An electrically driven organic semiconductor laser

Abstract

This thesis presents the design and demonstration of an electrically driven organic semiconductor laser. The laser utilized an indirect pumping structure where the current injection section was spatially separated from the gain region.

To realize an electrically driven organic semiconductor laser, a low threshold polymer DFB laser and high brightness OLED were developed separately. Using BBEHP-PPV polymer and a high Q-factor substructured DFB cavity, the optimized optical laser threshold was 92 W/cm². The OLED was carefully designed to maximize the output power density and suppress heat accumulation. A p-i-n OLED on flexible parylene-nanolaminates (PNPN) substrate was designed and fabricated. Under pulsed operation, the OLED showed the highest reported output power density (46 W/cm² at 6.7 kA/cm²), a factor of 30 times improvement on the best deep blue pulsed OLEDs.

An effective way to integrate OLED and the polymer laser was developed where the two sections were held together in optical contact so that the laser could access the enhanced power density.
The integrated device showed a laser threshold current density of 2.83 kA/cm² with a narrow emission peak at 542.2 nm. The emission beam when operated above the threshold had a double lobe beam profile and a strong linear polarization parallel to the grating groove direction. The divergence of the laser was measured to be 2.4 mrad. The operational lifetime of the electrically driven device was 9.57×10⁴ pulses. Overall, the results presented in this thesis show strong evidence that an electrically driven laser was achieved.

An assisted pumping measurement was developed to estimate the irradiance transferred from the OLED to the gain medium. On a different integrated sample, the OLED could transfer about 100 W/cm² of electroluminescence to the polymer laser at 5.2 kA/cm². This is consistent with the simulation of outcoupling efficiency.

Date of Award	29 Nov 2023
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Ifor David William Samuel (Supervisor) & Graham Turnbull (Supervisor)