Interface Electrode Morphology Effect on Carrier Concentration and Trap Defect Density in an Organic Photovoltaic Device.

Formation of Schottky barrier contact (SBC) leads reconstruction of charges at the metal/semiconductor (MS) interface because of the wave function overlap between semiconductor and metal contact. Not only is the Schottky barrier contact formation a signature of the material's work function, but also it is sensitive to the interface trap states, the crystal orientation of the interacting materials, and other interface properties. In this work, the effect of aluminum cathode morphology on the polymer Schottky diode and bulk heterojunction (BHJ) photovoltaic device performance is studied. The electron collecting contacts in Schottky diode and BHJ device have been deposited using aluminum in pellet and nanoparticle forms. Devices fabricated by using Al nanoparticle showed improvement in dark as well as photocurrent density. Significant enhancement in J leads to overall improved power conversion efficiency. Enhanced performance in Schottky structured diode and OPV device have been correlated with electrode microstructure and its interface properties such as improved electrically active contact and enhanced charge transport. Electrical conductivity is discussed based on enhanced electrical coherence across organic semiconductor and electrode interface. Therefore, the contribution of electrical enhancement leads to improvement in short-circuit current density (J) in BHJ solar cell which is due to reduced trap density. Further, PCE was correlated with the density of interface trap states studied by drive level capacitance profiling technique.