and transparent metal oxide transistors are developed by doping In2O3 films with poly(vinylphenole) (PVP). By adjusting the In2O3:PVP weight ratio, crystallization is frustrated, and ...conducting pathways for efficient charge transport are maintained. In2O3:5%PVP‐based transistors exhibit mobilities approaching 11 cm2 V−1 s−1 before, and retain up to ca. 90% performance after 100 bending/relaxing cycles at a radius of 10 mm.
Nonlinear optical responses of materials play a vital role for the development of active nanophotonic and plasmonic devices. Optical nonlinearity induced by intense optical excitation of mobile ...electrons in metallic nanostructures can provide large-amplitude, dynamic tuning of their electromagnetic response, which is potentially useful for all-optical processing of information and dynamic beam control. Here we report on the sub-picosecond optical nonlinearity of indium tin oxide nanorod arrays (ITO-NRAs) following intraband, on-plasmon-resonance optical pumping, which enables modulation of the full-visible spectrum with large absolute change of transmission, favourable spectral tunability and beam-steering capability. Furthermore, we observe a transient response in the microsecond regime associated with slow lattice cooling, which arises from the large aspect-ratio and low thermal conductivity of ITO-NRAs. Our results demonstrate that all-optical control of light can be achieved by using heavily doped wide-bandgap semiconductors in their transparent regime with speed faster than that of noble metals.
Light–matter interaction at the nanoscale is of particular interest for future photonic integrated circuits and devices with applications ranging from communication to sensing and imaging. In this ...Letter a combination of transient absorption (TA) and the use of third harmonic generation as a probe (THG-probe) has been adopted to investigate the response of the localized surface plasmon resonances (LSPRs) of vertically aligned indium tin oxide rods (ITORs) upon ultraviolet light (UV) excitation. TA experiments, which are sensitive to the extinction of the LSPR, show a fluence-dependent increase in the frequency and intensity of the LSPR. The THG-probe experiments show a fluence-dependent decrease of the LSPR-enhanced local electric field intensity within the rod, consistent with a shift of the LSPR to higher frequency. The kinetics from both TA and THG-probe experiments are found to be independent of the fluence of the pump. These results indicate that UV excitation modulates the plasma frequency of ITO on the ultrafast time scale by the injection of electrons into, and their subsequent decay from, the conduction band of the rods. Increases to the electron concentration in the conduction band of ∼13% were achieved in these experiments. Computer simulation and modeling have been used throughout the investigation to guide the design of the experiments and to map the electric field distribution around the rods for interpreting far-field measurement results.
The design of a dye-sensitized solar cell (DSSC) based on the simultaneous incorporation of multiple dyes is examined. By investigating the use of the porphyrin-based YD2-o-C8 and YDD6, and the ...organic chromophore TTAR, which can act as complementary absorbers, we are able to enhance the capture of incoming light across the solar spectrum. This is demonstrated first by using a conventional DSSC architecture with a liquid electrolyte and performed a power conversion efficiency (PCE) of 11.2%, representing an improvement over cells based on each of the independent dyes. Next, we used Cs2SnI6 as an encapsulating layer over the sensitizing molecules to reduce charge leakage across the dye layers and also added to the absorption of longer wavelengths up to one micron. Finally, we fabricated a cell utilizing a Cs2SnI6/succinonitrile solid hole-transport electrolyte and achieved a PCE of ∼8.5%. It is expected that the all solid-state design will go a long way toward improving long-term device stability.
Polymer doping of solution‐processed In2O3 with small amounts of the electron‐rich polymer, polyethylenimine (PEI), affords superior transistor performance, including higher electron mobility than ...that of the pristine In2O3 matrix. PEI doping of In2O3 films not only frustrates crystallization and controls the carrier concentration but, more importantly, acts as electron dopant and/or scattering center depending on the polymer doping concentration. The electron donating capacity of PEI combined with charge trapping and variation in the matrix film microstructure yields, for optimum PEI doping concentrations of 1.0%–1.5%, electron mobilities as high as ≈9 cm2 V−1 s−1 on a 300 nm SiO2 gate dielectric, an excellent on/off ratio of ≈107, and an application optimal V
T. Importantly, these metrics exceed those of the pure In2O3 matrix with a maximum mobility ≈4 cm2 V−1 s−1. Furthermore, we show that this approach is extendible to other oxide compositions such as IZO and the technologically relevant IGZO. This work opens a new means to fabricate amorphous semiconductors via solution processing at low temperatures, while preserving or enhancing the mobility of the pristine polycrystalline semiconductor.
