Multifunctional Biomolecules Bridging a Buried Interface for Efficient Perovskite Solar Cells

The inevitably positively and negatively charged defects on the SnO₂/perovskite buried interface often lead to nonradiative recombination of carriers and unfavorable alignment of energy levels in perovskite solar cells (PSCs). Interface engineering is a reliable strategy to manage charged defects. Herein, the nicotinamide adenine dinucleotide (NAD) molecules with multiple active groups of ─P=O, ─P-O, and ─NH₂ are introduced to bridge the SnO₂/perovskite buried interface for achieving simultaneous elimination of positively and negatively charged defects. We demonstrate that the ─P=O and ─P-O groups in NAD not only fix the uncoordinated Pb²⁺ but also fill the oxygen vacancies (V_O) on the SnO₂ layer to eliminate positively charged defects. Meanwhile, ─NH₂ groups form hydrogen bonds with PbI₂ to reduce the number of negatively charged defects. In addition, the NAD biomolecules as a bridge induce high perovskite crystallization and accelerated electronic transfer along with favorable energy band alignment between SnO₂ and perovskite. Finally, the PSCs with the ITO/SnO₂/NAD/Cs_0.15FA_0.75MA_0.1PbI₃/Spiro-OMeTAD/Ag structure deliver an improvement in the power conversion efficiency from 20.49 to 23.18% with an excellent open-circuit voltage (V_oc) of 1.175 V. This work demonstrates that interface engineering through multifunctional molecular bridges with various functional groups is an effective approach to improve the performance of PSCs by eliminating charged defects and simultaneously regulating energy level alignment.