Efficiency Enhancement with the Ferroelectric Coupling Effect Using P(VDF-TrFE) in CH₃NH₃PbI₃ Solar Cells

A novel ferroelectric coupling photovoltaic effect is reported to enhance the open-circuit voltage (V _OC) and the efficiency of CH₃NH₃PbI₃ perovskite solar cells. A theoretical analysis demonstrates that this ferroelectric coupling effect can effectively promote charge extraction as well as suppress combination loss for an increased minority carrier lifetime. In this study, a ferroelectric polymer P(VDF-TrFE) is introduced to the absorber layer in solar cells with a proper cocrystalline process. Piezoresponse force microscopy (PFM) is used to confirm that the P(VDF-TrFE):CH₃NH₃PbI₃ mixed thin films possess ferroelectricity, while the pure CH₃NH₃PbI₃ films have no obvious PFM response. Additionally, with the applied external bias voltages on the ferroelectric films, the devices begin to show tunable photovoltaic performance, as expected for the polarization in the poling process. Furthermore, it is shown that through the ferroelectric coupled effect, the efficiency of the CH₃NH₃PbI₃-based perovskite photovoltaic devices is enhanced by about 30%, from 13.4% to 17.3%. And the open-circuit voltages (V _OC) reach 1.17 from 1.08 V, which is reported to be among the highest V _OCs for CH₃NH₃PbI₃-based devices. It should be noted in particular that the thickness of the layer is less than 160 nm, which can be regarded as semi-transparent.