Sensitive Photodetection with Photomultiplication Effect in an Interfacial Eu^2+/3+ Complex on a Mesoporous TiO₂ Film

A simple device structure composed of an interfacial Eu 2+/3+ complex on a mesoporous TiO 2 film is developed by a solution process and acts as the high-performance photodetector with photomultiplication phenomena. The electron transfer from the photoexcited organic ligand, 2,2′:6′,2″-terpyridine (terpy), as a photosensitizer to TiO 2 is accelerated by the reduction level of Eu 3+/2+ ions chemically bonding among terpy and TiO 2, resulting in the generation of a large photocurrent. It is worth noting that its external quantum efficiency is in excess of 10 5 % under applied reverse bias. The corresponding responsivity of the device is also determined to be 464 A/W at an irradiation light intensity of 0.7 mW/cm 2 (365 nm), which is more than 3 orders of magnitude larger than those of inorganic photodetectors. A dark current of the device can be reduced to 10 –9 A/cm 2 by introducing a Eu oxide thin-film layer as a carrier blocking layer at the interface between transparent conducting oxide (TCO) and the TiO 2 layer, and the specific detectivity reaches 5.2 × 10 15 jones at 365 nm with −3 V. The performance of our organic–inorganic hybrid photodetector surpasses those of existing ultraviolet photodetectors.