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The power conversion efficiency of an ultrathin CuIn_1−ξGa_ξSe_2 (CIGS) solar cell was maximized using a coupled optoelectronic model to determine the optimal bandgap grading of the nonhomogeneous CIGS layer in the thickness direction. The bandgap of the CIGS layer was either sinusoidally or linearly graded, and the solar cell was modeled to have a metallic backreflector corrugated periodically along a fixed direction in the plane. The model predicts that specially tailored bandgap grading can significantly improve the efficiency, with much smaller improvements due to the periodic corrugations. An efficiency of 27.7% with the conventional 2200-nm-thick CIGS layer is predicted with sinusoidal bandgap grading, in comparison to 22% efficiency obtained experimentally with homogeneous bandgap. Furthermore, the inclusion of sinusoidal grading increases the predicted efficiency to 22.89% with just a 600-nm-thick CIGS layer. These high efficiencies arise due to a large electron–hole pair generation rate in the narrow-bandgap regions and the elevation of the open-circuit voltage due to a wider bandgap in the region toward the front surface of the CIGS layer. Thus, bandgap nonhomogeneity, in conjunction with periodic corrugation of the backreflector, can be effective in realizing ultrathin CIGS solar cells that can help overcome the scarcity of indium.

Time-harmonic and time-dependent Green’s functions are derived for a lossless, uniaxial gyroelectromagnetic medium whose permeability tensor is a scalar multiple of its permittivity tensor, and their properties are investigated. The derived Green’s functions can be used for the solution of initial and boundary value problems, as well as for obtaining the electromagnetic fields radiated by electric and magnetic sources.

Absorption of electromagnetic energy by a lossy dielectric slab sitting on a perfectly conducting substrate is examined. It is shown that texturing the exposed surface of the slab by a periodic roughness results in alteration of the absorption characteristics. This alteration is very pronounced, particularly when the mean slab thickness is less than the penetration depth in the slab.

A theory based on Fourier-Bessel expansions and the T-matrix method is presented to compute the reflection and transmission characteristics of dielectric or perfectly conducting cylindrical gratings embedded in a dielectric slab. It is shown that such gratings discriminate quite effectively between TE and TM polarizations even at normal incidence. These results are important in designing semitransparent mirrors for lasers as well as in reflector antenna design.

A procedure based on the T-matrix method is devised to study the electromagnetic response of chiral, (lossy) dielectric, nonspherical objects exposed to an arbitrary incident field. Reductions in the method for axisymmetric objects are discussed. Using the technique thus developed, the plane wave scattering and absorption characteristics of lossy dielectric, axisymmetric scatterers (spheres as well as prolate and oblate spheroids), with and without chiral properties, are examined at frequencies above 50 GHz. The relative permittivity of the objects is assumed to be frequency dependent, whereas the chiral parameters are set to be constant in the numerical study. From the computed results, it appears that chiral spheres are the most effective objects in retarding the progress of an incident plane wave regardless of its polarization.

The newly developed iterative extended boundary condition method (IEBCM) is extended to calculate the scattering by low-loss or lossless elongated dielectric objects. Specifically the iterative procedure is modified so as to utilize an initial assumption of the surface fields obtained from the Mie solution of a spherical object of the same dielectric properties. The solution for the elongated object is obtained by iteratively utilizing the regular EBCM technique to solve for objects of intermediate geometries between the substitute sphere and the object of interest. The other feature of the IEBCM which is related to subdividing the internal volume of the object into several overlapping subregions in each of which a separate field expansion is used is also utilized in the present extension. Results illustrating the adequacy of the IEBCM procedure to calculate the scattering by spheroids of an aspect ratio of more than 7:1 are presented.