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Bai, Yang

Publications and source records attributed to Bai, Yang.

At least 73 records · Page 4
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DOE OSTI2016

Phenomenology of strongly coupled chiral gauge theories

A sector with QCD-like strong dynamics is common in models of non-standard physics. Such a model could be accessible in LHC searches if both confinement and big-quarks charged under the confining group are at the TeV scale. Big-quark masses at this scale can be explained if the new fermions are chiral under a new U(1)' gauge symmetry such that their bare masses are related to the U(1)'-breaking and new confinement scales. Here we present a study of a minimal GUT-motivated and gauge anomaly-free model with implications for the LHC Run 2 searches. We find that the first signatures of such models could appear as two gauge boson resonances. The chiral nature of the model could be confirmed by observation of a Z'γ resonance, where the Z' naturally has a large leptonic branching ratio because of its kinetic mixing with the hypercharge gauge boson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Enhancing stability and efficiency of perovskite solar cells with crosslinkable silane-functionalized and doped fullerene

The instability of hybrid perovskite materials due to water and moisture arises as one major challenge to be addressed before any practical application of the demonstrated high efficiency perovskite solar cells. Here we report a facile strategy that can simultaneously enhance the stability and efficiency of p-i-n planar heterojunction-structure perovskite devices. Crosslinkable silane molecules with hydrophobic functional groups are bonded onto fullerene to make the fullerene layer highly water-resistant. Methylammonium iodide is introduced in the fullerene layer for n-doping via anion-induced electron transfer, resulting in dramatically increased conductivity over 100-fold. With crosslinkable silane-functionalized and doped fullerene electron transport layer, the perovskite devices deliver an efficiency of 19.5% with a high fill factor of 80.6%. Furthermore, a crosslinked silane-modified fullerene layer also enhances the water and moisture stability of the non-sealed perovskite devices by retaining nearly 90% of their original efficiencies after 30 days’ exposure in an ambient environment.

14 SOLAR ENERGY↗
DOE OSTI2016

Low Temperature Solution‐Processed Sb:SnO 2 Nanocrystals for Efficient Planar Perovskite Solar Cells

Abstract Inorganic metal oxide electron‐transport layers (ETLs) have the potential to yield perovskite solar cells with improved stability, but generally need high temperature to form conductive and defect‐less forms, which is not compatible with the fabrication of flexible and tandem solar cells. Here, we demonstrate a facile strategy for developing efficient inorganic ETLs by doping SnO 2 nanocrystals (NCs) with a small amount of Sb using a low‐temperature solution‐processed method. The electrical conductivity was remarkably enhanced by Sb‐doping, which increased the carrier concentration in Sb:SnO 2 NCs. Moreover, the upward shift of the Fermi level owing to doping results in improved energy level alignment, which led to reduced charge recombination, and thus longer electron recombination lifetime and improved open‐circuit voltage ( V OC ). Therefore, Sb‐doping of SnO 2 significantly enhanced the photovoltaic performance of planar perovskite devices by increasing the fill factor and V OC , and reducing photocurrent hysteresis, extending the potential application of low‐temperature‐processed ETLs in future flexible and tandem solar cells.

Bai, Yang↗
DOE OSTI2016

Efficient semitransparent perovskite solar cells for 23.0%-efficiency perovskite/silicon four-terminal tandem cells

Here, we have investigated semi-transparent perovskite solar cells and infrared enhanced silicon heterojunction cells for high-efficiency tandem devices. A semi-transparent metal electrode with good electrical conductivity and optical transparency has been fabricated by thermal evaporation of 7 nm of Au onto a 1-nm-thick Cu seed layer. For this electrode to reach its full potential, MAPbI3 thin films were formed by a modified one-step spin-coating method, resulting in a smooth layer that allowed the subsequent metal thin film to remain continuous. The fabricated semi-transparent perovskite solar cells demonstrated 16.5% efficiency under one-sun illumination, and were coupled with infrared-enhanced silicon heterojunction cells tuned specifically for perovskite/Si tandem devices. A double-layer antireflection coating at the front side and MgF2 reflector at rear side of the silicon heterojunction cells reduced parasitic absorption of near-infrared light, leading to 6.5% efficiency after filtering with a perovskite device and 23.0% summed efficiency for the perovskite/Si tandem device.

25 ENERGY STORAGE↗
DOE OSTI2016

Superbumps

For a wide range of supersymmetric models, there is a chiral superfield whose scalar and pseudo-scalar have approximately degenerate masses and couplings to Standard Model particles. At colliders, they may show up as “superbumps”: a pair of resonances with similar masses and production cross-sections. Observing the superbumps may provide evidence of supersymmetry even without seeing superpartners with a different spin. We present two models which realize the superbump scenario. The first one contains an elementary superfield, 24, under SU(5) GUT , while the second one is based on the supersymmetric QCD model with N f = N c + 1 and identifying SU(N f = 5) as SU(5) GUT . Both models have rich phenomenology including nearly mass-degenerate scalar and pseudo-scalar color octets that appear as resonances of two gluons or one gluon plus one photon. As a result, we also show that the recent 750 GeV diphoton excess at the LHC could be the first hint of a superbump signature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Enhanced efficiency and stability of inverted perovskite solar cells using highly crystalline SnO 2 nanocrystals as the robust electron-transporting layer

Here highly crystalline SnO 2 is demonstrated to serve as a stable and robust electron-transporting layer for high-performance perovskite solar cells. Benefiting from its high crystallinity, the relatively thick SnO 2 electron-transporting layer (≈120 nm) provides a respectable electron-transporting property to yield a promising power conversion efficiency (PCE)(18.8%) Over 90% of the initial PCE can be retained after 30 d storage in ambient with ≈70% relative humidity.

