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Radiative and nonradiative recombination dynamics in strained cubic (c-) In0.1Ga0.9N/c-GaN multiple quantum wells were studied using temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy. In contrast to hexagonal InGaN quantum wells, low-excitation photoluminescence peak energy increased moderately with decreasing well thickness L and the PL lifetime did not strongly depend on L. The results clearly indicated that the piezoelectric field was not acting on the transition process. The TRPL signal was well fitted as a stretched exponential decay from 10 to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures such as In clusters. The localized states were considered to have two-dimensional density of states at 300 K (quantum disk size), since the radiative lifetime increased with increasing temperature above 150 K.

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Visible-light-transparent p-type NiO films were deposited by reactive RF sputtering under unintentional heating. An optical transmittance of >80% was obtained in the wavelength range of 500–800 nm when the films were deposited under a very low O2 fraction in the gas phase O2/(Ar+ O2) = 0.5%. This result may reflect a decrease in the concentration of Ni vacancies due to the increase in their formation energy under oxygen-poor deposition conditions. Heterostructure pn junctions consisting of p-type NiO and n-type ZnO layers were also deposited. We eventually observed a slight but noticeable photovoltaic effect.

In this study, the effects of light-soaking (LS), heat-soaking (HS), and combined LS and HS, that is, heat-light soaking (HLS) on potassium fluoride (KF)-treated and KF-free copper indium gallium selenide (CIGS) solar cells with CBD-CdS buffer layer were investigated. LS and HS did not change the basic solar cell parameters of CIGS solar cells when they were performed separately.In contrast, HLS improved cell efficiency with increased open-circuit-voltage for KF-treated CIGS solar cells, whereas it reduced cell performance for KF-free CIGS cells. Capacitance-voltage measurements confirmed a significantly increased carrier concentration in KF-treated CIGS solar cells, as compared to KF-free cells by HLS. X-ray photoelectron spectroscopy measurement revealed that the HLS did not change the atomic concentration of Cd, S, and O in CBD-CdS buffer layer.However, the concentration of Na atoms slightly increased at the CIGS surface region, as confirmed from SIMS measurement. It implies a possible reason for increased carrier concentration in KF-treated CIGS solar cells after HLS. Temperature-dependent current-voltage measurements suggests that HLS modify a K-containing new layer and affects cell performance.

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The energy band diagrams of NiO-based solar cell structures that use various n-type oxide semiconductors such as ZnO, Mg 0.3 Zn 0.7 O, Zn 0.5 Sn 0.5 O, In 2 O 3 :Sn (ITO), SnO 2 , and TiO 2 were evaluated by photoelectron yield spectroscopy. The valence band discontinuities were estimated to be 1.6 eV for ZnO/NiO and Mg 0.3 Zn 0.7 O/NiO, 1.7 eV for Zn 0.5 Sn 0.5 O/NiO and ITO/NiO, and 1.8 eV for SnO 2 /NiO and TiO 2 /NiO heterojunctions. By using the valence band discontinuity values and corresponding energy bandgaps of the layers, energy band diagrams were developed. Judging from the band diagram, an appropriate solar cell consisting of p-type NiO and n-type ZnO layers was deposited on ITO, and a slight but noticeable photovoltaic effect was obtained with an open circuit voltage (V oc ) of 0.96 V, short circuit current density (J sc ) of 2.2 lA/cm 2 , and fill factor of 0.44. V C 2014 AIP Publishing LLC. [http://dx.