Slot-Die-Printed Two-Dimensional ZrS₃ Charge Transport Layer for Perovskite Light-Emitting Diodes

Liquid-phase exfoliation of zirconium trisulfide (ZrS₃) was used to produce stable and ready-to-use inks for solution-processed semiconductor thin-film deposition. Ribbon-like layered crystals of ZrS₃ were produced by the chemical vapor transport method and were then exfoliated in three different solvents: dimethylformamide, ethanol, and isopropyl alcohol. The resulting ZrS₃ dispersions were compared for stability and the ability to form continuous films on top of the perovskite layer in light-emitting diodes with the ITO/PEDOT:PSS/MAPbBr₃/2D-ZrS₃/LiF/Al structure. Film deposition was performed by using either spray or slot-die coating methods. The slot-die coating route proved to produce better and more uniform films with respect to spray coating. We found that the 2D ZrS₃ electron injection layer (EIL) stabilized the interface between the perovskite and LiF/Al cathode, reducing the turn-on voltage to 2.8 V and showing a luminance that does not degrade during voltage sweep. On the other hand, EIL-free devices show electroluminescence on the first voltage sweep that reduces almost to zero in the subsequent sweeps. Combining physical device simulation and density functional theory calculation, we are able to explain these results in terms of lowering the electron injection barrier at the cathode.