PM Distinguished Seminar: Spatial Atomic Layer Deposition for Perovskite-Based Tandem Photovoltaics

ALD is a well-established industrial technique for manufacturing uniform thin films with nm-level precision, but is limited by the low growth rate. Spatial ALD (SALD) overcomes this limitation by separating the two precursors for fabricating metal oxides in space rather than in time, increasing the deposition rate by two orders of magnitude [1]. SALD manufacturing is the focus of our start-up company, NanoPrint Innovations Ltd (https://www.nanoprintinnovations.com).

The rapid nature of deposition by SALD is especially advantageous for growing oxides onto thermally-sensitive materials, such as metal-halide perovskites for photovoltaics. We show how reducing the deposition time from >30 min (for ALD) to <1 min (by SALD) opens up the range of deposition temperatures that can be used to grow SALD oxides (both n-type and p-type) on halide perovskite device stacks, leading to improvements in performance [2]. In particular, we focus on the use of SALD Cu₂O as a buffer layer in n-i-p-structured perovskite devices. The high mobilities and suitable band alignment of this buffer layer enables effective hole extraction, whilst simultaneously mechanically protecting the perovskite device from damage when sputter depositing the transparent top electrode. 16.7%-efficient semi-transparent perovskite devices are achieved, which, when stacked over silicon bottom cells, lead to 24.4%-efficient four-terminal tandem devices [3].

This talk finishes with perspectives on the potential and challenges of using spatial ALD to grow transparent conducting oxides with high figures-of-merit for photovoltaics [4].