Er@C₈₂ as a Bifunctional Additive to the Spiro‐OMeTAD Hole Transport Layer for Improving Performance and Stability of Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) based on 2,2′,7,7′‐tetrakis‐( N , N ‐di‐ p ‐methoxyphenylamino)‐9,9′‐spirobifluorene Spiro‐OMeTAD hole transport layer (HTL) have achieved a huge success in power conversion efficiency (PCE), but the required lithium bis(trifluoromethanesulfonyl)imide (Li‐TFSI) dopant in Spiro‐OMeTAD HTL is hygroscopic, not only impairing the charge transport but also inducing the instability of PSCs. Herein, Er@C 82 , which consists of a hydrophobic fullerene cage encapsulating an Er 3+ ion, is first introduced as a novel additive to modify the Li‐TFSI‐based Spiro‐OMeTAD HTL. By adding a tiny amount of Er@C 82 (0.09 mg mL −1 ) in the Spiro‐OMeTAD HTL, the PSC exhibits an efficiency promotion from 17.53% to 19.22%. The PCE enhancement is mainly attributed to the improved film quality of HTL after adding Er@C 82 , which promotes the oxidation of Spiro‐OMeTAD, resulting in faster hole transport and less charge recombination. Simultaneously, the hydrophobic Er@C 82 and the improved film quality of HTL lead to a dramatically enhanced stability of PSCs. Accordingly, the Er@C 82 ‐modified devices can maintain over 70% and 80% of the initial efficiencies after exposure in air for 400 h and in an Ar atmosphere for 2000 h, respectively. Therefore, this bifunctional Er@C 82 additive provides a promising pathway for fabricating highly efficient and stable PSCs.