A low-cost and green-solvent-processable hole-transport material enabled by a traditional bidentate ligand for highly efficient inverted perovskite solar cells

Low-cost and eco-friendly hole-transport materials (HTMs) are exceedingly desirable for the practical application of perovskite solar cells (PVSCs). Here, a traditional bidentate ligand (1,10-phenanthroline), widely used as a chelating agent for bioorganic reagents and probes, is incorporated into an HTM to affordM1. Such a planar bidentate ligand at the central core of the HTM can facilitate π-π stacking and enable chelation to Pbion defects and thus achieve efficient passivation at theM1/perovskite interface, contributing to reduced recombination loss. When employed as an HTM in inverted PVSCs without dopants, bidentate-ligand-basedM1yields a high power conversion efficiency (PCE) of 20.14%, which is significantly higher than that (18.32%) of theM0analogue that contains phenanthrene. More importantly, green solvent processing (ethyl acetate) ofM1achieves a PCE of 19.21%, which is among the highest values reported in PVSCs with a green-solvent-processable HTM. Besides, the facile one-step synthesis route reduces the cost to 45 $ gramforM1, which is cheaper than the most reported HTMs for high-efficiency PVSCs without dopants. These findings demonstrate the potential of bidentate ligands in developing cost-effective and eco-friendly HTMs toward highly efficient PVSCs.