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.

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