We investigate the role of luminescence effects on the analysis of solar cell properties. InGaP/GaAs tandem solar cells fabricated using hydride vapor phase epitaxy have a luminescent coupling (LC) efficiency of 0.6% from the top to the bottom subcell. We investigate the impact of LC on subcell current–voltage curve analysis using electroluminescence (EL) measurements. EL efficiency measurements were performed using a reference InGaP single-junction device. It was found that the luminescence extraction from the top subcell, and therefore its luminescence collection efficiency, is lower than that from the bottom subcell. This is due to LC from the top subcell to the bottom subcell. By considering the luminescence extractions of each subcell, more reasonable subcell voltages than those found by conventional methods can be obtained.
In intermediate band solar cells (IBSCs), voltage preservation is a key issue to overcome efficiency limit in singlejunction solar cells. To achieve this, quasi-Fermi level splitting of respective transitions should be investigated because equivalent circuit model of an IBSC is series-parallel connected diodes. In this study, we have quantitatively investigated quasi-Fermi level splitting, Δμ in InAs quantum dot solar cells (QDSCs) by performing absolute intensity calibrated photoluminescence (PL) spectroscopy. Multi-stacked InAs/GaAs QDs were fabricated in the i-region of a GaAs p-i-n single-junction solar cell. QD ground states and GaAs band edge emissions were observed simultaneously by using a near-infrared sensitive CCD spectrometer. Excitation density dependence and temperature dependence were investigated in detail to clarify photo-carrier kinetics in QDSCs and tackle the voltage preservation issue on IBSCs. At room temperature, nonlinear increase in PL intensity was clearly observed at high excitation density above 1000 suns. Absolute PL spectra was analyzed at respective transitions by using generalized Plank’s law. As the result of detail analysis, increase in Δμ was confirmed at high excitation density and at room temperature, which suggested voltage recovering via photo-filling effect. It would be desirable to implement voltage preservation in IBSCs.
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