Photomultiplication-Type All-Polymer Photodetectors with a Signal-to-Noise Ratio over 118,800

Photomultiplication (PM) type all-polymer photodetectors (PM-APPDs) were fabricated by using polymer donor P3HT and polymer acceptor PY-IT as the photoactive layers. An optimal weight ratio of P3HT to PY-IT is approximately 100:4 to achieve an efficient hole transport channel and numerous isolated electron traps formed by P3HT/PY-IT/P3HT. These active layers exhibit hole-only transport characteristics, resulting in a low dark-current density (JD) of PM-APPDs. And JD of the PM-APPDs can be further suppressed by employing a triphenylamine-based cationic conjugated polyelectrolyte, TPAFA-7Br, as a hole transport layer (HTL) instead of a PEDOT:PSS layer. The optimal PM-APPDs with TPAFA-7Br as HTL display a rather low JD of 1.8 × 10–9 A·cm–2 under −10 V bias, which is significantly lower than the 2.1 × 10–6 A·cm–2 for PM-APPDs with PEDOT:PSS as HTL under the same bias. Additionally, the optimal PM-APPDs display an external quantum efficiency (EQE) of 1760% and a specific detectivity (D*shot) of 0.9 × 1014 Jones at 630 nm under 0.6 mW·cm–2 white light illumination. The resulting linear dynamic range of the optimal PM-APPDs is 122 dB, exhibiting a significant improvement compared to 106 dB for PM-APPDs with PEDOT:PSS as HTL. The signal-to-noise ratio of the optimized PM-APPDs reaches 118,800 under −10 V bias and 0.6 mW·cm–2 white light illumination, which should be among the best values for organic photodetectors without an additional current amplifier.