A new sputtered process for cadmium sulfide (CdS) has been developed that boosted efficiency of a PV device baseline (with single-stage, coevaporated CIGS) by similar to 2.7% (absolute) to an average of similar to 10%. The process is highly scalable to a roll-to-roll environment, with the maximum efficiency effect occurring at 0.1 mbar (similar to 75 mTorr) sputtering pressure. The efficiency improvement is thought to be due to two main factors: composition and defects. The CdS film deposited at high pressure (HP) contains more oxygen (primarily as CdO) than one deposited at typical pressures, with oxygen content higher towards the CdS-CIGS interface. The HP process produces an interface with less CdS-CIGS intermixing, which results in a junction with similar to 5x fewer defects as measured by admittance spectroscopy. The performance improvement due to HP CdS occurs even with a very thin CdS layer (< 15 nm), thus greatly reducing the total amount of cadmium contained in the cells.

This report describes the development of a method for analysis of elemental composition of CIGS on Mo/glass and layer thickness using x-ray fluorescence spectrometry. Calibration standards for XRF were characterized by ICP for CIGS elemental composition and SEM for CIGS and Mo layer thicknesses. Also reported are the results of a precision study evaluating the capability of the XRF and ICP methods using statistical tools, and a comparative study of XRF and ICP results for CIGS composition and XRF and SEM for layer thickness determination. The results of the evaluation indicate that the precision obtained by XRF allows for resolution of smaller differences in CIGS composition than ICP, and in layer thickness than SEM. The recoveries of the XRF CIGS compositional analysis versus ICP range from 95 – 105%. A comparison of the XRF layer thickness results vs. SEM gave recoveries that range from 91 to 103%.

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

S.W. Magennis a, A.J. Ferguson b, T. Bryden b, T.S. Jones b, A. Beeby c,∗, I.D.W. Samuel a,∗ a Ultrafast Photonics Collaboration, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, UK b Ultrafast Photonics Collaboration, Centre for Electronic Materials and Devices, Department of Chemistry, Imperial College, London SW7 2AY, UK c Department of Chemistry, University of Durham, South Road, Durham DHI 3LE, UK

Polymeric, planar waveguides of pyrromethene dye 1,3,5,7, 8-pentamethyl-2, 6-diethylpyrromethene-BF2 (PM567)-doped poly(methylmethacrylate) (PMMA) were prepared by spin coating (SC) and solution diffusion (SD) methods. Both techniques produced films that, under laser illumination, show strong spectral narrowing due to amplified spontaneous emission (ASE). Samples prepared by SD showed higher gain than the SC films. Also, compared to the SC samples, the smooth surface of the SD samples reduced scattering at the surface and therefore guding losses. The high dye concentration present in the SD samples may be responsible for the increased photostability (more than 105 pulses). The SD method appears to offer a simple alternative for the production of planar wave-guides for amplifier devices.

We report the first time-resolved photoluminescence studies of erbium tris(8-hydroxyquinolate), [ErQ3], as a powder, a thin film blend with polycarbonate, an evaporated film and in DMSO-d6 solution. The 4I13/2→4I15/2 transition at 1.5μm displays biexponential kinetics with photoluminescence lifetimes in the region of 0.2μs for the powder, 0.4μs for the thin film blend, 0.9μs for the evaporated film, and 2μs in solution. These observed lifetimes are much shorter than the natural radiative lifetimes of this Er3+ transition, implying photoluminescence quantum yields that range from 0.002 to 0.03%. This has significant consequences for the device efficiencies achievable by near IR-emitting organic light-emitting diodes (OLEDs) containing [ErQ3] as the emissive layer.

