PVDF-HFP additive for visible-light-semitransparent perovskite films yielding enhanced photovoltaic performance

•A PVDF-HFP additive specific to semitransparent perovskite films was developed.•The additive has significant effects on perovskite-film-morphology control.•The additive improves carrier lifetimes and decreases charge transport resistance.•The additive achieves over 30% PCE enhancement compared to control devices.

Organometallic halide perovskite solar cells have considerable potential to be manufactured as low-cost and visible-light-semitransparent modules by reducing the thickness of the perovskite films for building-integrated photovoltaics. However, perovskite films often suffer from voids and roughness, inducing depressed photovoltaic performance, and this problem is even more severe for thinner perovskite films. Herein, a poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) additive is incorporated into CH3NH3PbI3 precursor solutions to control the crystal growth of a visible-light-semitransparent perovskite layer (thickness: ~150 nm) in a one-step deposition process. The characterization results show that the coverage and smoothness of the perovskite films can be significantly improved, and the perovskite crystal boundaries are also reduced by introducing a moderate amount of PVDF-HFP. When the precursor solution containing 12 mg/mL PVDF-HFP, the highest power conversion efficiencies of 10.6% and 8.8% (backward scan) is achieved for the photovoltaic devices with 80 and 20 nm-thick Au electrode, respectively, which is over 30% higher than that of the PVDF-HFP-free control. Time-resolved photoluminescence and electrochemical impedance spectroscopy characterizations further demonstrate that the PVDF-HFP additive can improve the carrier lifetimes and reduce the charge transfer resistance, which contributes to the enhanced photovoltaic performance. Thus, we propose a strategy specific to a high-quality visible-light-semitransparent perovskite layer and for high-performance perovskite solar-cell preparation.

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