Enhanced metal oxide (In2O3, IZO, IGZO) transistor performance via polyethylenimine (PEI) doping is demonstrated for the first time. Unlike previous doping methods for metal oxides, PEI doping not only effectively frustrates crystallization and controls the carrier concentration but also increases the electron mobility of the metal oxide matrix. The PEI electron donating capacity combined with charge trapping and variation in the matrix film microstructure result, for proper PEI doping levels, in high electron mobility and optimal TFT off‐currents and threshold voltages.
Rational creation of polymeric semiconductors from novel building blocks is critical to polymer solar cell (PSC) development. We report a new series of bithiopheneimide-based donor–acceptor ...copolymers for bulk-heterojunction (BHJ) PSCs. The bithiopheneimide electron-deficiency compresses polymer bandgaps and lowers the HOMOsessential to maximize power conversion efficiency (PCE). While the dithiophene bridge progression R2Si→R2Ge minimally impacts bandgaps, it substantially alters the HOMO energies. Furthermore, imide N-substituent variation has negligible impact on polymer opto-electrical properties, but greatly affects solubility and microstructure. Grazing incidence wide-angle X-ray scattering (GIWAXS) indicates that branched N-alkyl substituents increased polymer π–π spacings vs linear N-alkyl substituents, and the dithienosilole-based PBTISi series exhibits more ordered packing than the dithienogermole-based PBTIGe analogues. Further insights into structure–property–device performance correlations are provided by a thieno3,4-cpyrrole-4,6-dione (TPD)–dithienosilole copolymer PTPDSi. DFT computation and optical spectroscopy show that the TPD-based polymers achieve greater subunit–subunit coplanarity via intramolecular (thienyl)S···O(carbonyl) interactions, and GIWAXS indicates that PBTISi-C8 has lower lamellar ordering, but closer π–π spacing than does the TPD-based analogue. Inverted BHJ solar cells using bithiopheneimide-based polymer as donor and PC71BM as acceptor exhibit promising device performance with PCEs up to 6.41% and V oc > 0.80 V. In analogous cells, the TPD analogue exhibits 0.08 V higher V oc with an enhanced PCE of 6.83%, mainly attributable to the lower-lying HOMO induced by the higher imide group density. These results demonstrate the potential of BTI-based polymers for high-performance solar cells, and provide generalizable insights into structure–property relationships in TPD, BTI, and related polymer semiconductors.
Epsilon-near-zero materials may be synthesized as colloidal nanocrystals which display large magnitude subpicosecond switching of infrared localized surface plasmon resonances. Such nanocrystals ...offer a solution-processable, scalable source of tunable metamaterials compatible with arbitrary substrates. Under intraband excitation, these nanocrystals display a red-shift of the plasmon feature arising from the low electron heat capacities and conduction band nonparabolicity of the oxide. Under interband pumping, they show in an ultrafast blueshift of the plasmon resonance due to transient increases in the carrier density. Combined with their high-quality factor, large changes in relative transmittance (+86%) and index of refraction (+85%) at modest control fluences (<5 mJ/cm2) suggest that these materials offer great promise for all-optical switching, wavefront engineering, and beam steering operating at terahertz switching frequencies.
Bulk‐heterojunction organic photovoltaic materials containing nonfullerene acceptors (NFAs) have seen remarkable advances in the past year, finally surpassing fullerenes in performance. Indeed, ...acceptors based on indacenodithiophene (IDT) have become synonymous with high power conversion efficiencies (PCEs). Nevertheless, NFAs have yet to achieve fill factors (FFs) comparable to those of the highest‐performing fullerene‐based materials. To address this seeming anomaly, this study examines a high efficiency IDT‐based acceptor, ITIC, paired with three donor polymers known to achieve high FFs with fullerenes, PTPD3T, PBTI3T, and PBTSA3T. Excellent PCEs up to 8.43% are achieved from PTPD3T:ITIC blends, reflecting good charge transport, optimal morphology, and efficient ITIC to PTPD3T hole‐transfer, as observed by femtosecond transient absorption spectroscopy. Hole‐transfer is observed from ITIC to PBTI3T and PBTSA3T, but less efficiently, reflecting measurably inferior morphology and nonoptimal energy level alignment, resulting in PCEs of 5.34% and 4.65%, respectively. This work demonstrates the importance of proper morphology and kinetics of ITIC → donor polymer hole‐transfer in boosting the performance of polymer:ITIC photovoltaic bulk heterojunction blends.
Three high‐fill‐factor OPV polymers, PTPD3T, PBTI3T, and PBTSA3T are paired with the high performance acceptor, ITIC. A maximum power conversion efficiency of 8.43% is achieved with PTPD3T:ITIC blends due primarily to increased short‐circuit current density. Ultrafast hole‐transfer from ITIC to PTPD3T is observed by femtosecond transient absorption measurements due to the superior blend morphology and improved charge transport versus PBTI3T:ITIC and PBTSA3T:ITIC blends.
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