High-detectivity organic photodetectors based on a thick-film photoactive layer using a conjugated polymer containing a naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole unit

In this study, we fabricated a bulk-heterojunction organic photodetector with high detectivity by using a naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole-based narrow-bandgap π-conjugated polymer of PNTT as the donor and a fullerene derivative PC₇₁BM as the acceptor. The relatively high mobility of PNTT allows the construction of a thick-film photoactive layer, which results in an increase in external quantum efficiency and a dramatic reduction in the dark current density. The combination of these advantages leads to an obvious increase in the detectivity and enhanced film thickness. A device based on a film thickness of 400 nm exhibited a very low dark current density of 0.33 nA cm⁻² and rectification in the order of 10⁵ in the range of ±2 V. The resulting device exhibited high detectivity exceeding 10¹³ cm Hz^1/2 W⁻¹ in the range of 350 to 800 nm, with a maximum detectivity of 4.00 × 10¹³ cm Hz^1/2 W⁻¹ and a responsivity of 0.4 A W⁻¹ at a working wavelength of 760 nm under a reverse bias of −0.1 V, which is among the highest values reported so far for organic photodetectors at this working wavelength without extra gains.