Self-assembled monolayers featuring multi-chlorinated carbazole unit for improving hole extraction efficiency in organic photoelectronic device

• A novel self-assembled monolayer named 4Cl-PACz was synthesized and applied in organic photoelectronic device. • upgrading the work function and modulating surface morphology of the ITO substrate by 4Cl-PACz. • A champion PCE of 18.2% was obtained in 4Cl-PACz based OSCs. • Enhanced luminance and efficiency values in OLED device based on 4Cl-PACz. Typical PEDOT: PSS hole-transporting layer always suffer from the unmatched energy level, harsher acidity and severe hydroscopicity, which further inducing the severe degradation of device performance and long-term stability simultaneously. Herein, we explore a novel carbazole derived molecule 4Cl-PACz as self-assembled monolayers anchoring directly onto the indium tin oxide (ITO) substrate. The 4Cl-PACz not only exhibits superior optical transmittance than PEDOT: PSS in visible and near-infrared region, but also could upgrade the work function, thus leading to more matched energy level alignment with donor materials to facilitate the hole extraction. Furthermore, 4Cl-PACz is proven to efficiently modify the surface morphology of ITO electrode while simultaneously optimizing the phase-separation of the active layer spin-coated atop. Consequently, devices based on ITO/4Cl-PACz system output a power conversion efficiency (PCE) of 16.8% based on PM6:Y6 system. The improved performance is mainly attributed to the improvement of energy level alignment and surface morphology, thus leading to improved charge extraction, lower trap-assisted recombination and longer carrier lifetime. Encouragingly, a higher PCE of 18.2% can be realized when PM6:L8-BO was employed as active layer. Moreover, the optimized OLED based on 4Cl-PACz also presents improved carrier transport, with enhanced luminance and efficiency values than PEDOT: PSS derived ones. This work manifests the advantage of the proposed 4Cl-PACz material for realizing high-performance and stable OSCs and OLEDs.