Steric‐Complementary Synergistic Strategy for High‐Efficiency Monolithic Perovskite/Silicon Tandem Solar Cells

Abstract Achieving efficiencies beyond 40% with perovskite/silicon tandems hinges on conquering the challenge of interfacial recombination without inducing deleterious trade‐offs in charge extraction or stability. Herein, a steric‐complementary synergistic strategy (SCSS) is introduced that resolves this dilemma using a molecular dyad of piperazine (Pip ⁺ ) and phenethyl ammonium (PEA ⁺ ) cations. It is demonstrated that the compact Pip ⁺ cation infiltrates and neutralizes deep‐level surface defects inaccessible to larger molecules, while its bulkier PEA ⁺ counterpart co‐assembles into a robust, hydrophobic canopy that shields the interface from environmental stressors. This cooperative architecture synergistically suppresses trap‐state density and mitigates resistive losses, simultaneously enhancing charge extraction and device stability. Consequently, the tandem devices achieve a certified power conversion efficiency (PCE) of 32.12%. These tandems also exhibit exceptional operational stability, retaining over 80% of their initial efficiency after 1000 h of continuous one sun illumination under maximum power point tracking. This work establishes that engineering interfaces with sterically mismatched, functionally complementary molecules is a potent strategy, providing a clear pathway toward next‐generation tandem photovoltaics that are both highly efficient and truly durable.