Device Geometry for Large Thickness Organic Solar Cells

Bulk heterojunction organic solar cells suffer a steep drop-off in power output as the thickness of the active layer increases due to the increased series resistance caused by the additional material. This is especially significant because large-scale manufacturing techniques require active layers of ∼300 nm, which is considered a thick active layer. We use computer simulations to investigate the effects of placing both the electron and hole carrying electrodes on the same side of the device with a thin insulating barrier separating them. The simulations divide the sample into small p- and n-type material regions, which are then modeled by a large resistor-diode network. This device geometry produces a relatively constant power output for all devices thicker than 75 nm. This is because there is almost no current flowing in the upper portion of the device, so changes in thickness have almost no effect on maximum power output. Placing both electrodes on the same side also produces a higher power output at all thicknesses than devices with electrodes on both sides. While this device geometry may be difficult to fabricate, it does increase the power output of thicker devices and allows for the creation of thickness independent devices.