Smart Strategy: Transparent Hole-Transporting Polymer as a Regulator to Optimize Photomultiplication-type Polymer Photodetectors

Photomultiplication-type polymer photodetectors (PM-PPDs) were fabricated with hole-only transport active layers containing polymer(s): [6,6]-phenylC61-butyric acid methyl ester (PC₆₁BM) with a weight ratio of 100:2. The rather less PC₆₁BM content in active layers prefers to generate a large amount of isolated electron traps surrounded by polymers. Photogenerated electrons prefer to be trapped by the isolated PC₆₁BM due to the lack of continuous electron-transport channels. The trapped electrons by the isolated PC₆₁BM close to the Al electrode would like to seduce hole tunneling injection. The transparent polymer poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] (poly-TPD) was incorporated as a regulator to improve hole mobility (μ_h) and adjust the trapped-electron distribution in active layers, leading to the enhanced performance of PM-PPDs. The optimal PM-PPDs were achieved using poly(3-hexylthiophene) (P3HT):poly-TPD:PC₆₁BM (80:20:2, wt/wt/wt) as active layers. External quantum efficiency (EQE) values at 620 nm are 3900 and 1250% for PM-PPDs based on P3HT:poly-TPD:PC₆₁BM (80:20:2, wt/wt/wt) and P3HT:PC₆₁BM (100:2, wt/wt) under -10 V applied voltage, respectively. The EQE at 620 nm of optimal PM-PPDs is improved from 650 to 63,000% along with the applied voltage increase from -5 to -20 V. This work provides a new strategy of using transparent polymer with large μ_h as a regulator for EQE and response speed improvement, as well as the flattened EQE spectral shape of PM-PPDs.