  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.
