Silicon-based Infrared And Visible Organic Electroluminescence

This dissertation systemically studies one possible silicon light source: Silicon-based organic electroluminescence (EL) devices. The main attentions are focused on the following aspects:1. By doping an erbium complex, erbium (III) 2, 4-pentanedionate [Er(acac)3] ,into the AlQ layer, we fabricate a series of infrared emission organic light emitting diodes (OLEDs) with structures of p-Si/ SiO2/ NPB/ AlQ/ AlQ:Er(acac)3/ AlQ/ Sm/ Au. The 1.54μm EL from Er3+ is observed. The impact of doping level of Er(acac)3 in AlQ on 1.54μm EL intensity is studied. A competitive EL mechanism from the AlQ and Er(acac)3 is found and discussed.2. In the infrared silicon-based organic light emitting diode, the quality of pure Er(acac)3 film is too poor, so we try another material, ErQ [Erbium(III) tris(8-hydroxyquinoline)]. We introduce a sandwich organic structure NPB/ ErQ/ AlQ, and the EL intensity is greatly improved. We design a nanometer thick polycrystalline silicon (NTPS) anode which is fabricated with the magnetron sputtering technology followed by the nickel-induced crystallization process. The 1.54μm EL efficiency of the infrared OLED with NTPS anode is two orders of magnitude higher than that of the OLED with a structure of thick crystalline silicon/ NPB/ ErQ/ Al, which is similar to the silicon-based infrared OLED reported in literature.3. Top-emission organic light-emitting devices with a configuration of n-Si (cathode) / Au:Sb / Sm / AlQ / NPB / V2O5 / Au (anode) are studied. We dope Sb at the n-Si surface to increase the electron concentration and then deposite Sm to reduce the work function of the cathode. We have found high surface electron concentration and surface modification of n-Si are beneficial to the electron injection. Power efficiency of device with 10-3 ?cm n-Si/Au:Sb cathode is 10 times more than that of the device with 10 ?cm n-Si/Au cathode. With optimized thickness of V2O5, such device exhibits much higher EL efficiency (0.8 lm/W) than the conventional top-emission organic light-emitting devices with p-Si or n-Si anodes reported previously (0.2 lm/W).4. We study a series of ultrathin-SiO2-layer-passivated p-Si anode organic light emitting diodes (Si-OLED) by changing the resistivity of p-Si anode and changing the electron injection and transport layer. We have found that hole injection can be enhanced simply by selecting a lower-resistivity p-Si anode to match an electron injection enhancement for Si-OLED. For a Si-OLED with ordinary AlQ electron transport layer , the optimized resistivity of the passivated p-Si anode is 40 ?cm; For that with n-doped Bphen electron transport layer, it decreases to 5 ?cm. Correspondingly, the maximum luminance efficiency increases from 0.3 to 1.9 lm/W, even higher than that of an ITO control device (1.4 lm/W). Predictably, if a more efficient electron injection and transport material is used, the optimum resistivity of the passivated p-Si anode will decrease and the luminance efficiency will increase. This opens a route to fabricate efficient Si-OLEDs using passivated p-Si anode, even much better than ITO-based ones.5. We have succeeded in achieving a silicon light source with a power conversion efficiency of more than 10%. The device structure is p-Si (5 ?cm)/ SiO2(~2nm)/ NPB / CBP: (ppy)2Ir(acac) / Bphen /Bphen: Cs2CO3 / Sm / Au. In this diode, an ultrathin SiO2-layer-passivated p-silicon anode offers a strong hole injection; an electrical doping electron transport material offers a strong electron injection; The phosphor (ppy)2Ir(acac) is used as a highly efficient emitter; a low work function and highly transparent metal bilayer Sm/Au is used as a cathode. The device turn-on voltage is 3.2 V. The maximum luminance efficiency and maximum luminous power efficiency reach 69 cd/A and 62 lm/W, respectively, corresponding to an external quantum efficiency of 17%.