Adjusting Nucleation Chemistry for the Atomic Layer Deposition of Antimony Selenide on Metal Oxide Surfaces

Mixed antimony chalcogenides (Sb 2 E 3 , E = S, Se) as solar light absorbers offer bandgap tunability with favorable optical and electrical properties. However, depositing continuous films of thickness adjusted to the high optical absorption coefficients (<100 nm) has been challenging due to the favored formation of crystalline needles. Atomic layer deposition (ALD) as an ideally conformal deposition method is suited to addressing this challenge, but in the case of Sb 2 Se 3 , nucleation chemistry effects can render the substrate inert. Using tris(dimethylamido)antimony (Sb(NMe 2 ) 3 ) and bis(trimethylsilyl)selenide ((Me 3 Si) 2 Se) as precursors, we demonstrate that undesirable silylation of surface hydroxyl groups can be minimized by a pretreatment with Sb(NMe 2 ) 3 . The near‐saturation of nucleation sites on a metal oxide surface is demonstrated by scanning transmission electron microscopy and X‐ray reflectometry. Density functional theory highlights the importance of thermodynamics for surface inhibition and reactivation. The insight gained is applied to establishing a Sb 2 Se 3 ALD process which delivers smooth, continuous, ultrathin (<50 nm) films even after thermal annealing and crystallization. Such films are successfully incorporated into functional solar cells. Unraveling the details of nucleation chemistry for the specific case of Sb 2 Se 3 ALD also provides a perspective on adjusting chemical bonding at the interface between an oxide and a heavier chalcogenide.