Versatile Hole Selective Molecules Containing a Series of Heteroatoms as Self-Assembled Monolayers for Efficient p-i-n Perovskite and Organic Solar Cells

摘要

Inverted type perovskite solar cells (PSCs) have recently emerged as a majorfocus in academic and industrial photovoltaic research. Their multipleadvantages over conventional PSCs include easy processing, hysteresis-freebehavior, high stability, and compatibility for tandem applications. However,the maximum power conversion efficiency (PCE) of inverted PSCs still lagsbehind those of conventional PSCs because suitable charge-selective materialsfor inverted PSCs are limited. In this study, excellent hole-selective materialsfor inverted PSCs are introduced. A series of tricyclic aromatic rings containingO, S, or Se, respectively, as a core heteroatom, along with a phosphonic acidanchor, form a self-assembled monolayer (SAM) that directly contacts theperovskite absorber. The influence of heteroatoms in the aromatic structure onthe molecular energetics and operating characteristics of the correspondinginverted PSCs is investigated using complementary experimental techniquesas well as density functional theory (DFT) calculations. It is found that all ofthe SAMs formed an energetically well-aligned interface with the perovskiteabsorber. The interaction energy between the Se-containing SAM and perovskiteabsorber is the strongest among the series and it reduces the interfacialdefect density, in turn leading to an extended charge carrier lifetime. As a result,PSCs incorporating the Se-containing SAM achieves a PCE of 22.73 andretains ≈96 of their initial efficiency after a maximum power point trackingtest of 500 h without encapsulation under ambient conditions. All of the SAMsare then employed in organic solar cells (OSCs). Again, the Se-containing SAMbasedOSCs demonstrates the highest PCE of 17.9 among the threemolecular SAM-based OSCs. This study demonstrates the great potential forprecisely engineered SAMs for use in high-performance solar cells.