Polar heterocyclic molecule-assisted co-assembly of monolayers at the NiOx/perovskite interface for high-efficiency and stable inverted perovskite solar cells

Abstract

Self-assembled monolayers (SAMs) are capable of improving the quality of perovskites and passivating defects, but their inhomogeneous layer formation hinders molecular connectivity and charge transport. To address these issues, a heteroarene molecule (benzo[c][1,2,5]oxadiazoe-5-boronic acid, BBOA) is chosen to form a co-assembled (Co-SAM) layer with MeO-2PACz to increase the coverage and reduce inherent defects of the Co-SAM layer on NiO_x through π–π stacking interactions. Meanwhile, BBOA can form Pb–O bonds and O–H⋯I⁻ hydrogen bonds with the defects from the perovskite. Besides, the strong electron-withdrawing oxadiazole functionality deepens the molecular energy levels and redistributes the electronic environment, thereby optimizing the energy level alignment and charge extraction at the interface. As a result, the BBOA-modified perovskite solar cells achieved a champion efficiency of 25.08%, which is superior to that of the NiO_x/MeO-2PACz-based device (23.62%), and maintained 93.4% and 87.4% of its initial performance after 1200 hours at 25 °C and after 672 hours at 65 °C, respectively, under an N₂ atmosphere during continuous operation without encapsulation.