Break | AIChE


Halide perovskites constitute a novel class of materials that possesses desirable properties for solar cell absorber layers and enables low-cost, high-throughput solution processing due to unique bulk defect tolerance. Despite the benign nature of bulk defects, surface-level defects that arise at grain boundaries and interfaces contribute to reduced device performance and stability. Passivation is a common approach to mitigating surface defects in halide perovskites through the addition of chemical species that strongly bond to perovskite surfaces to eliminate trap states and increase chemical integrity. In this regard, recent literature has shown alkali fluoride additives to be effective passivating agents for methylammonium lead iodide perovskites when added in minute quantities. Here we report the lamination and encapsulation of methylammonium lead iodide perovskite films using homo- and co-polymers of polyvinylidene fluoride as a source of passivating fluoride ions. Lamination is performed by pressing glass superstrates into polymer films over perovskite-coated glass substrates at elevated pressures and temperatures. We demonstrate that, with sufficient temperature, fluorine is released from the polymers and transferred as ionic fluoride to the perovskite surface. Under moderate processing conditions, this leads to four-fold carrier lifetimes compared to control samples. At more extreme conditions, we show that PbF2 is formed and acts as an electron acceptor, quenching carriers in the perovskite. After demonstrating passivating effect of fluoropolymer lamination, this research then focuses on the effective differences of multiple polyvinylidene fluoride co-polymers and their passivating activity under short lamination times and different temperature thresholds. These results suggest that Poly(vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene) [P(VDF-HFP-TFE)] reproduces carrier lifetimes with four-fold increase over control samples in lower temperature regimes (120 - 150 °C) while P(VDF-HFP) requires medium temperature ranges (150 - 180 °C). Research on short lamination times is important for future high throughput production of full halide perovskite solar cells as polymer layers may be added via rapid lamination to passivate and encapsulate halide perovskite films.