Despite decades of research in the emerging field of organic electronics, little is known about the behavior of holes, positively charged electron deficiencies that physicists treat as mobile entities. Electron and hole sta-tistics are crucial parameters of semiconductors, highlighting the importance of hole research in organic devices. Josh Bol-ingcr et al. have obtained newrninsight into the origin of holesrnin an organic polymer, MEH-PPV, finding that holes arise only when the polymer is excited by light that creates an exciton (a hole paired with an electron that has energy greater than the valence band). The exciton attracts holes into the polymer molecules in the presence of an electric field bias. The authors used an indirect single-molecule fluorescence imaging technique to visualize a layer of sparse MEH-PPV molecules underneath a layer of a strong organic hole donor material. They observed an exponential-like decay in fluorescence, which they attribute to the arrival of holes, but
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