Mi‐Ri Choi

A highly efficient simplified organic light-emitting diode (OLED) with a molecularly controlled strategy to form near-perfect interfacial layer on top of the anode is demonstrated. A self-organized polymeric hole injection layer (HIL) is exploited increasing hole injection, electron blocking, and reducing exciton quenching near the electrode or conducting polymers; this HIL allows simplified OLED comprised a single small-molecule fluorescent layer to exhibits a high current efficiency (∼20 cd/A). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

We employed a low-cost solution-processed ultrathin insulating polymeric layer of poly(4-hydroxystyrene) (PHS), with a high glass transition temperature (Tg ∼ 185 °C), as an interfacial layer between the polymer:fullerene photoactive layer and the Al negative electrode for enhancing device power conversion efficiency (PCE) of polymer bulk-heterojunction photovoltaic cells and investigated the roles of the interfacial nanolayer by ultraviolet photoemission spectroscopy and capacitance–voltage measurement. The thin polymeric layer forms a dipole layer and causes the vacuum level of the adjacent negative electrode to shift upward, which resulted in an increase of the built-in potential. As a result, the open-circuit voltage and PCE of the device using a PHS nanolayer were remarkably improved. We finally achieved a very high PCE of 6.5% with the PHS/Al negative electrode which is even much better than that of the device using an Al electrode (5.0%). The solution-processed inexpensive PHS layer with a high Tg can be an attractive alternative to conventional vacuum-deposited low-work-function metal and insulating metal fluoride interfacial layers.