Photovoltage enhancement: Analysis of polaron formation and charge transport at the junctions of organic polythiophene and inorganic semiconductors

We report the charge transport properties at the junction of organic polythiophene (PT) and inorganic semiconductors. Using a Kelvin probe and surface photovoltage spectroscopy, we have found that excitation of inorganic semiconductor band gaps led to hole migration across the inorganic-organic interface (IOI) and subsequently creation of polaron states in PT polymer chains. Of particular interesting is that these polaron states yield photovoltage responses initially at 675 run, and eventually over the entire region of the visible spectrum. Because of their long lifetime (hours to days), the density of these polaron states increases with the exposure time of photoexcitations of the inorganic semiconductor until saturation is reached. The net result is that photovoltage is enhanced over the visible spectrum through charge transfer of polaronlike states in PT to inorganic semiconductors. Sunlight can induce obvious photovoltage enhancement at these IOI junctions, which show potential promise in the future application of large area photovoltaic technology.