Measurement of subcell depletion layer capacitances in multijunction solar cells

Abstract

A method for measuring subcell capacitance voltage (C–V) in a multijunction solar cell is introduced. The subcell of interest is illuminated by a monochromatic light pulse with a ns rise time. The subcell capacitance is calculated from the measured rise time of the solar cell voltage. The effect of optical coupling is eliminated by introducing a high intensity bias illumination to all subcells below the one measured. The method is verified by comparing the subcell capacitance obtained from four junction solar cells with the results from corresponding component cells, which can be measured using well-established methods. From the C–V curves, the built-in voltage and the base layer doping density for each subcell are calculated.

GaAsP/SiGe tandem solar cells on porous Si substrates

“…7, bottom inset). The detailed understanding of C-V curves in multijunction solar cells is not straightforward, since only the voltage across the device terminals is known and no information is available about the particular bias at each subcell (Ruiz et al 2010, Rutzinger et al 2017, Hoheisel et al 2011. However, in this case we simply intend to detect the signature of a parasitic diode in reverse bias.…”

Transient analysis of luminescent coupling effects in multi-junction solar cells

“…Here, we assume for simplicity time-and intensity-independent values for the capacitance C. In addition, to reproduce the transient V oc under medium light intensities as well as possible, we used a fixed value of 100 nF while the capacitance is typically around 100 nF/cm 2 and depends on the applied voltage and light intensity. 33,41 The LC efficiencies are set to 0.1 for the coupling from both J3-to-J2 and J2-to-J1 (α 32 = α 21 = 0.1) while coupling from J3-to-J1 was set to zero. This is supported by the fact that the coupling efficiency from J3-to-J1 is estimated as α 31 ≈ α 21 × α 32 = 0.01 for the case of α 32 = α 21 = 0.1.…”

How to perform admittance spectroscopy and DLTS in multijunction solar cells

“…However, in MJSCs, the junctions and admittances of each subcell are electrically (and optically) coupled, so that the response of the MJSC to a change in electrical bias (either modulated or transient) has to be properly analysed in order to separate the contribution of each subcell. Interestingly, while MJSCs have become one of the main target in photovoltaics, only very few studies can be found in the literature that aim at developing methods to separate the admittance (and thus the capacitance) of each subcell from the measurement performed on the MJSC [32][33][34][35].…”