Dual-Side Engineered Bilayer Molybdenum for Flexible Monolithic Perovskite/ Cu(In,Ga)Se2 Tandem Solar Cells on Polyimide

Abstract Flexible monolithic perovskite/Cu(In,Ga)Se2 (CIGS) tandem solar cells (TSCs) on polyimide (PI) substrates suffer from severe interfacial delamination and compromised CIGS crystallization induced by back-contact thermal limitations. Herein, we introduce a dual-side engineered bilayer molybdenum (DEBM) architecture to mitigate these challenges. The loose surface layer of DEBM enhances selenium diffusion to secure robust adhesion, while the backside Mo microstructure modulates infrared reflectivity for efficient thermal management. This synergistic regulation improves CIGS crystallization and suppresses defects. Consequently, single-junction flexible CIGS cells eliminate cracking and delamination, achieving a > 20.0% certified efficiency. The integrated monolithic TSCs deliver a champion efficiency of 27.03% (certified 26.30%), the highest efficiency reported to date for PI-based TSCs. The device also exhibits outstanding bending durability, retaining over 96% of initial performance after 20,000 bending cycles at a 5 mm radius. This architecture provides a viable pathway for highly reliable, flexible tandem photovoltaics.