# Bulk and interface engineering of 1.7 eV–bandgap chalcogenide solar cells enabling record efficiency

## TL;DR

Researchers improved the efficiency of wide-bandgap chalcogenide solar cells by modifying their bulk and interface properties.

## Contribution

A new method combining Al alloying and Rb incorporation is introduced to enhance solar cell performance.

## Key findings

- Al and Rb modifications lead to distinct interfacial chemistry and structural properties.
- A steep Al concentration gradient boosts device performance with minimal Al content.
- Higher open-circuit voltage is achieved without reducing photovoltaic efficiency.

## Abstract

Wide-bandgap chalcogenide photovoltaics offer strong potential for tandem solar cells and solar-driven hydrogen generation via water splitting, yet their performance remains limited by persistent interfacial and bulk defects. Here, we demonstrate enhanced efficiency in 1.7–electron volt CuGaSe2 thin-film solar cells through aluminum (Al) alloying and rubidium (Rb) incorporation. The Al- and Rb-modified CuGaSe2 absorber exhibits fundamentally distinct interfacial chemistry, structural properties, and metastable defect behavior compared with conventional narrow-bandgap Cu (In,Ga)Se2 solar cells. Moreover, we demonstrate that introducing a steep Al concentration gradient to engineer a back-surface electric field is a highly effective means of boosting device performance, even at an Al content of approximately 1 atomic % or less. By integrating these strategies, we achieve a higher open-circuit voltage without compromising photovoltaic efficiency, establishing a performance benchmark for wide-bandgap (1.65 to 1.75 electron volts) chalcogenides. These findings highlight the unique characteristics of wide-bandgap chalcopyrites and suggest a promising pathway toward next-generation, high-efficiency photovoltaic technologies.

Bulk and interface engineering strategies are developed to improve the performance of wide-bandgap chalcogenide solar cells.