Characterization of dual-junction III-V on Si tandem solar cells with 23.7% efficiency under low concentration

Monolithic two-terminal III-V on Si dual-junction solar cells, designed for low concentration applications, were fabricated by means of surface-activated direct wafer bonding. The III-V top cell is a heterojunction formed by an n-Ga0.5In0.5P emitter and a p-Al0.2Ga0.8As base. An efficiency of 21.1 +/- 1.5% at one sun and 23.7 +/- 1.7% at 10 suns is demonstrated, which to our knowledge is the best dual-junction two-terminal III-V on Si tandem cell efficiency reported to date under verified reference conditions. The I-V characterization of these 1-cm(2) tandem cells under concentration required the development of a new method using a single-source multiflash solar simulator and not perfectly matched component cells, also known as pseudo-isotypes, formed by Si single-junction cells and optical filters. In addition, the spectrum of the pulsed solar simulator was measured using a high-speed CMOS spectrometer, allowing the calculation of the spectral mismatch correction factor. Merging these two techniques results in the hybrid corrected pseudo-isotype (HCPI) characterization method, which shows a fast and accurate performance with a simplified procedure based on a single-source solar simulator. Pseudo-isotypes are easily adaptable to new cell designs by simply using a different filter, hence allowing the characterization of new multijunction solar cell architectures.