Deuterium Renders Fast Risc and Low Non‐Radiation Decays of TADF Emitters

Abstract A simple strategy to simultaneously achieve fast reverse intersystem crossing (RISC) and low non‐radiative decay rates in thermally activated delayed fluorescence (TADF) emitters is still lacking. Here, the green TADF emitters containing aromatic ketones and prepared D‐Ph and D‐PhCz containing different amounts of deuterium are deuterated to study the mechanism of deuterium on the performance improvement of TADF devices. Due to the heavy atom effect of deuterium, the non‐radiative transition rate constant ( k nr ) of D‐Ph and D‐PhCz decreases. Most importantly, deuterium reduces the reorganization energy ( λ ) of (T 1 ‐S 1 ), which greatly improves the reverse intersystem crossing rate constant ( k RISC ) and the exciton utilization efficiency. The results show that the external quantum efficiency of D‐Ph and D‐PhCz increases to 25.69% and 24.92%, respectively. This study provides a simple and efficient strategy for reducing non‐radiative energy loss and increasing k RISC to achieve high‐performance TADF emitters.