Z H Chen, Wencong Yan, Xinyi Li, JL Long, Qiangjian Sun, Min Zhou, Xiaoxu Wu, Menglu Yu, Qing Gong, Erpeng Li, Wenhao Miao, Changwu Ge, Shulong Lu
To achieve high efficiency in five-junction solar cells under a space spectrum, it is essential to precisely adjust the subcells' bandgap to achieve optimal spectral matching. In this work, strain-balanced quantum wells (QWs) are employed to fine-tune the bandgap combination of inverted metamorphic (IMM) four-junction solar cells, which are based on the top four junctions of IMM five-junction solar cells. The 60-period QWs expand the absorption spectrum of the current-limited GaAs subcell to longer wavelengths, resulting in an external quantum efficiency of 48%. The short-circuit current density of the GaAs subcell increased from 10.283 to 11.171 mA/cm2. Consequently, the maximum current mismatch of the four-junction solar cells decreased from 12.2% to 4.6%. We have successfully prepared a flexible four-junction solar cell with a photoelectric conversion efficiency of 30.14% (8 cm2, AM0 spectrum), an open-circuit voltage of 4.347 V, and a retention rate of bending test performance that is over 99%. Based on the performance parameters of the four-junction QW cells, we estimate that the efficiency of the flexible five-junction solar cells prepared on this basis will be further improved.