Engineering bonding sites enables uniform and robust self-assembled monolayer for stable perovskite solar cells

The efficiency of perovskite solar cells has recently been dramatically improved by a self-assembled monolayer (SAM), but forming uniform, dense and especially stable SAM remains a challenge. The hydroxyl groups on indium tin oxide (ITO) serve as the bonding sites for the SAM molecule, directly determining the distribution and anchoring stability of SAM. We developed a solution-based strategy to fully hydroxylate the ITO in as fast as 15 s. Moreover, further hydroxylation etching could also create abundant uncoordinated indium ions on the new exposed ITO surface for the anchoring of SAM by forming coordination bonds. In addition, the rapid hydroxylation etching allows commercial ITO to be directly used to omit the conventional multistep ITO pretreatment. Moreover, hydroxylation etching can also spontaneously form nano-antireflective structures on ITO to improve photon transmission. The versatile bonding site engineering resulted in better SAM anchoring, which delivered efficient perovskite solar cells (power conversion efficiency, 26.6%) that only lose 4% of the initial efficiency after 2,800 h of operation at 65 °C (ISOS-L-2 protocol).