The polymer species formed from the spontaneous polymerization of formaldehyde (H2CO) on clean Cu(100) at 85 K were studied using electron energy loss spectroscopy (EELS) and temperature-programmed desorption (TPD). Formaldehyde forms poly(oxymethylene) (POM) with differing chain lengths; the long (alpha) and short (beta) chain species depolymerize to give two features in TPD at approximately 207 and 219 K, respectively. The complex desorption kinetics observed for the alpha -POM species were successfully modeled using equations based on the ratio of the average number of monomers unzipped from the chain per initiation event to the length of the polymer chain. Losses were observed in EEL spectra of the short-chain species at similar to 290, similar to 1020, and similar to 1120 cm(-1) that can be assigned to the nu (Cu-O), nu (C-O), and rho (CH3) modes of oxygen and methoxy endgroups, respectively. Preadsorbed methanol increases the proportion of short-chain POM species by increasing the probability of termination for the fi species. Lower thermal stability for adsorbed POM was observed compared to bulk POM and is believed to be related to the stability of the surface-bound oxygen endgroup.

The photochemistry of formaldehyde (H2CO) adsorbed on CO-saturated Cu(100) at 85 K was studied using electron energy loss spectroscopy (EELS) and temperature-programmed desorption (TPD). Formaldehyde was weakly adsorbed on CO/Cu(100) desorbing at 104 K with a desorption energy of 18.2 (+/-0.8) kJ/mol. Irradiation of the H2CO/CO/Cu(100) surface caused the molecularly adsorbed H2CO to polymerize, forming poly(oxymethylene) (POM). Irradiation also caused the formation of ethylene glycol (CH2OH)(2). Losses observed at 870 and 3365 cm(-1). after UV irradiation, were assigned to v(CC) and v(OH) modes, respectively, of (CH2OH)(2), indicating ethylene glycol was formed promptly upon irradiation. The presence of (CH2OH)(2) was confirmed by studying the adsorption of (CH2OH)(2) on clean and oxygen-covered Cu(100). The formation of ethylene glycol was likely governed by geometric constraints present within the formaldehyde overlayer.

The adsorption and photochemistry of dibromodifluoromethane (Halon 1202) adsorbed on highly ordered pyrolytic graphite (HOPG) was studied using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Dibromodifluoromethane adsorbs molecularly at 85 K and the first layer saturates at a fractional coverage of 0.14 +/- 0.01 monolayer (ML). Molecular desorption occurs at similar to 140 K (monolayer) and similar to 110 K (multilayers) with desorption energies of 43.8 +/- 3.6 and 22.4 +/- 1.9 kJ/mol, respectively. Ultraviolet irradiation of the monolayer by a filtered Hg-arc lamp (225-350 nm) resulted in the formation of CF2Br and Br (major products) and Br-2 and C2F4Br2 (minor products). The estimated integrated dissociation cross-section was 1.9 x 10(-19) cm(2) close to the calculated value for CF2Br2(g) ( 1.5 x 10(-19) cm(2)). The similarity of these two values implies that photodissociation of CF2Br2(ad)/HOPG is dominated by direct photoabsorption of the adsorbate and not electronic processes moderated by the substrate. The influence of the surface is most clearly observed in the distribution of products measured by TPD. We attribute the differences observed between adsorbate and gas phase/matrix isolation experiments to the high density of photogenerated species trapped in the surface layer.

The adsorption of formaldehyde (H2CO) on clean Cu(100) at 85 K has been studied using electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). For coverages up to (1.06 +/- 0.22) x 10(15) H2CO molecules/cm(2), formaldehyde spontaneously polymerized to form a monolayer of disordered poly(oxymethylene) (POM), arranged with the chain directions parallel to the surface plane. Thermal decompasition/desorption of the polymer monolayer occurred by three routes, producing peaks in temperature-programmed desorption (TPD) at approximately 177, 200, and 215 K. The lowest temperature peak was exclusively associated with production of Hz and CO in approximately equal proportions. The two higher temperature peaks were produced by molecular H2CO generated via depolymerization of the polymer. The 200 and 215 K features displayed zero- and first-order desorption kinetics, corresponding to estimated activation energies for depolymerization of 75 +/- 10 and 53.9 +/- 0.5 kJ/mol, respectively. The presence of two polymer desorption peaks is attributed to chain conformational differences present within the monolayer and has not been previously observed in studies of formaldehyde adsorption on metal surfaces. Large exposures of H2CO on this surface formed multilayers of molecular formaldehyde on top of the first polymer layer. The second layer desorbed at 105 K and subsequent layers at similar to 100 K.