High sensitivity and fast response solution processed polymer photodetectors with polyethylenimine ethoxylated (PEIE) modified ITO electrode.

Most organic photodetectors utilize a bulk heterojunction (BHJ) photo-active film due to its high exciton dissociation efficiency. However, the low dark current density, a key role in determining the overall performance of photodetectors, is hardly achieved in the BHJ structure since both the donor and acceptor domains are in contact with the same electrode. The most popular strategy to overcome this problem is by fabricating bilayer or multilayer devices. However, the complicated fabrication process is a challenge for printing electronics. In this work, we demonstrate a solution processed polymer photodetector based on a poly (3-hexylthiophene) (P3HT): (phenyl-C61-butyric-acid-methyl-ester) (PC₆₁BM) blend film with polyethylenimine ethoxylated (PEIE) modified ITO electrode. The transparent PEIE efficiently blocks the unnecessary electronic charge injection between the active film and the electrode, which dramatically decrease the dark current. Under illumination, the photoexcited charges accumulated in the PEIE modified ITO region finally can tunnel through the barrier with the help of the applied reverse bias, leading to a large photocurrent. Therefore, the resulting polymer photodetector shows a 2.48 × 10⁴ signal-to-noise ratio (SNR) under -0.3 V bias and an 11.4 MHz bandwidth across the visible spectra under a small reverse bias of 0.5 V. The maximum EQE of 3250% in the visible wavelength is obtained for the polymer photodetector at -1 V under 370 nm (3.07 μW/cm²) illumination. This solution processed polymer photodetector manufacturing is highly compatible with the flexible, low-cost, and large area organic electronic technologies.