Bisphosphonate Self‐Assembled Molecules Enhance Anchoring Strength and Perovskite Passivation Toward High‐Efficiency Perovskite/Silicon Tandem Solar Cells

Self-assembled molecules (SAMs) are widely employed in wide-bandgap perovskite sub-cells (WPSCs) for perovskite/silicon tandem solar cells (PSTSCs) due to their facile fabrication and efficient hole transport. However, the limited anchoring strength of the single phosphonic acid head group makes the SAM prone to hydrolytic desorption from the substrate, thereby compromising device stability. Meanwhile, interfacial energy losses at the SAM/perovskite interface, arising from buried interface defects, remain critical challenges for the performance of WPSCs. Accordingly, we introduce a novel zoledronic acid (ZDA) interfacial modifier incorporating bisphosphonic acid head groups, which provides strong anchoring stability to substrates, enables hydrogen bonding with the SAMs, and offers effective perovskite passivation. Simultaneously, the imidazole ring end group of ZDA can also interact with the perovskite, further modifying the SAM/perovskite interface properties. As a result, high-performance WPSCs were obtained, delivering a maximum power conversion efficiency (PCE) of 20.55% and retaining over 90% of their initial performance after 200 h of maximum power point (MPP) tracking. In combination with silicon sub-cells, the resulting PSTSCs achieved a PCE of 30.62% and maintaining 95% of their initial efficiency after 500 h of MPP tracking.