Conversion efficiency limits and bandgap designs for multi-junction solar cells with internal radiative efficiencies...

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Multi-junction solar cells offer high conversion efficiencies.
• Realistic material properties, such as internal radiative efficiency (ηint), impact theoretical limits.
• The role of intermediate reflectors in multi-junction solar cells requires further investigation.

Purpose of the Study:

• To calculate the conversion-efficiency limit (ηsc) for 1-5 junction solar cells.
• To determine optimized subcell bandgap energies under various irradiation conditions.
• To assess the impact of internal radiative efficiency (ηint) and intermediate reflectors on ηsc.

Main Methods:

• Utilized an extended detailed-balance theory.
• Calculated ηsc and bandgap energies for 1-5 junction solar cells.
• Simulated performance under 1-sun AM1.5G and 1000-sun AM1.5D irradiations, with and without intermediate reflectors, considering varying ηint.

Main Results:

• ηsc significantly drops as the geometric mean of subcell ηint (ηint*) decreases from 1 to 0.1.
• ηsc degrades linearly with log(ηint*) for ηint* below 0.1.
• The benefit of intermediate reflectors diminishes for ηint* < 0.1 in optically thick cells.

Conclusions:

• Internal radiative efficiency is a critical factor limiting multi-junction solar cell performance.
• Optimized bandgap energies are influenced by decreasing ηint* and solar spectral characteristics.
• The study provides realistic efficiency targets and design guidelines for advanced solar cell development.