Homogenizing hole-selective contacts for centimeter-square flexible perovskite/Cu(In,Ga)Se₂ tandems

Area of Science:

• Materials Science
• Photovoltaics
• Organic Electronics

Background:

• Flexible perovskite/Cu(In,Ga)Se2 (CIGS) tandems are promising for high-efficiency, lightweight solar energy.
• Interfacial inhomogeneity from molecular aggregation in hole-selective contacts (HSCs) hinders performance and durability.
• Planar carbazole-based HSCs on flexible substrates exhibit aggregation issues.

Purpose of the Study:

• To overcome interfacial inhomogeneity in flexible perovskite/CIGS tandems.
• To enhance both power conversion efficiency (PCE) and mechanical robustness.
• To develop a molecular engineering strategy for improved HSCs.

Main Methods:

• Developed a spatial steric hindrance strategy to create 3D π-conjugated carbazole structures.
• Transformed planar carbazole cores into 3D skeletons to suppress intermolecular π-π stacking.
• Integrated these modified HSCs into flexible monolithic perovskite/CIGS tandem devices.

Main Results:

• Achieved a champion stabilized PCE of 26.2% (certified 25.5%) for small-area devices.
• Attained a 25.3% (certified 24.3%) PCE for centimeter-scale devices.
• Demonstrated remarkable mechanical robustness, retaining initial PCE after 10,000 bending cycles (10 mm radius).

Conclusions:

• Molecular-level interfacial engineering via 3D π-conjugated skeletons effectively homogenizes selective contacts.
• The strategy leads to high-quality perovskite films and superior device performance.
• This approach enables the development of high-efficiency, stable, and scalable flexible tandem photovoltaics.