Solar-cell operation under concentrated illumination

A conventional n⁺-p-p⁺solar-cell structure is analyzed for operation under highly concentrated sunlight and various levels of heat sinking. The electrical characteristics are obtained by solving the temperature-dependent ambipolar carrier flow equations in two dimensions under typical boundary conditions. The thermal problem is solved taking into account Joule heating and cooling as well as thermal effects due to minority carrier generation and recombination and the excess energy of absorbed photons. Photogeneration is calculated using a temperature-dependent model of photon absorption. Lateral potential drops occurring in the thin n⁺top layer are shown to result in an effective reduction of active device area under very high illumination. This effect is enhanced when high-temperature operation is considered. Calculated results showing conversion efficiency as a function of light intensity and temperature are presented along with preliminary findings on the possibility of improving the fill factor by incorporating lateral impurity diffusion profiles in the design.