Direct evaluation of influence of electron damage on the subcell performance in triple-junction solar cells using photoluminescence decays

David M Tex,Yoshihiko Kanemitsu,Mitsuru Imaizumi,Takeshi Ohshima,Tetsuya Nakamura

doi:10.1038/s41598-017-02141-0

Abstract

Tandem solar cells are suited for space applications due to their high performance, but also have to be designed in such a way to minimize influence of degradation by the high energy particle flux in space. The analysis of the subcell performance is crucial to understand the device physics and achieve optimized designs of tandem solar cells. Here, the radiation-induced damage of inverted grown InGaP/GaAs/InGaAs triple-junction solar cells for various electron fluences are characterized using conventional current-voltage (I–V) measurements and time-resolved photoluminescence (PL). The conversion efficiencies of the entire device before and after damage are measured with I–V curves and compared with the efficiencies predicted from the time-resolved method. Using the time-resolved data the change in the carrier dynamics in the subcells can be discussed. Our optical method allows to predict the absolute electrical conversion efficiency of the device with an accuracy of better than 5%. While both InGaP and GaAs subcells suffered from significant material degradation, the performance loss of the total device can be completely ascribed to the damage in the GaAs subcell. This points out the importance of high internal electric fields at the operating point.

Highlights

The tandem solar cells utilize several junctions connected in series to achieve high conversion efficiencies[1,2,3]
We find that the recombination losses increased in both InGaP and GaAs subcells due to the electron irradiation
We find that the conversion efficiency of the entire device measured with I–V curves can be predicted with the time-resolved method with an accuracy of better than 5%

Summary

Introduction

The tandem solar cells utilize several junctions connected in series to achieve high conversion efficiencies[1,2,3]. Steady-state luminescence signals can be used to analyze the solar cells material quality[15,16,17], and time-resolved luminescence signals provide information on the current generation dynamics[10, 14]. Conversion efficiencies by observing physical parameters such as the drift time constant[18] By extending this technique to more devices with different device structures, further understanding of the influence of the radiation damage on the current generation dynamics can be gained. We measure the I–V curves and PL decays of InGaP and GaAs subcells in ten triple-junction solar cells before and after irradiation with electrons. Due to the high internal electric fields in the InGaP subcell, the material degradation of the InGaP subcell has only a weak influence on the entire device performance at the point of maximum power

Methods

Results

Conclusion