We present the growth, fabrication, and photovoltaic characteristics of Inx Ga1−xN/GaN(x∼0.35) multiple quantum well solar cells for concentrator applications. The open circuit voltage, short circuit current density, and solar-energy-to-electricity conversion efficiency were found to increase under concentrated sunlight. The overall efficiency increases from 2.95% to 3.03% when solar concentration increases from 1 to 30 suns and could be enhanced by further improving the material quality.
Photoelectrochemical effects in p-InxGa1−xN (0≤x≤0.22) alloys have been investigated. Hydrogen generation was observed in p-InGaN semiconducting electrodes under white light illumination with additional bias. It was found that p-InGaN alloys possess much higher conversion efficiencies than p-GaN. Time dependent photocurrent density characteristics showed that the stability of p-InGaN in aqueous HBr is excellent. The photocurrent density was found to increase almost linearly with hole mobility and excitation light intensity.
Molybdenum thin films were deposited by rf and dc magnetron sputtering and their properties analyzed with regards to their potential application as a back contact for CIGS solar cells. It is shown that both types of films tend to transition from tensile to compressive strain when the deposition pressure increases, while the conductivity and the grain size decreas. The nucleation of the films characterized byin situand real time spectroscopic ellipsometry shows that both films follow a Volmer-Weber growth, with a higher surface roughness and lower deposition rate for the rf deposited films. The electronic relaxation time was then extracted as a function of bulk layer thickness for rf and dc films by fitting each dielectric function to a Drude free-electron model combined with a broad Lorentz oscillator. The values were fitted to a conical growth mode and demonstrated that the rf-deposited films have already smaller grains than the dc films when the bulk layer thickness is 30 nm.
Nanometer-scale deep-level transient spectroscopy (nano-DLTS) is used to simultaneously map the spatial distribution of the E V + 0.47 eV trap in p-type Cu(In,Ga)Se 2 with surface topography, providing a spatially resolved correlation between electrical traps with physical structure. It is demonstrated that the observed E V + 0.47 eV trap properties using nano-DLTS match those seen with conventional macroscopic device-scale DLTS measurements. Additionally, maps of the E V + 0.47 eV trap reveal that this trap is not uniformly distributed and is likely associated with specific grain boundary structures. The combined approach reveals overall trap impact from the local nanometer scale to the device (micrometer-centimeter) scale and correlation with physical structures on the nanometer-scale that can be broadly applied to any semiconductor material.Index Terms-Cu(In, Ga)Se 2 (CIGS), deep levels, nano-DLTS, thin-film solar cell.
Real time spectroscopic ellipsometry (RTSE) has been applied for in-situ monitoring and analysis of all three processing stages in the co-evaporation of copper indium-gallium diselenide (CuIn 1-x Ga x Se 2 ; CIGS) for high efficiency photovoltaic devices. The first stage entails indium-gallium selenide (In 1-x Ga x ) 2 Se 3 (IGS) deposition at a substrate temperature of 400˚C on soda lime glass coated with opaque Mo. In this stage, an accurate deposition rate and the final IGS bulk and surface roughness layer thicknesses can be obtained. In the second stage, co-evaporation of Cu and Se converts the IGS film to CIGS at an elevated substrate temperature of 570°°°°C. A bulk layer conversion model is justified and employed to analyze the second-stage RTSE data, resulting in steady-state IGS-to-CIGS thickness and volume fraction conversion rates. Near the end of the second stage, the formation of a Cu 2-x Se layer on the CIGS surface can be tracked in terms of an effective thickness rate. The final Cu 2-x Se effective thickness at the CIGS surface is obtained in a time interval spanning the end of the second stage to the beginning of the third. Finally, in the third stage, the Curich CIGS/Cu 2-x Se is converted to slightly Cu-poor CIGS by coevaporation of In, Ga, and Se. In this stage, the thickness conversion rate, and the endpoint bulk and surface roughness layer thicknesses can be obtained. In the three stages, the thickness rates and final thicknesses yield information on the total elemental fluxes, and the roughness evolution yields information on grain growth and near-surface coalescence processes. Modeling of the dielectric functions in future studies is expected to yield compositional information and thus relative metallic fluxes. Variations in the RTSE-deduced information can yield insights into run-to-run irreproducibilities that influence the solar cell performance. The application of these capabilities in the fabrication of solar cells with thick (2.5 µ µ µ µm) and thin (0.3 µ µ µ µm) absorbers is demonstrated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.