# Combined photo- and electroreflectance of multijunction solar cells enabled by subcell electric coupling

## TL;DR

This paper introduces a novel spectroscopy method combining photo- and electroreflectance to analyze individual subcells in multijunction solar cells by leveraging their electric coupling, enabling detailed device diagnostics.

## Contribution

It presents a new technique that allows simultaneous, independent characterization of subcells in a multijunction solar cell using combined photo- and electroreflectance spectroscopy.

## Key findings

- Successful demonstration on a GaInP/GaAs tandem solar cell.
- Ability to diagnose subcells individually within a monolithic device.
- Spectral separation enables targeted subcell analysis.

## Abstract

Electric coupling between subcells of a monolithically grown multijunction solar cell in short circuit allows their simultaneous and independent characterization by means of photo- and electroreflectance. The photovoltage generated by selective absorption of the pump beam in a given subcell during photoreflectance measurements results in reverse biasing the complementary subunits at the modulation frequency set on the pump illumination. Such voltage bias modulation acts then as external perturbation on the complementary subcells. The spectral separation of the different subcell absorption ranges permits the probe beam to record in a single spectrum the response of the complete device as a combination of photo- and electroreflectance, thereby providing access for diagnosis of subcells on an individual basis. This form of modulation spectroscopy is demonstrated on a GaInP/GaAs tandem solar cell.