Loss analysis of Low Bandgap (Ag,Cu)(In,Ga)Se2 Solar Cells for Tandem Applications

TL;DR

This paper provides a comprehensive loss analysis of 1.0 eV bandgap (Ag,Cu)(In,Ga)Se2 solar cells, identifying key efficiency losses and their causes, with implications for tandem solar cell development.

Contribution

It offers the first detailed loss analysis of these specific chalcopyrite solar cells, highlighting the dominant voltage and fill factor losses.

Findings

Major voltage losses due to non-radiative recombination in the absorber.

Fill factor losses linked to high diode factor and recombination in the space charge region.

Absorption losses in the absorber can only be reduced with light management structures.

Abstract

Tandem solar cells can better harness the energy of the solar spectrum. Chalcopyrite solar cells have drawn attention, being the only highly efficient devices with bandgap around 1.0 eV, suitable for bottom cells. In the quest for better efficiencies, we conduct a complete loss analysis of 1.0 eV bandgap (Ag,Cu)(In,Ga)Se2 cells with efficiencies around 18.5%. We perform absolute photoluminescence, electroluminescence, JV and EQE measurements on the absorber and the finished cells to analyze losses of short-circuit current, open-circuit voltage and fill factor. The relevant losses in current are due to absorption losses in the absorber and could only be mitigated by light management structures. But the most significant losses are found in the voltage, due to non-radiative recombination in the absorber, and the fill factor, due to a high diode factor. The diode factor of the cells is significantly higher than in the absorber alone, indicating a strong influence of recombination in the space charge region.