Investigation of Group V doping and passivating oxides to reduce the voltage deficit in CdTe solar cells

Includes bibliographical references.2022 Fall.Thin film cadmium telluride is one of the most successful photovoltaic technologies on the market today. Second only to silicon in yearly output and accounting for 40% of U.S. utility-scale photovoltaic installation, CdTe is known for its ease of manufacture, ideal bandgap, and low levelized cost of energy. Despite its commercial success, CdTe underperforms compared to its theoretical potential. The current world record CdTe device is only 21.0% compared to a theoretical maximum of 33.1%. This significant discrepancy in efficiencies can mostly be attributed to the poor open-circuit voltage of CdTe devices. Compared to silicon technologies, CdTe has a large voltage deficiency, exceeding 250 mV. While copper doping has traditionally been used for CdTe devices, it has proven to be incapable of sufficiently doping CdTe. Copper typically dopes CdTe in the 1014 to 1015 holes/cm3 range where most models predict that 1016–1017 is needed. Additionally, interstitial copper is a fast diffuser in CdTe, and can lead to numerous stability issues. As an alternative to copper, this work explores arsenic as a dopant for CdTe. Using a novel arsenic doping technique, hole concentrations greater than 1015 cm-3, microsecond lifetimes, and increased radiative efficiency are achieved. These are important prerequisites to achieving higher voltages. Achieving high doping levels alone is not sufficient to achieve higher device performance. A well-passivated and carrier selective contact is needed to ensure that electron-hole pairs do not recombine and are extracted as useable energy. Aluminum oxide has been shown to passivate CdTe surfaces. This work illustrates the explorations of using Al2O¬3 as a passivation layer, pairing it with highly doped amorphous silicon as a hole contact, resulting in excess-carrier lifetimes up to 8 µs, the highest reported to date for polycrystalline Cd(Se)Te. Although the inclusion of arsenic doping and an aluminum oxide back contact are each explored separately, the combination of both methods result in massive improvements to the carrier lifetime, interface passivation and radiative efficiency. Through this combination, microsecond lifetime and External Radiative Efficiency of over 4% are achieved. The excellent ERE values measured here are indicative of large quasi-Fermi level splitting, leading to an implied voltage with multiple device structures of nearly 1 V and an implied voltage of 25%. Finally, while CdSeTe serves as a more promising photovoltaic absorber candidate compared to CdTe, certain difficulties remain which must be addressed. Careful selection of processing conditions is shown to create a dense and large-grained film while eliminating wurtzite-phase crystal growth, which has been shown to degrade device performance. Surprisingly, as-deposited CdSeTe is shown to be n-type or nearly intrinsic rather than the previously supposed p-type. This necessitates additional steps to account for very poor hole conductivity, which can produce zero-current devices if not addressed. Challenges notwithstanding, CdSeTe absorbers are shown to be a key component in devices capable of a photovoltaic conversion efficiency of greater than 25%

Striation and convection in penumbral filaments

Observations with the 1-m Swedish Solar Telescope of the flows seen in penumbral filaments are presented. Time sequences of bright filaments show overturning motions strikingly similar to those seen along the walls of small isolated structures in the active regions. The filaments show outward propagating striations with inclination angles suggesting that they are aligned with the local magnetic field. We interpret it as the equivalent of the striations seen in the walls of small isolated magnetic structures. Their origin is then a corrugation of the boundary between an overturning convective flow inside the filament and the magnetic field wrapping around it. The outward propagation is a combination of a pattern motion due to the downflow observed along the sides of bright filaments, and the Evershed flow. The observed short wavelength of the striation argues against the existence of a dynamically significant horizontal field inside the bright filaments. Its intensity contrast is explained by the same physical effect that causes the dark cores of filaments, light bridges and `canals'. In this way striation represents an important clue to the physics of penumbral structure and its relation with other magnetic structures on the solar surface. We put this in perspective with results from the recent 3-D radiative hydrodynamic simulations.Comment: Accepted for publication in A&

Advanced co-sublimation hardware for deposition of graded ternary alloys in thin-film applications

© 2018 IEEE. CdTe photovoltaic devices with efficiency over 22% have been demonstrated. Sublimated CdTe photovoltaics with efficiency over 19% have been reported using graded alloying of Se in CdTe absorber films. Grading of alloy films has been identified as an important characteristic to achieve higher device performance using more complex device structures. An advanced co-sublimation source has been designed and developed to deposit highly controlled CdTe based ternary alloys. An advanced shutter mechanism enables changing the composition of the deposited films during sublimation. The hardware used for advanced co-sublimation and initial materials characterization is presented in this study

Phospholamban antisense oligonucleotides improve cardiac function in murine cardiomyopathy

Heart failure (HF) is a major cause of morbidity and mortality worldwide, highlighting an urgent need for novel treatment options, despite recent improvements. Aberrant Ca(2+) handling is a key feature of HF pathophysiology. Restoring the Ca(2+) regulating machinery is an attractive therapeutic strategy supported by genetic and pharmacological proof of concept studies. Here, we study antisense oligonucleotides (ASOs) as a therapeutic modality, interfering with the PLN/SERCA2a interaction by targeting Pln mRNA for downregulation in the heart of murine HF models. Mice harboring the PLN R14del pathogenic variant recapitulate the human dilated cardiomyopathy (DCM) phenotype; subcutaneous administration of PLN-ASO prevents PLN protein aggregation, cardiac dysfunction, and leads to a 3-fold increase in survival rate. In another genetic DCM mouse model, unrelated to PLN (Cspr3/Mlp(−/−)), PLN-ASO also reverses the HF phenotype. Finally, in rats with myocardial infarction, PLN-ASO treatment prevents progression of left ventricular dilatation and improves left ventricular contractility. Thus, our data establish that antisense inhibition of PLN is an effective strategy in preclinical models of genetic cardiomyopathy as well as ischemia driven HF

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV

A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 inverse picobarns collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Z/gamma* + b-jet cross section in pp collisions at 7 TeV

The production of b jets in association with a Z/gamma* boson is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV and recorded by the CMS detector. The inclusive cross section for Z/gamma* + b-jet production is measured in a sample corresponding to an integrated luminosity of 2.2 inverse femtobarns. The Z/gamma* + b-jet cross section with Z/gamma* to ll (where ll = ee or mu mu) for events with the invariant mass 60 < M(ll) < 120 GeV, at least one b jet at the hadron level with pT > 25 GeV and abs(eta) < 2.1, and a separation between the leptons and the jets of Delta R > 0.5 is found to be 5.84 +/- 0.08 (stat.) +/- 0.72 (syst.) +(0.25)/-(0.55) (theory) pb. The kinematic properties of the events are also studied and found to be in agreement with the predictions made by the MadGraph event generator with the parton shower and the hadronisation performed by PYTHIA.Comment: Submitted to the Journal of High Energy Physic

Search for anomalous t t-bar production in the highly-boosted all-hadronic final state

A search is presented for a massive particle, generically referred to as a Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any enhancement in t t-bar production beyond expectations of the standard model for t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version includes a minor typo correction that will be submitted as an erratu

Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV

The t t-bar production cross section (sigma[t t-bar]) is measured in proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS experiment, corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurement is performed in events with two leptons (electrons or muons) in the final state, at least two jets identified as jets originating from b quarks, and the presence of an imbalance in transverse momentum. The measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/- 2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction of the standard model.Comment: Replaced with published version. Included journal reference and DO