Ultrathin oxygen deficient SnOx films as electron extraction layers for perovskite solar modules

The design of high-quality junctions capable of efficiently extracting carriers from perovskite-based absorbers is key in the transition from lab-scale devices to modules. In the so-called n-i-p configuration, SnO2 nanoparticle (np-SnO2) films have been thoroughly investigated as electron transporting layers (ETLs) in view of their good optimal band alignment, chemical stability and appropriate surface chemistry for nucleating high-quality perovskite films. In this report, we show for the first time that np-SnO2 films are characterized by a heterogeneous surface electronic landscape and introducing quasi-monoenergetic conformal layers between the transparent conducting oxide (TCO) and the np-SnO2 film can lead to significant improvement in perovskite solar modules. These SnOx extraction layers are developed using a highly innovative plasma-modified atomic layer deposition (PMALD) tool, which enables tuning the Sn : O ratio, conductivity, and effective work function. Energy-filtered photoemission electron microscopy (EF-PEEM) shows a remarkably homogeneous surface electronic landscape of PMALD SnOx. We examine the impact of PMALD-SnOx in an n-i-p device configuration, with poly(triarylamine) (PTAA) as the hole transporting layer, which leads to the improvement in perovskite module power conversion efficiency from 17.9% to 20.1%, with an active area of 23.2 cm2. Furthermore, the devices retained 92% of their initial efficiency for 2700 h at 85 degrees C and 85% relative humidity and 96% for 1000 h under continuous illumination with maximum power point tracking.