Less-acidic boric acid-functionalized self-assembled monolayer for mitigating NiOx corrosion for efficient all-perovskite tandem solar cells

The interfacial contact between NiO_x and self-assembled monolayers (SAMs) in wide-bandgap (WBG) subcells limits the efficiency and stability of all-perovskite tandem solar cells (TSCs). The strongly acidic phosphoric acid (PA) anchors in common PA-SAMs corrode reactive NiO_x, undermining device stability. Moreover, SAM aggregation leads to interfacial losses and significant open-circuit voltage (V_OC) deficits. Here, we introduce boric acid (BA) as a milder anchoring group that chemisorbs onto NiO_x via strong - <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>BO</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:mstyle><mml:mtext>-</mml:mtext></mml:mstyle> </mml:math> -Ni coordination. A benzothiophene-fused head group enhances interfacial bonding through S-Ni orbital interactions, yielding higher binding energy than PA-SAMs. This design also promotes homogeneous SAM formation without aggregation. Resultantly, the WBG cell exhibits an improved PCE to 20.1%. When integrated with narrow bandgap (NBG) subcell, the two-terminal (2T) TSCs achieve an ameliorative PCE of 28.5% and maintain 90% of the initial PCE after maximum power point tracking (MPP) under 1 sun illumination for 500 h.