Improving the Barrier Properties of Tin Oxide in Metal Halide Perovskite Solar Cells Using Ozone to Enhance Nucleation

We investigate tin oxide growth on fullerene (C60) by atomic layer deposition (ALD) for C60/oxide bilayer electron selective contacts in P-I-N metal halide perovskite (MHP) solar cells. An in situ ozone functionalization step is incorporated in an ALD SnOx process to suppress sub-surface growth, leading to improved internal barrier performance of ALD SnOx thin films grown on fullerene surfaces. We show that this approach decreases the water-vapor transmission rate of C60/ALD SnOx barriers by an order of magnitude and improves the barrier properties against gas, solvent, and halide migration. Furthermore, ozone-treated SnOx barriers can narrow photovoltaic performance distribution without compromising efficiency. We demonstrate the universality of this approach in wide-, intermediate-, and low-gap perovskite systems and further show that enhancement of the ALD barrier layer is critical toward improving the yield of all-perovskite tandem solar cells. Two-terminal all-perovskite tandem solar cells incorporating ozone nucleation are reported at over 24% photovoltaic conversion efficiency.