Limited Injection at Electrode/Organic Interface Induced Non-Ideal Diode Behavior in Planar Heterojunction Organic Photovoltaic Devices.

In this report, the non-ideal current density-voltage (J-V) characteristics of organic photovoltaic devices are studied in terms of the limited injection at both the anode and the cathode. The device comprises of indium-tin oxide (ITO), copper phthalocyanine (CuPc), fullerene, bathocuproine (BCP), and AI fabricated by a thermal evaporation system. For the anode, the work function of ITO is modified from 4.7 to 5.1 eV, which reduces the injection barrier of holes to CuPc (with ionization energy 5.1 eV) from 0.4 to 0 eV. Diminished s-shape curves are obtained through the reduced-barrier devices. To gain insight into the limited injection, a numerical method based on the continuity equation and the drift-diffusion model is employed to simulate the electrical properties of the devices. A non-ideal diode behavior of the J-V curve is also observed as a result of increasing the thickness of the BCP layer which prevents the injection of the electrons into the device. [ABSTRACT FROM AUTHOR]