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ABSTRACT Thin CdTe photovoltaic device efficiencies show significant improvement with the incorporation of a CdSeTe alloy layer deposited between a MgZnO emitter and CdTe absorber. CdTe and CdSeTe/CdTe devices fabricated by close-space sublimation with a total absorber thickness of 1.5 µm are studied using microscopy measurements and show minimal diffusion of Se into the CdTe. Current loss analysis shows that the CdSeTe layer is the primary absorber in the CdSeTe/CdTe structure, and fill factor loss analysis shows that ideality-factor reduction is the dominant mechanism of fill factor loss. Improvement in the CdSeTe/CdTe absorber quality compared to CdTe is also reflected in spectral and time-resolved photoluminescence measurements. Current density vs. voltage measurements show an increase in current density of up to 2 mA/cm 2 with the addition of CdSeTe due to a band gap shift from 1.5 to 1.42 eV for CdTe and CdSeTe/CdTe absorbers respectively. Voltage deficit is lower with the incorporation of the CdSeTe layer, corroborated by improved electroluminescence intensity. The addition of CdSeTe into CdTe device structures has increased device efficiencies from 14.7% to 15.6% for absorbers with a total thickness less than two microns. 

As more emphasis is placed on thinner gauges and stronger steel grades for more fuel efficient, and crash-worthy vehicles, corrosion becomes a more important consideration. This demand has led to the development of advanced high strength steel (AHSS) grades such as dual-phase (DP) and transformation-induced plasticity (TRIP) aided steels. To protect these steels from corrosion, a hot-dip galvanizing (HDG) or galvannealing (GA) process is employed. However, alloying with Mn and Si can cause complex surface oxides during annealing, which may result in defects in the zinc coating1-8. In order to increase AHSS galvanizability, selective oxidation of alloying elements in DP and TRIP-aided steel needs to be understood. Depending on annealing atmosphere, the mechanism (internal or external) of oxidation can change, as well as the thermodynamic stability of the oxide. Wagner’s theory of oxidation enables prediction of the mechanism of oxidation for binary oxide systems9. The defects can be present after pickling and fluxing, causing wettability issues during the HDG process. Coating defects may also form or be further exacerbated by the galvannealing operation. For this work, oxidation mechanism predictions were performed using Wagner’s theory of oxidation. In the present study a 0.07C-1.9Mn-0.2Si-0.3Cr galvannealed dual-phase steel which exhibited streaking defects in the coating was analyzed. Light optical metallography (LOM) and scanning electron microscopy (SEM) were performed to characterize defects within the galvannealed coating. Static spectra and 3-D profiling using time of flight secondary ion mass spectrometry (TOF-SIMS) was employed. It was found that Mn rich Si containing oxides are present on the steel-coating interface. It does not appear that these oxides affect wettability, however they may have an influence on intermetallic growth during galvannealing. This, combined with an influence from the micro-grooves of the sink roll in the Zn pot, may lead to the streaking defects observed. 

CdMgTe with a 1.8-eV band gap was deposited at the back of MgZnO/CdSeTe/CdTe superstrates to create a conduction band barrier and reduce back surface recombination. To minimize CdCl2 passivation loss, substrate preheat time was varied. Photoluminescence, carrier lifetime, and quantum efficiency showed improvement with shorter preheat and secondary ion mass spectrometry profiles showed retention of CdCl2 passivation for short CdMgTe preheat. An HCl acid etch treatment and CdTe cap layer were incorporated independently after the CdMgTe on additional devices to minimize magnesium oxidation and the CdTe cap device showed initial promise with device efficiency reaching 13.1%.