Atomic layer deposition of PbCl 2 , PbBr 2 and mixed lead halide (Cl, Br, I) PbX n Y 2- n thin films.

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 PbCl 2 and PbBr 2 that are crucial steps for the deposition of mixed-halide perovskites with ALD. Lead bis[bis(trimethylsilyl)amide]-GaCl 3 and -TiBr 4 processes yield the purest, crystalline, uniform and conformal films of PbCl 2 and PbBr 2 respectively. We show that these two processes in combination with a PbI 2 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.