Role of the Blend Ratio in Polymer:Fullerene Phototransistors

Because of their ability to combine detection and processing into a single element, phototransistors have the potential to be a disruptive optical-detection technology. Unfortunately, however, at present the relationship between current and incident optical power density is complicated and poorly understood. In this report, we investigate how the ratio of polymer to fullerene affects the performance of organic phototransistors. We find the surprising result that even a small percentage (1% by weight) of polymer can modify the optical response of organic phototransistors to green light significantly. Polymer:fullerene phototransistors such as those demonstrated in this report have the combined advantages of being highly optically transparent to the excitation wavelength and being unipolar.