Enhanced performance of pulse driven small area polyfluorene light emitting diodes

We have investigated the performance of conjugated polymer light emitting diodes (LEDs) as their active areas are reduced to dimensions typical for pixellated displays. We find that by reducing the active diameter of the device from our standard size $\text{(1.5×3\hspace{0.05em}}\mathrm{mm})$ to 50 μm, the current density that can be sustained before LED failure increases by a factor of 9. This increase in current density is mirrored by similar increases in maximum LED brightness. We propose that such effects occur due to improved thermal management in small area devices. Using pulsed driving schemes, devices with a diameter of 50 μm sustained current densities of $\text{5.1\hspace{0.05em}}{\mathrm{MA m}}^{\mathrm{-2}},$ and have emitted electroluminescence with a brightness of $\text{6.5\hspace{0.05em}}{\mathrm{Mcd m}}^{\mathrm{-2}}.$