Organic Photodetectors with Gain and Broadband/Narrowband Response under Top/Bottom Illumination Conditions

Abstract Organic photodetectors (OPDs) possessing broadband/narrowband photodetection capability and gain have great potential in integrated optoelectronics products. In this work, OPDs with a device structure of ITO/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/thick active layer/semitransparent Al electrode exhibit the extraordinary functions, gain and bidirectional photodetection capability with tunable spectral response range. For the binary OPDs with poly(3‐hexylthiophene‐2,5‐diyl) (P3HT):[6,6]‐phenyl‐C 71 ‐butyric acid methyl ester (PC 71 BM) (100:1, wt/wt) as active layer, the OPDs exhibit narrowband response from 620 to 700 nm with full‐width at half maximum (FWHM) of ≈30 nm under bottom illumination condition and broadband response from 300 to 700 nm under top illumination condition, respectively. To further confirm and optimize the extraordinary functions of OPDs, ternary devices are fabricated with P3HT:poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dit‐hiophene‐co‐3‐fluor‐othieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):PC 71 BM (50:50:1, wt/wt) as active layer. The narrowband response can be adjusted to near infrared (NIR) region from 760 to 860 nm. The broadband response can be extended to NIR region with response range from 300 to 860 nm. Meanwhile, external quantum efficiency (EQE) spectral shape of the ternary OPDs becomes flatter under top illumination condition and can be kept constant under different bias. The ternary OPDs exhibit similar EQE values of ≈2000% and specific detectivity larger than 10 11 Jones at −50 V bias under bottom and top illumination conditions.