Study On Electrically Pumped Organic Semiconductor Lasers

Lasers based on organic semiconductor materials offer mechanical flexibility, low-cost production and spectrum tunability at the same time. Available organic lasers are pumped optically by additional laser sources such as inorganic solid state lasers or inorganic deep-blue laser diodes and light emitting diodes. Electrical pumping of an organic laser diode is expected to provide a further substantial reduction of the system costs, since an additional inorganic laser diode is not needed, which would open new applications for organic lasers in bioanalytics and spectroscopy.This dissertation discusses various loss processes which especially occur at high excitation and whose impact is in particular striking for organic laser diodes. Potential devices for an organic injection laser have to combine a low attenuation laser waveguide with the ability to support high current densities. We discuss some published concepts for organic laser diodes, which try to fulfill the above mentioned requirements.Although OLED's are highly efficient at low current densities, increases in nonradiative losses with excitation strength are a serious obstacle to obtaining an electrically pumped laser. The effect of all nonradiative processes is quantified by the external quantum efficiency-current density product,ηextJ. Some OLEDs which exhibit high efficiency at high current densities has been prepared in this work. Firstly, we developed a simple method, an ultrathin layer LiF sandwiched between exciton formation layer and electron transporting layer, to improve external quantum efficiencies (EQEs) of OLEDs. The value of EQE is far exceeds the theoretical upper limit of under a wide range of current density and shows nonlinear increase with current density. Secondly, since the coupled microcavity (CMC) structure can significantly suppress the transverse electric (TE) leaky modes, we studied the EL properties of CMC OLED. Thirdly, we studied the EL properties of the high efficient OLEDs with high work-function AZO anode, with p-i-n stuctures, with tendem structures, respectively.Torwards the realization of organic laser diode, we designed a microcavity organic laser, the design rules can be summarized as follow:In the emission layer, guest-host systems, with low self-absorption, should be used. Thus, the waveguide attenuation for the laser mode can be reduced. The injection of electrons and holes has to be balanced in order to achieve homogeneous exciton generation in the emission layer. By combine the electrode and the mirror, low optical absorption and highly reflective electrical contacts at organic-electrode interface was obtained.With a high quality factor (Q=237) microcavity formed by two high-reflective and low-loss contacts, we fabricated an electrically pumped organic laser device. A single longitudinal laseing cavity mode is obtained at 621.7 nm with a threshold current density of 860mA/cm2 under a room temperature pulse operation.