Methoxy-Functionalized Conjugated Self-Assembled Monolayers as a Hole-Selective Contact for Inverted Perovskite Solar Cells

In recent years, significant progress in inverted (p-i-n) perovskite solar cells (PSCs) has been observed, primarily due to the development of innovative self-assembled monolayer (SAM) materials for the hole transport layer (HTL). SAM materials have gained more popularity over the conventional polymer HTL material poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) because of their efficient hole transport and ability to passivate interfaces. Conjugated SAMs are considered as a good choice for PSCs because of their electrical and photostability. In this research, methoxy-functionalized conjugated SAMs (C21 and C22) were synthesized and studied for inverted Pb-based PSCs. Good coverage of the perovskite layer was observed on the C21 and C22 SAMs. The SAM molecules on fluorine-doped tin oxide (FTO) tuned the work function (WF) of the FTO with the number of methoxy groups in the SAM molecule. The methoxy group positioned at ortho- and para-positions was found favorable for the growth of good perovskite layers on the SAM surface. As a result, the C22 SAM with the Pb-based triple cation perovskite in the inverted PSC exhibited a champion power conversion efficiency (PCE) of 21.58%. These findings suggest that conjugated SAM functionalized with methoxy groups at the ortho- and para-positions are promising for the further development of inverted PSCs.