“…The OPDs having conventional structures that absorb light from the bottom are not desirable for stacking the device on an integrated circuit, because bottom thin-film transistors (TFTs) reduce the aperture ratio and hinder OPD light absorption. − Instead, an OPDs with transparent top electrode, i.e., a top-absorbing OPD, is necessary. Despite the research on a bottom hole-collection integrated on Si readout circuitry, a bottom electron-collecting electrode is preferred because oxide TFTs having a high carrier mobility, a low processing cost and temperature, and film uniformity are basically n-type. Thus, to apply an OPD to an integrated circuit, the OPD needs to have the following inverted structure: a bottom cathode, an electron extraction layer, a photoactive layer, a hole extraction layer, and a transparent top anode.…”