(Graph Presented) A new method to deposit perovskite thin films that benefit from the thickness control and conformality of atomic layer deposition (ALD) is detailed. A seed layer of ALD PbS is place-exchanged with PbI₂ and subsequently CH₃NH₃PbI₃ perovskite. These films show promising optical properties, with gain coefficients of 3200 ± 830 cm^-1.