Tailoring Crystalline Self-Assembled Monolayers via Skeletal Isomerization for Exceptional Efficiency and Reproducibility in Organic Solar Cells

Abstract

The carbazolyl phosphonic acid-based self-assembled molecules (SAMs) are a promising candidate as hole transport layers (HTLs) for organic solar cells (OSCs). However, the SAM films tend to have incomplete surface coverage on the electrode, such that interfacial defects adversely affecting device performance and reproducibility. To address this issue, we design three asymmetric SAMs (4PACz-1N, 4PACz-2N, and 4PACz-3N) featuring isomerized naphthyl-carbazole skeletons. Skeleton isomerization simultaneously regulates dipole properties to elevate the work function of ITO anodes and minimizes energy barriers for hole extraction. Meanwhile, the conjugation skeleton expansion can further promote molecular stacking and reduce surface energy, leading to more complete coverage on the ITO and more intimate contact with the active layer, thereby enhancing the reproducibility of the device. Consequently, these isomerized SAMs demonstrate synergistic improvements in charge extraction efficiency, device reproducibility, and interfacial stability. These features significantly improve charge dynamics and interfacial stability, and demonstrate universal applicability in numerous systems. Notably, binary devices based on 4PACz-1N can achieve an excellent efficiency of 20.27% with outstanding device stability. This work highlights the significance of the skeleton isomerization strategy for developing highly efficient HTL.