DMF passivating perovskite/PCBM interface for high-efficiency and stable inverted perovskite solar cells

A major unresolved challenge in inverted organic-inorganic hybrid perovskite solar cells (I-PSCs) is interfacial non-radiative recombination. To tackle this issue, we introduced trace dimethylformamide (tDMF) in isopropanol (tDMF/IPA) as a passivation material, carefully modifying the interface between FA0.95Cs0.05PbI3 and [6,6]-phenyl-C61-butyric acid methyl ester. The experimental results of energy dispersive X-ray spectroscopy at different voltages and angles, infrared spectroscopy, and X-ray photoelectron spectroscopy indicate that oxygen lone pair of electrons in carbonyl group (-C=O) of polar solvent N,N-dimethylformamide form coordination bonds (Pb2+ → O=C) with Pb²⁺ suspension bond on the surface of perovskite. Tafel polarization curve and dark current results reveal decrease in the charge recombination rate at the interface and decrease in leakage current, respectively, after tDMF/IPA passivation. The photoelectric conversion efficiency (PCE) of I-PSCs treated with tDMF/IPA is significantly increased from 21.44% to 23.24%, and the open-circuit voltage is also increased from 1.01 to 1.12 V. Encapsulated devices based on tDMF/IPA passivation retained over 77% of their initial PCE after being stored in ambient air for 2,736 h.