Electroluminescent characteristics of one-dimensional silicon chains in dialkyl polysilanes

We investigate the electroluminescent characteristics of polysilane-based single-layer light-emitting diodes (LEDs) which employ poly(di-n-hexylsilane) (PDHS) or poly(di-n-butylsilane) (PDBS) (PDHS-LED and PDBS-LED, respectively). The PDHS-LED exhibits an electroluminescence (EL) identical to its photoluminescence (PL), which is composed of an emission only in the near-ultraviolet (NUV) region. By contrast, the PDBS-LED exhibits EL in both the visible and NUV regions. Although these two polysilanes differ only in terms of their substituent groups, their device characteristics vary considerably; the PDBS-LED exhibits a larger device current, inferior rectifying behavior, and a lower turn-on voltage than the PDHS-LED. This observation is inconsistent with predictions based on the hypothetical band diagrams of these two LEDs. We have demonstrated the fundamental EL characteristics of σ-conjugated one-dimensional Si chains by using PDHS, which has a highly ordered backbone conformation and negligible structural defects.