Detail Analysis of External Quantum Efficiency Measurement for Tandem Junction Solar Cells

The tandem junction solar cells require accurate external quantum efficiency (EQE) measurement to determine the current match condition for high efficiency approach. The EQE measurement of tandem-junction solar cells requires variation of the bias spectrum and voltage biasing. The optimization of bias spectra and adjusted bias voltage are necessary to minimize a measurement artifact due to the simultaneously measured response of another subcell. Additionally, the shape of the spectral response curve is influenced under certain measurement conditions such as bias light and voltage bias. In this paper, the difference between AC and DC mode EQE measurements are compared and the influence of bias light and voltage biasing in EQE measurement are discussed. The bias light and voltage biasing should be applied for short-circuit condition of the subcell under test. The measurement artifact has been thoroughly discussed by measurement results. Therefore, it is possible to understand the origin of the measurement artifact and to give guidelines for its minimization. The EQE spectra with optimization of bias voltage and bias light to minimize the artifact are confirmed with the IV measurement under illumination. To further improve the accretion of EQE measurement, the heating due to the bias light illumination can be taken into consideration.