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A variety of metal fluorides, including lithium fluoride (LiF), magnesium fluoride (MgF 2 ), barium fluoride (BaF 2 ), strontium fluoride (SrF 2 ), aluminum fluoride (AlF 3 ), zirconium fluoride (ZrF 4 ), and cerium fluoride (CeF 3 ), are used as the cathode interfacial layer (CIL) in polymer photovoltaic cells to assess their effect on device performance. CeF 3 , BaF 2 , and SrF 2 CILs exhibit better performance than a typical LiF CIL. The SrF 2 ‐based device shows a power conversion efficiency (PCE) of 7.17%, which is approximately 9% higher than that of the LiF‐based device; this, to our knowledge, is the first report on the SrF 2 ‐based organic photovoltaic cell device. The open‐circuit voltage ( V OC ) and fill factor (FF) of the fluoride‐based devices are correlated to the work functions (WFs) of the corresponding metals, which in turn influence the PCE. X‐ray photoelectron spectroscopy measurements of fluoride‐based cathodes reveal the occurrence of a displacement reaction and an interfacial dipole at the fluoride/aluminum interface, which lead to a reduced effective WF of the cathode and improved charge collection. Consequently, an improved PCE is achieved together with an increased V OC and FF.
Lin et al. (Tue,) studied this question.