  Thin (approximately 10 nm) oxide buffer layers grown over lead-halide
perovskite device stacks are critical for protecting the perovskite against
mechanical and environmental damage. However, the limited perovskite stability
restricts the processing methods and temperatures (<=110 C) that can be used to
deposit the oxide overlayers, with the latter limiting the electronic
properties of the oxides achievable. In this work, we demonstrate an
alternative to existing methods that can grow pinhole-free TiOx (x =
2.00+/-0.05) films with the requisite thickness in <1 min without vacuum. This
technique is atmospheric pressure chemical vapor deposition (AP-CVD). The rapid
but soft deposition enables growth temperatures of >=180 {\deg}C to be used to
coat the perovskite. This is >=70 {\deg}C higher than achievable by current
methods and results in more conductive TiOx films, boosting solar cell
efficiencies by >2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown on
perovskites, there is also minimal damage to the perovskite beneath. The SnOx
layer is pinhole-free and conformal, which reduces shunting in devices, and
increases steady-state efficiencies from 16.5% (no SnOx) to 19.4% (60 nm SnOx),
with fill factors reaching 84%. This work shows AP-CVD to be a versatile
technique for growing oxides on thermally-sensitive materials.
