Built-in fields in nanodimensional organic ferroelectric-semiconductor heterostructures: The principal role of molecular probes

The external and internal (built-in) macroscopic fields in a nanodimensional heterostructure consisting of organic ferroelectric and organic semiconductor layers between transparent (indium tin oxide) and semitransparent (aluminum) electrodes have been studied. The fields were measured using optical probe molecules in both the semiconductor layer (copper phthalocyanine, CuPc, with intrinsic specific features of the absorption spectrum) and the ferroelectric layer (poly(vinylidene fluoride)-trifluoroethylene copolymer) in which a molecular probe was introduced as a dopant (palladium tetraphenylporphyrin) possessing a characteristic spectrum. Local fields were measured using electroabsorption, followed by a recalculation in the macroscopic fields. It is established that the amplitude and direction of a macroscopic built-in field in the semiconductor can be controlled by changing the polarization of the heterostructure using pulses of external voltage applied to the heterostructure. This effect can be useful for increasing the efficiency of organic converters of solar radiation energy into electricity.