14 SOLAR ENERGY↗
DOE OSTI2016

Thin-film semiconductor perspective of organometal trihalide perovskite materials for high-efficiency solar cells

Organolead trihalide perovskites (OTPs) are arising as a new generation of low-cost active materials for solar cells with efficiency rocketing from 3.5% to over 20% within only five years. From “dye” in dye sensitized solar cells to “hole conductors” and “electron conductors” in mesoscopic heterojunction solar cells, there has been a dramatic conceptual evolution on the function of OTPs in photovoltaic devices. OTPs were originally used as dyes in Gratzel cells, achieving a high efficiency above 15% which, however, did not manifest the excellent charge transport properties of OTPs. An analogy of OTPs to traditional semiconductors was drawn after the demonstration of highly efficient planar heterojunction structure OTP devices and the observation of their excellent bipolar transport properties with a large diffusion length exceeding 100 nm in CH 3 NH 3 PbI 3 (MAPbI 3 ) polycrystalline thin films. Here, this review aims to provide the most recent advances in the understanding of the origin of the high OTP device efficiency. Specifically we will focus on reviewing the progress in understanding 1) the characterization of fantastic optoelectronic property of OTPs, 2) the unusual defect physics that originate the optoelectronic property; 3) morphology control of the perovskite film from fabrication process and film post-treatment, and 4) device interface and charge transport layers that dramatically impact device efficiency in the OTP thin film devices; 5) photocurrent hysteresis; 6) tandem solar cells; 7) stability of the perovskite materials and solar cell devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Geometric compatibility of IceCube TeV-PeV neutrino excess and its galactic dark matter origin

Here, we perform a geometric analysis for the sky map of the IceCube TeV-PeV neutrino excess and test its compatibility with the sky map of decaying dark matter signals in our galaxy. Furthermore, we have found that a galactic decaying dark matter component in general improve the goodness of the fit of our model, although the pure isotropic hypothesis has a better fit than the pure dark matter one. Finally, we also consider several representative decaying dark matter, which can provide a good t to the observed spectrum at IceCube with a dark matter lifetime of around 12 orders of magnitude longer than the age of the universe.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Spectrum-doubled heavy vector bosons at the LHC

We study a simple effective field theory incorporating six heavy vector bosons together with the standard-model field content. The new particles preserve custodial symmetry as well as an approximate left-right parity symmetry. The enhanced symmetry of the model allows it to satisfy precision electroweak constraints and bounds from Higgs physics in a regime where all the couplings are perturbative and where the amount of fine-tuning is comparable to that in the standard model itself. We find that the model could explain the recently observed excesses in di-boson processes at invariant mass close to 2TeV from LHC Run 1 for a range of allowed parameter space. The masses of all the particles differ by no more than roughly 10%. In a portion of the allowed parameter space only one of the new particles has a production cross section large enough to be detectable with the energy and luminosity of Run 1, both via its decay to WZ and to Wh, while the others have suppressed production rates. Furthermore, the model can be tested at the higher-energy and higher-luminosity run of the LHC even for an overall scale of the new particles higher than 3TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Stabilized wide bandgap MAPbBr x I 3-x perovskite by enhanced grain size and improved crystallinity

In this study, the light instability of CH 3 NH 3 PbI x Br 3–x has been raised one of the biggest challenges for its application in tandem solar cells. Here we show that an improved crystallinity and grain size of CH 3 NH 3 PbI x Br 3–x films could stabilize these materials under one sun illumination, improving both the efficiency and stability of the wide-bandgap perovskite solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Cosmological constraints on the gravitational interactions of matter and dark matter

Although there is overwhelming evidence of dark matter from its gravitational interaction, we still do not know its precise gravitational interaction strength or whether it obeys the equivalence principle. Using the latest available cosmological data and working within the framework of ΛCDM, we first update the measurement of the multiplicative factor of cosmology-relevant Newton’s constant over the standard laboratory-based value and find that it is consistent with one. In general relativity, dark matter equivalence principle breaking can be mimicked by a long-range dark matter force mediated by an ultra light scalar field. Using the Planck three year data, we find that the dark matter “fifth-force” strength is constrained to be weaker than 10{sup −4} of the gravitational force. We also introduce a phenomenological, post-Newtonian two-fluid description to explicitly break the equivalence principle by introducing a difference between dark matter inertial and gravitational masses. Depending on the decoupling time of the dark matter and ordinary matter fluids, the ratio of the dark matter gravitational mass to inertial mass is constrained to be unity at the 10{sup −6} level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