Efficiency Boost in Highly Flexible Cu(In, Ga)Se2 Solar Cells on Mica by One-Step Sputtering with Rear-Side Modification

This study presents a novel approach for developing flexible Cu(In, Ga)Se₂ (CIGS) solar cells on mica substrates. Leveraging mica's chemical inertness and high-temperature resistance, we employ a one-step sputtering deposition process to enable efficient solar cell fabrication. A strategically integrated 50 nm titanium nitride (TiN) layer serves as both an adhesion promoter and a critical enhancer of Mo crystallinity, promoting CIGS grain growth and significantly enhancing device efficiency. With the TiN layer, the device achieves 13.5% efficiency, representing a 2.7% point improvement over the reference sample. The rear-side modification using a TiN buffer layer enhances device performance by improving film adhesion to mica, increasing back electrode conductivity, promoting defect passivation through increased crystallinity and grain size, and lowering the backside barrier height. Mechanical stability tests confirm the exceptional resilience of CIGS solar cells on mica, retaining approximately 98% of their initial efficiency after 3000 bending cycles at a 5 mm curvature radius. This robustness is attributed to mica's distinctive layered structure with weak van der Waals bonding. These findings highlight the potential of mica substrates to advance flexible photovoltaics by overcoming limitations of metal or polymer-based substrates. Offering superior thermal stability and mechanical durability, mica paves the way for next-generation wearable solar technologies.