High-efficiency inverted bulk heterojunction polymer solar cells with UV ozone-treated ultrathin aluminum interlayer

Highly efficient inverted heterojunction polymer solar cells were developed with an UV ozone-treated ultrathin aluminum interlayer between the active layer and indium tin oxide (ITO). The ultrathin aluminum interlayer was fabricated by thermally depositing on ITO and subsequently treating it with UV ozone. Thus, it forms an alumina layer that improves electron extraction. Power conversion efficiency of 3.92%, open circuit voltage of 0.583 V, short-circuit current of 10.95 mA/cm(2) and fill factor of 0.614 were achieved on the inverted devices of a poly(3-hexylthiophene) and [6,6]-phenyl-C-61-butyric acid methyl ester blend under AM1.5 illumination (100 mW/cm(2)), which are significantly higher than that of the control device without the interlayer. The significant improvement in device performances is attributed to the reduction in energy barrier for electron extraction due to the formation of alumina, as revealed by ultraviolet photoelectron spectroscopy. (C) 2010 American Institute of Physics. [doi:10.1063/1.3479916]