Local Voltage Mapping of Solar Cells in the Presence of Localized Radiative Defects | JoVE Visualize

Area of Science:

Materials Science
Photovoltaics
Spectroscopy

Background:

Hyperspectral imaging provides 3D luminescence data for photovoltaic materials, enabling voltage mapping via quasi-Fermi-level splitting.
Extraction of accurate voltage maps requires supplemental external quantum efficiency (EQE) measurements, which often lack spatial resolution.
Previous methods relied on assumptions to reconcile differing spatial resolutions between luminescence and EQE data.

Purpose of the Study:

To evaluate the validity of existing assumptions for voltage extraction in InGaAs solar cells with spatially varying luminescence spectra.
To identify the impact of significant spectral variations, caused by radiative defects, on the accuracy of extracted voltage and EQE maps.
To propose improved methods for accurate voltage mapping in complex photovoltaic devices.

Main Methods:

Utilized hyperspectral electroluminescence and photoluminescence imaging to acquire spatially and spectrally resolved luminescence data.
Performed supplemental external quantum efficiency (EQE) measurements.
Evaluated the accuracy of voltage and EQE extraction under conditions of significant spatial variation in luminescence spectral shape.

Main Results:

Found that assumptions used to overcome spatial resolution differences can lead to non-physical external quantum efficiencies (EQEs) and underestimated voltages.
Demonstrated that these inaccuracies are pronounced in InGaAs solar cells with significant spatial variations in luminescence spectral shape due to radiative defects.
Identified that existing assumptions are only appropriate for minor variations in spectral shape.

Conclusions:

The study highlights the limitations of current assumptions in hyperspectral imaging for accurate voltage mapping in photovoltaic devices with spectral heterogeneity.
Combining multiple analysis methods or extracting a minimum voltage map can mitigate errors, especially when external quantum efficiency (EQE) is high.
Accurate characterization of photovoltaic materials with complex defect distributions requires refined data processing techniques.