Li-TFSI Endohedral Metal-Organic Frameworks in Stable Perovskite Solar Cells for Anti-Deliquescent and Restricting Ion Migration

Abstract Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) is generally regarded as a conventional p-dopant for classical hole transport material Spiro-OMeTAD, which improves the hole mobility and conductivity of hole-transporting layer (HTL). However, the hygroscopic Li-TFSI would absorb moisture and accelerate the degradation of perovskite film, causing a decline in the long-term stability of perovskite solar cells (PSCs). Herein, a novel dopant Li-TFSI endohedral metal-organic frameworks (namely Li-TFSI@NH2-MIL-101) is constructed for reducing the amount of Li salt and resisting the attack from water molecules. With a significantly decreased Li salt loading mass, the optimal power conversion efficiency (PCE) of 19.01% is achieved for Li-TFSI@ NH2-MIL-101 doped PSCs, which is comparable to that of conventional devices (19.23%). Furthermore, the strong interaction between ammonium groups (-NH2) and uncoordinated Pb2+ ions would passivate the trap states and inhibit ion migration at perovskite/hole transport layer interface, which further improve the device stability. Importantly, this approach realizes an enhanced stability for approximately 10-fold that of conventional devices at the preliminary stage (time to reduce to 90% of initial PCE). The Li-TFSI@NH2-MIL-101 doped PSCs display impressive property stability retaining over 85% of the optimal PCE after 3600 h storage in ambient environment (room temperature and RH ≈ 40%).