The authors are engaged in developing a novel image acquisition system called Elgraphy, which is a combination of electrophotography and liquid crystal technology. One desirable property that the photosensor used for Elgraphy (Elgraphic photosensor) should have is sensitivity over a wide range of the visible spectrum in order to accurately capture color images. The authors found that, in the Elgraphic photosensor, which exhibits photocurrent amplification, the addition of a special charge transport material (CTM) to the charge transport layer (CTL) has the effect of enhancing the sensitivity in the blue light region. This effect is attributable to the following mechanism: Blue light that has passed through the charge generation layer (CGL) is absorbed by the CTM, where it excites the CTM to fluoresce in the absorption band of the CGL. The CGL absorbs the fluorescence, which induces the generation of photocarriers inside the CGL, thus giving rise to photocurrent amplification similar to the photoconduction mechanism that occurs in the green and red light regions.
D. Aoki, S. Hikosaka, E. Inoue, "Organic Photosensor in Elgraphy—Part III Enhancement of Spectral Sensitivity by Addition of Fluorescent Charge Transport Material" in Journal of Imaging Science and Technology, 2002, pp 338 - 343, https://doi.org/10.2352/J.ImagingSci.Technol.2002.46.4.art00011