Atomic layer deposition of PbCl2, PbBr2 and mixed lead halide (Cl, Br, I) PbXnY2−n thin films

Abstract

Atomic layer deposition offers outstanding film uniformity and conformality on substrates with high aspect ratio features. These qualities are essential for mixed-halide perovskite films applied in tandem solar cells, transistors and light-emitting diodes. The optical and electronic properties of mixed-halide perovskites can be adjusted by adjusting the ratios of different halides. So far ALD is only capable of depositing iodine-based halide perovskites whereas other halide processes are lacking. We describe six new low temperature (≤100 °C) ALD processes for PbCl₂ and PbBr₂ that are crucial steps for the deposition of mixed-halide perovskites with ALD. Lead bis[bis(trimethylsilyl)amide]–GaCl₃ and –TiBr₄ processes yield the purest, crystalline, uniform and conformal films of PbCl₂ and PbBr₂ respectively. We show that these two processes in combination with a PbI₂ process from the literature deposit mixed lead halide films. The four less optimal processes revealed that reaction by-products in lead halide deposition processes may cause film etching or incorporate themselves into the film.