Internal luminescence efficiencies in InGaP/GaAs/Ge triple-junction solar cells evaluated from photoluminescence through optical coupling between subcells

Abstract

In-situ characterization is one of the most powerful techniques to improve material quality and device performance. Especially in view of highly efficient tandem solar cells this is an important issue for improving the cost-performance ratio. Optical techniques are suitable characterization methods, since they are non-destructing and contactless. In this work, we measured the power dependence of photoluminescence (PL) from the InGaP and GaAs subcells of an industry-standard triple-junction solar cell. High luminescence yields enhance the luminescence coupling, which was directly verified by time-resolved PL measurements. We present a new method to determine the internal luminescence efficiencies of InGaP and GaAs subcells with the aid of luminescence coupling. High luminescence efficiencies of 90% for GaAs and more than 20% for InGaP were found, which suggest that the material quality of the grown GaAs layer is excellent while the intrinsic luminescence limit of InGaP is still not reached even for high excitation conditions. The PL method is useful for probing the intrinsic material properties of the subcells in flat band condition, without influence of transport. Since no calibration of absolute PL is required, a fast screening of the material quality is possible, which should be extremely helpful for the solar cell industry.

Analyzing the Electrical Performance of a Solar Cell with Time-Resolved Photoluminescence: Methodology for Fast Optical Screening

“…Characterization of optoelectronic devices with photoluminescence (PL) is fast, highly sensitive, contactless, and non-destructive. It is useful since PL directly reflects the device quality [14][15][16][17]. With regard to the information about the carrier dynamics, the PL spectra easily allow for individual characterization of different subcells, which is essential for tandem solar cell engineering.…”

Experimental Determination of Power Losses and Heat Generation in Solar Cells for Photovoltaic-Thermal Applications

“…Considering photon recycling negligible can be a source of error in evaluating thermal losses especially in the case of stacked multi-junction solar cells [11][12][13]. However in this work we will show that radiative recombination accounts for a very small fraction of the whole loss (1-3%) showing how this assumption leads to marginal inaccuracies only.…”

Practical target values of Shockley–Read–Hall recombination rates in state‐of‐the‐art triple‐junction solar cells for realizing conversion efficiencies within 1% of the internal radiative limit

“…Characterization of luminescence from solar cells is useful for estimation of the internal energy loss. In particular, the external luminescence efficiency ( η ext ) and the internal luminescence efficiency ( η int ) can be used for the quantitative analysis of non‐radiative recombination losses in III–V solar cells: η ext is the ratio of photon flux exiting the cell to the total carrier recombination rate, and η int is the probability of radiative emission in a single electron–hole recombination event. Based on the detailed balance theory and the reciprocity relation between electroluminescence (EL) intensity and external quantum efficiency (EQE) spectrum, it has been shown that the quantitative current–voltage (J–V) characteristics and the voltage losses in each subcell of a MJ solar cell can be evaluated by using η ext .…”