Highly Planar Benzodipyrrole-Based Hole Transporting Materials with Passivation Effect for Efficient Perovskite Solar Cells

Three benzodipyrrole (BDP)-based organic small molecules with substituted 4-methoxyphenyl (CB-1), 3-fluorophenyl (CB-2), and 3-trifluoromethylphenyl (CB-3) are designed, synthesized, and used as a hole-transporting material (HTM) for perovskite solar cells (PSCs). The electrochemical, optical, thermal, electronic, and optoelectronic properties of the HTMs are characterized to verify their suitability for PSCs. The terminal functional groups of the HTMs having different heteroatoms mainly target effective defect passivation of perovskites. Photoluminescence studies and molecular dynamic simulations reveal that fluorine atoms within CB-2 and CB-3 can contribute to the defect passivation via interaction with Pb of the perovskite. In particular, a highly planar conformation of CB-2 on the perovskite surface can facilitate more efficient hole transfer at the interface. Thus, the PSCs employing CB-2 achieve the highest power conversion efficiency (PCE) of 18.23% while the devices using CB-1 and CB-3 exhibit a lower PCE of 16.78% and 16.74%, respectively. PSCs with the BDP-based HTMs demonstrate excellent long-term storage stability without degradation in their PCEs over 6 months. The highly planar geometry, defect passivation effect, and hydrophobicity of CB-2 show its great potential as an HTM for efficient and stable PSCs.