Multi-junction solar cell (MJ) has been paid more attention for space and terrestrial concentrator system applications because of more efficiency has achieved. The spectral response (SR) of MJ is an important characteristic for technique optimization or performance evaluation. Measurement of SR of MJ cell is quite more difficult than that of single-junction solar cell (SJ) because a complicated light biasing and voltage biasing system is needed.
The object to be tested is GaInP/Ga(In)As/Ge triple-junction monolithic cells, and Ge bottom subcell with non-ideal properties would suffer from measurement error by improper voltage biasing. Since monolithic MJ cell without any middle taps, the internal characteristic is inaccessible, so the external biasing voltage usually obtained by estimating. It is well known that the characteristic of semi-conductor device has wide variance range, so significant deviation is often observed by a fixed estimating value. The paper proposes a method which could access the internal characteristic of MJ indirectly based on measuring other than estimating or mathematics model, and it has been proven by experiment with two SJ component cells, Ga(In)As cell and Ge cell.