Magnetron sputtered ZnO electron transporting layers for high performance perovskite solar cells

An ideal electron transporting layer (ETL) of perovskite solar cells (PSCs) requires reasonable energy levels, high electrical conductivity and excellent charge extraction. The low processing temperature makes ZnO a promising ETL for PSCs; however the widely used solution-processed ZnO films often suffer from high-density surface defect states, which might cause severe charge recombinations at the ETL/perovskite interface and accelerate the chemical decomposition of perovskite materials. In this work, we employed the vacuum-based magnetron sputtering method to deposit ZnO ETLs, which significantly reduces the number of oxygen vacancies and hydroxyl groups on the ZnO surface. The magnetron sputtered ZnO based CH3NH3PbI3 PSCs yield a considerable power conversion efficiency (PCE) of 13.04% with excellent long-term device stability. Furthermore, aiming to improve the ETL/perovskite interface for more efficient electron extraction, a bilayer ZnO/SnO2 ETL was designed for constructing high-efficiency PSCs. The detailed morphology characterization confirms that the bilayer ZnO/SnO2 provides a low-roughness film surface for the deposition of high-quality perovskite films with full coverage and long-range continuity. The carrier dynamic study reveals that the presence of the SnO2 layer results in the formation of favorable cascade energy alignments and facilitates the electron extraction at the ETL/perovskite interface. As a result, compared with the ZnO-based PSCs, the device constructed with the bilayer ZnO/SnO2 ETL delivers an improved PCE of 15.82%, coupled with a reduced hysteresis.