Enhanced performance of an inverted‐type polymer solar cell is reported by controlling the surface energy of a zinc oxide (ZnO) buffer layer, on which a photoactive layer composed of a polymer:fullerene‐derivative bulk heterojunction is formed. With the approach based on a mixed self‐assembled monolayer, the surface energy of the ZnO buffer layer can be controlled between 40 mN m−1 and 70 mN m−1 with negligible changes in its work function. For the given range of surface energy the power conversion efficiency increases from 3.27% to 3.70% through enhanced photocurrents. The optimized morphology obtained by surface energy control results in the enhanced photocurrent and transmission electron microscopy analysis verifies the correlation between the surface energy and the phase morphology of the bulk heterojunction. These results demonstrate that surface energy control is an effective method for further improving the performance of polymer solar cells, with potentially important implications for other organic devices containing an interface between a blended organic active layer and a buffer or an electrode layer.

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The eukaryotic initiation factor 5A (eIF5A), a factor essential for eukaryotic cell proliferation, is the only cellular protein containing the polyamine-derived amino acid hypusine [N -(4-amino-2-hydroxybutyl)lysine]. Hypusine is formed in a posttranslational modification that involves two sequential enzymatic steps catalyzed by deoxyhypusine synthase and deoxyhypusine hydroxylase (DOHH). By screening a Saccharomyces cerevisiae GST-ORF library for expression of DOHH activity, we have cloned YJR070C as the gene encoding DOHH and identified the human homolog DOHH gene, HLRC1. Purified recombinant yeast and human DOHH enzymes effectively catalyzed hydroxylation of the deoxyhypusine residue in the eIF5A intermediate. Overexpression of human DOHH along with eIF5A precursor and deoxyhypusine synthase was required for overproduction of mature, hypusine-containing eIF5A in 293T and other mammalian cells. The Saccharomyces cerevisiae strain with deletion of YJR070C contained only deoxyhypusine but no hypusine, indicating that YJR070C was the single DOHH gene in this organism. One highly conserved DOHH homolog gene is found in a variety of eukaryotes from yeast to human. Sequence and structural analyses reveal that DOHH belongs to a family of HEAT-repeat-containing proteins, consisting of eight tandem repeats of an ␣-helical pair (HEAT motif) organized in a symmetrical dyad. The predicted structure is unrelated to the double-stranded ␤-helix type structures of the Fe(II)-and 2-oxoacid-dependent dioxygenases, such as collagen prolyl or lysyl hydroxylases. However, metal coordination sites composed of four strictly conserved histidine-glutamate sequences were identified, suggesting that DOHH enzymes have convergently evolved an iron-dependent hydroxylation mechanism. eukaryotic initiation factor 5A ͉ hypusine ͉ YJR070C