Realizing high photovoltaic efficiency with parallel multijunction solar cells based on spectrum-splitting and -concentrating diffractive optical element**Project supported by the National Natural Science Foundation of China (Grant Nos. 91233202, 21173260, and 51072221) and the National Basic Research Program of China (Grant No. 2012CB932903).

Abstract

Based on the facts that multijunction solar cells can increase the efficiency and concentration can reduce the cost dramatically, a special design of parallel multijunction solar cells was presented. The design employed a diffractive optical element (DOE) to split and concentrate the sunlight. A rainbow region and a zero-order diffraction region were generated on the output plane where solar cells with corresponding band gaps were placed. An analytical expression of the light intensity distribution on the output plane of the special DOE was deduced, and the limiting photovoltaic efficiency of such parallel multijunction solar cells was obtained based on Shockley–Queisser’s theory. An efficiency exceeding the Shockley–Queisser limit (33%) can be expected using multijunction solar cells consisting of separately fabricated subcells. The results provide an important alternative approach to realize high photovoltaic efficiency without the need for expensive epitaxial technology widely used in tandem solar cells, thus stimulating the research and application of high efficiency and low cost solar cells.