The viability of solar power is currently limited by the expense and processing limitations of existing inorganic technology. Organic semiconductors offer the possibility of scalable, economically appealing solar cell technologies. Quinacridone is a promising material which has recently been shown to have electronic properties comparable to the fully π-conjugated, but structurally similar pentacene, while remaining chemically stable in air. In order to better understand the potential of quinacridone as a candidate material for viable, next generation solar cells we have fabricated a number of thin-film samples and device structures and characterized them by a suite of optical and electronic tests.
Absorbance and temperature-dependent photoluminescence studies were used as a probe to investigate the electronic states of vapor deposited quinacridone thin films, finding exciton binding energies consistent with excitonic states delocalized across several molecules. Impedance spectroscopy measurements were used to measure the temperature-dependent photoconductivity of Gold : Quinacridone : Gold MSM structures, finding that quinacridone is almost an order of magnitude more conductive under laser illumination. Diode structures of ITO:PEDOT:Quinacridone:Al were fabricated to measure the IV characteristics under light and dark conditions, as well as the transient photocurrent and photovoltage. These studies confirmed that the light current generation of the diodes was not limited by charge transfer state lifetimes, as charge extraction occurs on a much faster time scale. However, we found that the low mobility of our quinacridone thin films, caused by their low crystalline order, decreased the probability of exciton dissociation, limiting the production of usable power
