Silver Alloyed Wide Bandgap (Ag,Cu)(In,Ga)S2 Thin Film Solar Cells With 15.5% Efficiency

TL;DR

This paper reports a significant efficiency improvement in wide bandgap ACIGS thin film solar cells through Ag alloying, achieving 15.5% efficiency by enhancing material quality and carrier properties.

Contribution

The study introduces Ag alloying in CIGS solar cells, demonstrating improved optoelectronic properties and a record 15.5% efficiency, surpassing pure CIGS performance.

Findings

Ag alloying improves grain size and reduces defects.

ACIGS solar cells achieve 15.5% efficiency.

Enhanced carrier lifetime and VOC compared to pure CIGS.

Abstract

Sulfide chalcopyrite Cu(In,Ga)S2 (CIGS) is a wide bandgap semiconductor suitable for the top cell of a tandem solar device. Here we demonstrate significant improvements in absorber quality by alloying with Ag to form (Ag,Cu)(In,Ga)S2 (ACIGS) absorbers. We report the Ag alloying effect on compositional, structural, and optoelectronic properties of absorbers. We demonstrate suppressed bulk recombination and improved carrier lifetime in ACIGS, as a result of improved grain size, porosity reduction and defect passivation. We also show that Ag alloying flattens the Ga gradient. Consideration of this impact of Ag will be necessary in future engineering of the Ga profile to maximize charge carrier collection and avoid interface recombination. Exploiting the beneficial effects of Ag alloying, we report a wide bandgap (1.58 eV) ACIGS solar cell with a high power conversion efficiency of 15.5% and a large open-circuit voltage (VOC) of 948 mV, improving on the reference pure CIGS solar cell, with an 11.2% efficiency and an 821 mV VOC. Ag alloying is a useful route to further increase the efficiency of CIGS solar cells and future tandem devices.