The external quantum efficiency of quantum well solar cells （QWSCs） is compared with the control cells without multi-quantum wells. The QWSCs extend the absorption spectrum from 870 to 1000nm. When the wavelength is below 680nm,the external quantum efficiency of the QWSCs is lower than that of the control cells, but when the wavelength is above 680nm, the external quantum efficiency of the QWSCs is higher than that of the control cells. The possible reasons for this phenomenon are discussed. Basing on the experimental data,the possibility of substituting the middle cells of conventional triple-junction solar cells with the QWSCs to improve their performance is also discussed.
