Electric double layers allow for opaque electrodes in high performance organic optoelectronic devices

We report that opaque electrodes can be used for high-performance organic optoelectronic devices, facilitated by the electric double layers (EDLs) formed in ionic liquids. For the photocell, gold/poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl C-61 butyric acid methyl ester (PCBM)/ionic liquid/silver, the EDLs enable a large photocurrent response, without the electrodes being superimposed. The external quantum efficiency and responsivity can reach 61.2% and 272 mA/W, respectively. The specific detectivity can reach 1.9 x 10(13) Jones, which is larger than silicon-based detectors. This type of architecture will renew the operation principle and material choice for organic photocells, because transparency is no longer an indispensable condition for the electrodes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4762823]