Dark currents in bulk heterojunction devices for imaging applications: The effect of a cathode interfacial layer

While sol-gel-processed metal oxides are widely used as an electron transport layer to enhance photovoltaic performances, their effect on photodetector application was not studied. We found sol-gel-processed titanium oxide deteriorated dark current characteristics in reverse biases by almost two orders of magnitude, whereas bare Al cathodes exhibited ideal dark current characteristics. Increased dark current came from space charge limited currents in microscopic p-i-p metal-semiconductor-metal configurations. The spatial variation of workfunction values was believed to form local leakage paths by partial filling of traps on the surface of sol-gel titanium oxide.