HZB, Humboldt Hit 25.5% CIGS-Perovskite Tandem Record

• CIGSe–perovskite tandem solar cells hit a new 25.5% efficiency record—certified by Fraunhofer ISE—surpassing last year’s 24.6% benchmark through smarter bandgap and interface engineering.

Researchers at Humboldt University of Berlin and Helmholtz-Zentrum Berlin (HZB) have set a new efficiency record for a CIGSe–perovskite tandem solar cell at 25.5%. The device, slightly larger than 1 cm², beats the team’s prior 24.6% benchmark from last year for the same material system.

The result was independently certified by Fraunhofer ISE and added to the Solar Cell Efficiency Tables (“Green Tables”) as a global benchmark. Improvements came from optimizing tandem architecture, including varying CIGSe band gaps and using two aluminum-doped zinc oxide thicknesses. Interface engineering further reduced losses and boosted stability via nickel oxide and self-assembled monolayers, alongside electron-selective contact optimization.

What enabled Humboldt/HZB’s record 25.5% CIGSe–perovskite tandem solar cell?

• Bandgap engineering across the two subcells to better match the solar spectrum and improve how much light each layer can convert
  
• Precise control of the CIGSe absorber quality (e.g., defect density, crystallinity, and absorber stoichiometry) to raise voltage and reduce recombination losses
  
• Optimized perovskite formulation and processing to form a highly uniform film with fewer non-radiative recombination centers
  
• Advanced interface passivation at the perovskite/charge-transport and CIGSe/charge-transport contacts to suppress interfacial recombination
  
• Tailored charge-transport layer properties (electron- and hole-selecting behavior) to improve carrier selectivity and minimize resistive and parasitic losses
  
• Careful optical management to limit reflection and parasitic absorption while maximizing light harvesting in both subcells
  
• Minimization of series resistance through contact engineering and improved film/conduction-layer integration
  
• Suppression of moisture/oxygen sensitivity and enhancement of operational robustness through improved interfacial chemistry and device encapsulation strategies
  
• Use of materials and layers designed to maintain performance during processing steps (thermal/solvent compatibility) and subsequent handling
  
• Cell fabrication and integration steps tuned to ensure uniform current matching between the subcells (critical for tandem operation)
• Process reproducibility and yield-focused quality control (thickness uniformity, layer-to-layer alignment, and defect screening) to consistently reach high fill factors and voltages