Developing a gradient titanium dioxide/amorphous tantalum nitride electron transporting layer for efficient and stable perovskite solar cells

Metal oxides are extensively applied as one of the most potential electron transport layers (ETLs) in perovskite solar cells (PSCs). However, their inherent surface oxygen vacancies and imperfect energy level alignment with the perovskite layer usually result in photogenerated charge recombination at the ETL/perovskite heterointerface. Managing the interface defects and band alignment is significant to decrease energy loss and improve the power conversion efficiency of PSCs. Herein, we develop a gradient TiO2/a-TaNx (TOAN) ETL, which not only eliminates interfacial defects and improves the crystallization of perovskite films, but also displays good energy level alignment and charge transport characteristics. The MAPbI3 solar cells based on TOAN ETLs achieve an efficiency of 21.41% with an open-circuit voltage of 1.20 V and a short-circuit current density of 22.87 mA cm-2. In addition, the device with a TOAN ETL maintains 95% initial efficiency after 30 days in N2 without encapsulation and retains 91% of its initial efficiency after storing for 30 days in an atmospheric environment. This result demonstrates the effectiveness of an inorganic metal nitride as an interface modification layer and provides a reference for the further development of metal nitride electron transport layers. A gradient TiO2/a-TaNx electron transport layer was developed for perovskite solar cells. Insights into the relation between the surface elements, charge transfer dynamics, and crystallization of the perovskite have been elucidated in detail.