Rational design of self-assembled monolayer composition for efficient perovskite/Si tandem solar cells

Efficient charge extraction at the interface is essential for achieving high-performance perovskite/Si tandem solar cells. Here, we demonstrate a highly efficient wide-bandgap perovskite single-junction solar cell using a co-adsorption strategy of commercial self-assembled monolayers (SAMs), specifically MeO-4PACz and Br-4PACz. Mixed-SAMs, with electron-withdrawing Br functional groups, induce a larger dipole moment and a downward shift in the HOMO level, thereby promoting favorable energy level alignment with a wide-bandgap perovskite. It further passivates interfacial defects, suppressing non-radiative recombination. This combined effect enables effective hole transport at the SAM/perovskite interface, enhancing the open-circuit voltage and fill factor of the perovskite device. Accordingly, the optimal single-junction perovskite solar cell exhibits an efficiency of 19.72%. By integrating this cell with a Si bottom cell, we achieve a tandem solar cell efficiency of 28.02%. This study provides a universal strategy to design SAM-based interfacial layers in p-i-n perovskite and tandem solar cells.