Elimination of charge accumulation by a self-assembled cocrystal interlayer for efficient and stable perovskite solar cells

Abstract

Elimination of interfacial charge accumulation and inhibition of ion migration are still challenging for promoting both efficiency and operational stability of perovskite solar cells (PVSCs) with 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spiro bifluorene (spiro-OMeTAD). Here an innovative interface engineering, self-assembled cocrystal layer (SAM-CL) for PVSCs is constructed from a 1-pyrenemethylamine hydrochloride (PRMA) monolayer on the perovskite surface and 2,3,5,6-tetrafluoro-7,7′,8,8′-tetracyanoquinodimethane (F4TCNQ) doped in spiro-OMeTAD through intermolecular π–π interactions and hydrogen bonds. SAM-CL optimizes interfacial energy level alignment by a strong charge-transfer effect, thereby eliminating interfacial charge accumulation. Moreover, the excellent barrier effect of large pyrene rings and fluorine atoms in SAM-CL effectively hinders ion migration and moisture invasion, thus significantly improving the stability of PVSCs. The resulting PVSCs yield a power conversion efficiency (PCE) of 24.03% with a high open circuit voltage of 1.21 V and deliver impressive stability, which can maintain 85% of initial PCE after over 1800 h in air with a relative humidity of 70–80% without encapsulation.