Frequency response of the external quantum efficiency in multijunction solar cells

Area of Science:

• Optoelectronics
• Solid State Physics
• Renewable Energy

Background:

• High-quality multijunction solar cells are crucial for efficient energy conversion.
• Understanding external quantum efficiency (EQE) frequency dependence is key to optimizing solar cell performance.
• Existing characterization methods may lack sensitivity to subtle subcell variations.

Purpose of the Study:

• To investigate the frequency dependence of external quantum efficiency (EQE) in multijunction solar cells.
• To identify unique spectral features sensitive to subcell parameters and light bias.
• To validate a proposed AC equivalent circuit model against experimental data.

Main Methods:

• Utilized modulated photocurrent spectroscopy with a light-pipe-coupled compact LED array.
• Employed sinusoidal electrical modulation of LEDs via a custom high-bandwidth amplifier.
• Analyzed amplitude and phase data from EQE frequency sweeps.

Main Results:

• Observed distinct features in EQE amplitude and phase frequency sweeps.
• Demonstrated high sensitivity of these features to subcell parameters.
• Showed significant sensitivity to varying light bias conditions.
• Achieved remarkable agreement between experimental data and the AC equivalent circuit model.

Conclusions:

• The modulated photocurrent spectroscopy method effectively reveals unique EQE frequency-dependent features.
• The proposed AC equivalent circuit model accurately describes the observed phenomena.
• This technique offers a powerful tool for characterizing and optimizing multijunction solar cells.