Achieving Reliable\nDetectivity in Photomultiplication-Type\nOrganic Photodetectors Using an AZO Interface Layer

A photomultiplication (PM)-type organic\nphotodetector\nwith ITO/AZO/P3HT:PC<sub>61</sub>BM (100:1)/Al as the device structure\nis fabricated to achieve\nreliable detectivity in broadband detection. Here, we employ a cost-effective\nsol–gel spin coating method to deposit AZO thin films, which\nserve as the interface layer, while P3HT:PC<sub>61</sub>BM (100:1)\nacts as the active layer. Post UV illumination, the optimized AZO-based\nPM OPD aids in reducing carrier injection from ITO at the AZO/ITO\ninterface. This suppresses the variation in the dark current before\nand after irradiation conditions. For pristine ZnO-based PM OPD at\n−5 V applied bias, the dark current density increased from\n17.9 to 63.5 μA/cm<sup>2</sup> after irradiation and took more\nthan 3 h to reach the OFF state, whereas for optimized AZO, a minimal\nchange in the dark current density was observed, from 1.09 to 1.2\nμA/cm<sup>2</sup>, under the same conditions and it reached\nthe OFF state in only 514 ms. The AZO-based PM OPD showed a broad\nspectral response from 350 to 700 nm with a maximum EQE of 903%, a\nresponsivity of 4.3 A/W, and a detectivity of 10<sup>12</sup> Jones\nat 590 nm under −5 V applied bias. This study realizes stable\nPM-type broadband photodetectors with potential applications in the\nfield of imaging and surveillance.