Single emission spectrum measurement enables control of organic LED emission zone giving ultralong device lifetime

Abstract Device optimization of light-emitting diodes targets the most efficient conversion of electrically injected charges into emitted light. Where charges recombine and where light is emitted from is known as the emission zone. Determining its form is key to better understanding the physical processes determining device performance. However, a thorough measurement study has not been shown. Here we present an accessible technique to visualize the emission zone in unprecedented detail at all luminescing current densities. Only a single emission spectrum must be measured (at normal direction to the device layers with no additional optics) and compared with the simulated emission spectrum. This method allows physical understanding based, instead of speculative, optimisation of LED device architectures. We demonstrate its impact by examining the device structure – emission zone – lifetime relationships of a thermally activated delayed fluorescence OLED to achieve an ultralong 4500 hour T95 lifetime at 1000 cd/m2 with 20% external quantum efficiency.