Enhancing Light Emission in Interface Engineered Spin-OLEDs Through Spin-Polarized Injection at High Voltages
The quest for a spin-polarized organic light emitting diode (spin-OLED) is a common goal in the emerging fields of molecular electronics and spintronics. In this device two ferromagnetic electrodes are used to enhance the electroluminescence intensity of the OLED through a magnetic control of the spin polarization of the injected carriers. The major difficulty is that the driving voltage of an OLED device exceeds of a few volts, while spin injection in organic materials is only efficient at low voltages. We report here the fabrication of a spin-OLED that uses a conjugated polymer as bipolar spin collector layer and ferromagnetic electrodes. Through a careful engineering of the organic/inorganic interfaces we have succeeded in obtaining a light-emitting device showing spin-valve effects at high voltages (up to 14 V). This has allowed us to detect a magneto-electroluminescence enhancement on the order of a 2.4 % at 9 V for the antiparallel configuration of the magnetic electrodes. This observation provides evidence for the long-standing fundamental issue of injecting spins from magnetic electrodes into the frontier levels of a molecular semiconductor. Our finding opens the way for the design of multifunctional devices coupling the light and the spin degrees of freedom.