Multijunction solar cell with intermediate IR reflector

In the present work, for a system with the sunlight spectrum splitting, a multilayer mirror built-in into the GaInP/Ga(In)As/Ge TJ SC structure is proposed as a selective optical mirror. The function of such a mirror is to extract the IR part of the radiation in the wavelength range of 900-1100 nm from the SC structure for its following utilization by a SC based on Si or InGaAs. Being located between the middle GaAs and the bottom Ge subcells, the mirror based on doubled Bragg reflector (2BR) decreases controllably the portion of IR radiation incident on the Ge subcell and creating conditions for matching the Ge subcell photocurrent with the photocurrents of two other subcells in a TJ SC. The merit of the proposed approach is the entire absence of additional radiation losses in the ranges of the top GaInP and middle GaAs subcells sensitivity (usually resulting from diffraction effects in dichoric mirrors), which conserves their photocurrent at the maximum achievable level without violation of the current matching conditions. Thus, the efficiency of a TJ SC with 2BRs remains practically unchangeable compared with that of a conventional cell structure. The efficiency of 36.6% is demonstrated for a pair of cells: GaInP/Ga)(In)As/2BR/Ge TJ (32.6%) and Si SJ (4%) the latter being operated under the radiation reflected by a 2BR.