Development of ZnTe as a back contact material for thin film cadmium telluride solar cells

Cadmium telluride (CdTe) is high-efficiency commercialised thin film photovoltaic technology. However, developing a stable low-resistivity back contact to the CdTe solar cells is still an issue. High work function and low level of doping of this material don't allow to create an ohmic contact with metals directly. Copper is commonly used to lower the back contact barrier in CdTe solar cells, but an excessive amount of copper diffusing through the cell is harmful for the device performance and stability. In this work a copper-doped ZnTe (ZnTe:Cu) buffer layer was incorporated in between CdTe and gold metal contact by high-rate pulsed DC magnetron sputtering. The back contact was then activated by rapid thermal processing (RTP) resulting in spectacular improvement in key device performance indicators, open circuit voltage (VOC) and fill factor (FF)

Structural and chemical characterization of the back contact region in high efficiency CdTe solar cells

Cadmium telluride (CdTe) is the leading commercialized thin-film photovoltaic technology. Copper is commonly used in back contacts to obtain high efficiency, but has also been implicated as a harmful factor for device stability. T hus it is critical to understand its composition and distribution within complete devices. In this work the composition and structure of the back contact region was examined in high efficiency devices (-16%) contacted using a ZnTe:Cu buffer layer followed by gold metallization. T he microstructure was examined in the asdeposited state and after rapid thermal processing (RTP) using high resolution transmission electron microscopy and EDX chemical mapping. After RTP the ZnTe exhibits a bilayer structure with polycrystalline, twinned grains adjacent to Au and an amorphous region adjacent to CdTe characterized by extensive Cd-Zn interdiffusion. T he copper that is co-deposited uniformly within ZnTe is found to segregate dramatically after RTP activation, either collecting near the ZnTe/Au interface or forming CUxTe clusters in CdTe at defects or grain boundaries near the interface with ZnTe. Chlorine, present throughout CdTe and concentrated at grain boundaries, does not penetrate significantly into the back contact region during RTP activation

Thermochromic Metal Halide Perovskite Windows with Ideal Transition Temperatures

Urban centers across the globe are responsible for a significant fraction of energy consumption and CO2 emission. As urban centers continue to grow, the popularity of glass as cladding material in urban buildings is an alarming trend. Dynamic windows reduce heating and cooling loads in buildings by passive heating in cold seasons and mitigating solar heat gain in hot seasons. In this work, we develop a mesoscopic building energy model that demonstrates reduced building energy consumption when thermochromic windows are employed. Savings are realized across eight disparate climate zones of the United States. We use the model to determine the ideal critical transition temperature of 20 to 27.5 {\deg}C for thermochromic windows based on metal halide perovskite materials. Ideal transition temperatures are realized experimentally in composite metal halide perovskite film composed of perovskite crystals and an adjacent reservoir phase. The transition temperature is controlled by co-intercalating methanol, instead of water, with methylammonium iodide and tailoring the hydrogen-bonding chemistry of the reservoir phase. Thermochromic windows based on metal halide perovskites represent a clear opportunity to mitigate the effects of energy-hungry buildings

Alveolar Rhabdomyosarcoma with Regional Nodal Involvement: Results of a Combined Analysis from Two Cooperative Groups

BACKGROUND: Treatment of children and adolescents with alveolar rhabdomyosarcoma (ARMS) and regional nodal involvement (N1) have been approached differently by North American and European cooperative groups. In order to define the better therapeutic strategy, we analyzed two studies conducted between 2005 and 2016 by the European paediatric Soft tissue sarcoma Study Group (EpSSG) and Children’s Oncology Group (COG). METHODS: We retrospectively identified patients with ARMS-N1 enrolled in either EpSSG RMS2005 or in COG ARST0531. Chemotherapy in RMS2005 comprised IVADo (ifosfamide, vincristine, dactinomycin, doxorubicin), IVA and maintenance (vinorelbine, cyclophosphamide); in ARST0531 it consisted on either VAC (vincristine, dactinomycin, cyclophosphamide) or VAC alternating with VI (vincristine, irinotecan). Local treatment was similar in both protocols. RESULTS: The analysis of the clinical characteristics of 239 patients showed some differences between study groups: in RMS2005, advanced IRS Group and large tumors predominated. There were no differences in outcomes between the two groups: 5-year event-free survival (EFS), 49%(95%CI=39–59) and 44%(95%CI=30–58), and overall survival (OS), 51%(95%CI=41–61) and 53.6%(95%CI=40–68), in RMS2005 and ARST0531, respectively. In RMS2005, EFS of patients with FOXO1-positive tumors was significantly inferior to those FOXO1-negative (49.3% vs 73%, p=0.034). In contrast, in ARST0531, EFS of patients with FOXO1-positive tumors was 45% compared with 43.8% for those FOXO1-negative. CONCLUSIONS: The outcome of patients with ARMS N1 was similar in both protocols. However, patients with FOXO1 fusion-negative tumors enrolled in RMS2005 showed a significantly better outcome, suggesting that different strategies of chemotherapy may have an impact in the outcome of this subgroup of patients

Low-Temperature Synthesis of <i>n</i>‑Type WS₂ Thin Films via H₂S Plasma Sulfurization of WO₃

Thin tungsten disulfide (WS₂) films were prepared on SnO₂:F (FTO)-coated glass substrates by H₂S plasma sulfurization of sputtered WO₃. The reactive environment provided by the plasma enabled the complete transformation of a 75 nm oxide film to stoichiometric WS₂ within 1 h at 500 °C. An apparent activation energy of 63.6 ± 1.9 kJ/mol was calculated for the plasma conversion process, which is less than half the barrier reported for the reaction of WO₃ with H₂S. The conversion followed Deal–Grove behavior, with the growing WS₂ overlayer hindering diffusion to and from the reactive interface. The calibrated light absorption and relative intensity of the second-order Raman 2LA­(M) peak were identified as two additional methods for progressively monitoring the thickness of the WS₂ layer. The semiconducting WS₂ layers exhibited <i>n</i>-type behavior with an indirect band gap at 1.4 eV and an absorption coefficient of ∼5 × 10⁴ cm^–1. Preliminary electrochemical measurements showed that the presence of WS₂ reduced the overpotential required for the hydrogen evolution reaction by 360 mV relative to FTO while displaying good stability

Synthesis of Stoichiometric FeS₂ through Plasma-Assisted Sulfurization of Fe₂O₃ Nanorods

Pyrite (FeS₂) thin films were synthesized using a H₂S plasma to sulfurize hematite (Fe₂O₃) nanorods deposited by chemical bath deposition. The high S activity within the plasma enabled a direct solid-state transformation between the two materials, bypassing S-deficient contaminant phases (Fe_1–<i>x</i>S). The application of plasma dramatically enhanced both the rate of conversion and the quality of the resulting material; stoichiometric FeS₂ was obtained at a moderate temperature of 400 °C using a chalcogen partial pressure <6 × 10^–5 atm. As the S:Fe atomic ratio increased from 0 to 2.0, the apparent optical band gap dropped from 2.2 (hematite) to ∼1 eV (pyrite), with completely converted layers exhibiting absorption coefficients >10⁵ cm^–1 in the visible range. Room-temperature conductivity of FeS₂ films was on the order of 10^–4 S cm^–1 and approximately doubled under calibrated solar illumination