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We report on the fabrication of highly efficient, semitransparent bulk heterojunction solar cells comprising poly[[9-(1-octylnonyl)-9h-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) blended with [6,6]-phenyl-C71-butyric acid methyl (PC71BM) esters as active layer. As semitransparent cathode sputtered aluminum doped ZnO was used in combination with a sputter damage preventing, thin (8 nm) TiOx layer processed from solution and a sputtered aluminum interlayer (ALI). The short circuit current improves for thicker ALIs due to increased reflectance at the cathode leading to average efficiencies of 4.0% for semitransparent solar cells. Comparable results (3.9%) were achieved for devices comprising thick absorbers and thin ALIs. [ABSTRACT FROM AUTHOR]

The sputter deposition technique is usually avoided for organic solar cells, despite its technological advantages, because it may potentially damage the organic absorber layer. The consequences of sputtering on device performance-presumably related to changes in the absorber morphology and defect distribution near the interface-are discussed. Despite its negative influence on as-deposited samples, sputtering in combination with thermal annealing can actually be beneficial for pure aluminum contacts, leading to efficiencies even better than those of cells with thermally evaporated cathodes, mainly due to an enhanced open-circuit voltage. [ABSTRACT FROM AUTHOR]