Organic Photovoltaic Devices

Organic light emitting devices, including molecular light emitting devices (MLEDs) and polymer light emitting devices (PLEDs) are commonly consist of one or several organic layer(s) sandwiched between an anode and a cathode.When electrons and holes are injected respectively from cathode and anode into the organic layer by a bias voltage, the two types of carriers migrate towards each other and a fraction of them recombines to form light emission.The focus of this study devoted to the interfical modifications of organic molecular light emitting devices. The electrode modifications include using a low work function cathode, a high work function anode material or inserting a very thin electrode modifier between organicr layer and electrode for enhancing the injection efficiency of electrons and holes, which leads to higher perfomances of the devices.A very thin(about 1nm) buffer layer of LiF inserted between electron transport layer (ETL) and Al cathode was applied to improve the injection efficiency of electrons,which leads to an improvement of luminous intensity of 30.5mcd and a higher luminous brightness of 1.22kcd/m~2 at 8.2V, the largest luminous efficiency of 0.93lm/W at 5.5V drive voltage.On anode modification, a thin ZnPc or C60 layer was inserted between the hole transport layer (HTL) and the indium-tin-oxide (ITO) substrate for improving the luminous brightness, luminous efficiency and threshold voltage.The molecular emitting devices using the ZnPc buffer layer show better performances than that of the unmodified devices. The devices using ZnPc buffer layer have shown the largest luminance brightness of 1.428kcd/m~2 at a drive voltage of 7.42V and the best luminous efficiency of 1.41lm/W at 4.3V compared to the corresponding values of 1.212 kcd/m~2 at 8V and 0.93lm/W at 5.5V in unmodified devices. Furthermore, we found the morphology of the devices with buffer layer becomes smoother than those without buffer layer. We have demonstrated the modified devices with C60 showed the best luminous brightness of 1.756kcd/m2 at 8.2V and the largest luminous efficiency1.25lm/W at 5V. At the same times, the modified anode with ZnPc or C60 could effectively decrease the thresholed voltage on organic light emitting devices.Besides of these, the morphorloy and conductivity of Poly (ethylenedioxythiophene) /Poly (4-styren esulphonate) (shortened form PEDOT:PSS) films were studied by using atomic force microscope (AFM) and a measuring equipment of resistivity.The function of PEDOT:PSS layer is to improve the work function and the smoother morphology of ITO,whiceh effectively leads to enhance the injection efficiency of holes and the performances of devices.