Image-Force Lowering Effect in Polymer Photodetectors

Recently, solution-processed polymer photodetectors (PDs) have attracted great attention in both academic and industrial sectors due to their advanced features compared with PDs based on traditional inorganic semiconductors. To achieve polymer PDs with a high external quantum efficiency (EQE) and ultrahigh detectivity (D*), the trap-assisted photomultiplication (PM) effect that takes place in the depletion region is applied in polymer PDs. However, the distribution of electron acceptors adjacent to the electrodes and the work function of the cathodes that affect the PM effect in polymer PDs are not well studied. In this study, the “image-force” affected by the distribution of electron acceptors and metal cathodes is used to investigate the PM effect in polymer PDs. Our studies reveal that the trapping of electrons varies along with the concentration of electron acceptors, which affects the PM effect. The PM effect is also influenced by the work function of the metal cathodes and applied reverse bias. Moreover, by using Au as the cathode, an EQE of over 17000% and D* over 1012 Jones are observed from polymer PDs under a reverse bias of −8 V. Our studies indicate that understanding the image-force-lowering effect is critical to achieving high device performance in PM-dominated polymer PDs.