Strong performance enhancement in lead-halide perovskite solar cells through rapid, atmospheric deposition of n-type buffer layer oxides

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) films with the requisite thickness in 2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown directly on the perovskite, there is also minimal structural damage to the underlying perovskite layer. The SnOx layer is pinhole-free and conformal. When used to cover perovskite devices with a PC61BM electron transport layer, shunting due to the pinholes in the spin-coated PC61BM is reduced, resulting in increases in the steady-state efficiency 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. Pinhole-free TiO2 and SnO2 films are grown within minutes under atmospheric conditions from the vapor-phase onto lead-halide perovskite/PC61BM, improving photovoltaic performance through reduced shunting in the electron transport layer. The short processing times allows oxides to be grown at ≥180 °C onto the perovskite device stack, which is ≥ 70 °C larger than achievable by current methods. Oxides grown at higher temperature are more conductive, resulting in higher efficiencies. [Display omitted] •Vapor-based technique demonstrated for growing pinhole-free oxide buffer layers in open-air orders of magnitude faster than existing vacuum-based methods.•Rapid deposition allows TiO2 to be grown at up to 180 °C on thermally-unstable lead-halide perovskites.•Higher growth temperatures result in less resistive TiO2 films, boosting absolute perovskite solar cell efficiencies by >2%.•Technique also demonstrated for SnO2, and perovskite solar cells with dense SnO2 overlayer improve