Dipolar-Steric Cage Diammonium Passivation for Perovskite/Tunnel Oxide Passivated Contact Tandem Solar Cells

Resolving the long-standing trade-off between effective interfacial passivation and efficient charge transport remains a central challenge for perovskite/silicon tandem solar cells, particularly at the perovskite/C60 interface. Here, inspired by the bio-isostere concept, we introduce a dipolar cage strategy that replaces traditional planar phenyl motifs with a rigid bicyclo[2.2.2]octane (BCO) scaffold. Distinct from conventional passivators relying solely on steric shielding, the BCO framework imparts a substantial intrinsic molecular dipole. This architecture establishes a favorable interfacial electrostatic field, substantially reducing the interfacial energetic mismatch for electron extraction while effectively suppressing nonradiative recombination. Utilizing bicyclo[2.2.2]octane-1,4-diammonium diiodide (BCODAI), monolithic perovskite/tunnel oxide passivated contact (TOPCon) tandem solar cells achieve a certified champion efficiency of 32.54%. Crucially, the devices exhibit outstanding operational stability, retaining over 80% of their initial efficiency after 1100 h of continuous operation. This dipolar-steric cage design provides an effective interfacial engineering principle for high-performance tandem photovoltaics.