On the origin of dark current in organic photodiodes

\u3cp\u3eMinimizing the reverse bias dark current while retaining external quantum efficiency is crucial if the light detection sensitivity of organic photodiodes (OPDs) is to compete with inorganic photodetectors. However, a quantitative relationship between the magnitude of the dark current density under reverse bias (J\u3csub\u3ed\u3c/sub\u3e) and the properties of the bulk heterojunction (BHJ) active layer has so far not been established. Here, a systematic analysis of J\u3csub\u3ed\u3c/sub\u3e in state-of-the-art BHJ OPDs using five polymers with a range of energy levels and charge transport characteristics is presented. The magnitude and activation energy of J\u3csub\u3ed\u3c/sub\u3e are explained using a model that assumes charge injection from the metal contacts into an energetically disordered semiconductor. By relating J\u3csub\u3ed\u3c/sub\u3e to material parameters, insights into the origin of J\u3csub\u3ed\u3c/sub\u3e are obtained that enable the future selection of successful OPD materials.\u3c/p\u3