Low dark current inverted organic photodiodes using anionic polyelectrolyte as a cathode interlayer

We demonstrate the effect of anionic polyelectrolyte as a cathode interlayer to enhance charge selectivity of the electrode/semiconductor junction of organic photodiodes. Poly(styrenesulfonate) (PSS) was used as a cathode interlayer to tune the energy level of an ITO/ZnO electrode, so that hole injection can be minimized while electron extraction can be maximized. Optimized photodiodes with a PSS interlayer showed lower and flatter dark current density curves compared to the reference devices, which implies that tunneling currents at the electrode/active layer interface were dramatically suppressed. Moreover, PSS as an interlayer enabled lower charge recombination yield, as confirmed by the ideality factor and linear dynamic range analysis. As a result, we could realize the near-ideal organic photodiodes with a high performance of specific detectivity up to 3.3 × 1012 Jones at −5 V.