Abstract
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.
Highlights
Luminescence properties are very important to consider in the fabrication and characterization of high-efficiency solar cells.[1,2] Photon recycling has greatly improved the conversion efficiency of thin GaAs solar cells.[3,4] Multijunction solar cells contain very high-quality materials that exhibit extremely high conversion efficiency and strong luminescent coupling (LC) between the junctions
The presence of LC has a significant impact on the behavior of multijunction solar cells, affecting the optimal design of these devices and the characterization of the solar cell
LC is regarded as a particular case of photon recycling in which luminescence from radiative recombination in a higher-bandgap subcell is reabsorbed by the lower-bandgap subcells, increasing the photocurrent in them
Summary
Luminescence properties are very important to consider in the fabrication and characterization of high-efficiency solar cells.[1,2] Photon recycling has greatly improved the conversion efficiency of thin GaAs solar cells.[3,4] Multijunction solar cells contain very high-quality materials that exhibit extremely high conversion efficiency and strong luminescent coupling (LC) between the junctions. LC can overcome the limitations on the current in a series-connected multijunction solar cell caused by lower-bandgap subcells and can increase the current in the entire device. This makes it possible to compensate for current mismatch under spectral mismatch conditions.[9]. In EL measurements of multijunction devices with efficient LC, applying a forwardbias voltage to the device results in luminescence that generates additional photocurrent in the adjacent lower subcell; this prevents precise characterization of the subcell voltages.[23] investigating subcell Voc is complicated by the LC effect and requires multiple measurements and model analysis.[10,23]. The subcell voltage obtained by our model is compared with that estimated by conventional methods
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