Polar side-chain tuning of perylene diimide and fluorene-based cathode interfacial material for high-performance inverted perovskite solar cells

Cathode interface layers (CILs) play an important role in inverted perovskite solar cells (PVSCs) to correct the mismatched energy levels, improve electron extraction, and passivate interfacial defects. Herein, we reported a perylene diimide (PDI) and fluorene-based CIL material 2PDINT-FN with four dimethylamino functional side chains for highly efficient inverted PVSCs. The dimethylamino groups in both PDI and fluorene side chains endow 2PDINT-FN with high electrical conductivity, electron mobility, strong self-doping and interfacial dipole properties, which were further enhanced by adding N-DMBI as the dopant. The inverted PVSCs with 2PDINT-FN as a CIL showed a promising power conversion efficiency (PCE) of 20.03%, which was further improved to 21.85% with a simultaneously enhanced current density (J_sc) and fill factor (FF) after adding the N-DMBI dopant. A detailed analysis indicates that the defect density and charge recombination at the interface can be reduced effectively after adding the 2PDINT-FN CIL, leading to an improvement of charge collection and extraction efficiency.