Achieving Reliable Detectivity in Photomultiplication-Type Organic Photodetectors Using an AZO Interface Layer

A photomultiplication (PM)-type organic photodetector with ITO/AZO/P3HT:PC61BM (100:1)/Al as the device structure is fabricated to achieve reliable detectivity in broadband detection. Here, we employ a cost-effective sol–gel spin coating method to deposit AZO thin films, which serve as the interface layer, while P3HT:PC61BM (100:1) acts as the active layer. Post UV illumination, the optimized AZO-based PM OPD aids in reducing carrier injection from ITO at the AZO/ITO interface. This suppresses the variation in the dark current before and after irradiation conditions. For pristine ZnO-based PM OPD at −5 V applied bias, the dark current density increased from 17.9 to 63.5 μA/cm2 after irradiation and took more than 3 h to reach the OFF state, whereas for optimized AZO, a minimal change in the dark current density was observed, from 1.09 to 1.2 μA/cm2, under the same conditions and it reached the OFF state in only 514 ms. The AZO-based PM OPD showed a broad spectral response from 350 to 700 nm with a maximum EQE of 903%, a responsivity of 4.3 A/W, and a detectivity of 1012 Jones at 590 nm under −5 V applied bias. This study realizes stable PM-type broadband photodetectors with potential applications in the field of imaging and surveillance.