Simultaneous excess PbI2 management and promoted band alignment by interface modulation for highly efficient perovskite solar cells

Excessive PbI 2 and energy level mismatch can cause severe hysteresis effects and instability in perovskite solar cells. N-(Trifluoroacetyl) glycine (TFAG) was employed in this work as a multifunctional additive to modify the interface between the perovskite layers and the SnO 2 electron transport layer (ETL). The SnO 2 surface's oxygen vacancy defects might be passivated by the carboxyl groups in TFAG efficiently coordinating with Sn 4 + . Ultraviolet photoelectron spectroscopy (UPS) indicated that energy band of SnO 2 shifted to higher level, which was beneficial for promoting band alignment of ETL and perovskite layer. Larger grains and less excess PbI 2 were observed in the modified perovskite films. The Urbach energy dropped, suggesting more ordered grain boundaries and the decrease of the density of defect states. As a result, the hysteresis index decreased from 13.16% to 4.43% and the power conversion efficiency (PCE) of PSCs increased from 20.13% to 22.36% after modification. Furthermore, PSCs with TFAG exhibit superior long-term stability, retaining 88% of their initial PCE after 2250 h of room temperature storage in a nitrogen-filled glove box, as well as 79% of their initial efficiency after 10 days in a dark air environment at room temperature and 50% humidity. This work utilizes amino acid derivatives to effectively reduce excess PbI 2 , improve interfacial contact and promote energy level matching, thereby enabling highly efficient and stable PSCs.