Ji Qi

Advances in Organic Near-Infrared Materials and Emerging Applications

Much progress has been made in the field of research on organic near-infrared materials for potential applications in photonics, communications, energy, and biophotonics. This account mainly describes our research work on organic near-infrared materials; in particular, donor-acceptor small molecules, organometallics, and donor-acceptor polymers with the bandgaps less than 1.2 eV. The molecular designs, structure-property relationships, unique near-infrared absorption, emission and color/wavelength-changing properties, and some emerging applications are discussed.

Low-bandgap donor–acceptor polymers for photodetectors with photoresponsivity from 300 nm to 1600 nm

A novel donor unit dithienobenzotrithiophen (DTBTT) was designed and utilized in the synthesis of a series of donor–acceptor (D–A) polymers with the thienoisoindigo-based acceptor. The relationships between the structure of polymers and the absorption spectra, electrochemistry properties, hole mobility, and photovoltaic properties of these polymers have been studied. The results showed that low-bandgap D–A polymers containing DTBTT are suitable for use in broadband polymer photodetectors. Polymer photodetectors exhibited a specific detectivity (D*) in the order of 1012 Jones, low dark current and photoresponsivity at the wavelengths from 300 to 1600 nm.

Significant enhancement of photodetector performance by subtle changes in the side chains of dithienopyrrole-based polymers

A pair of analogous polymers based on diketopyrrolopyrrole (DPP) and dithienopyrrole (DTP) were designed to have a small structural difference in the side chain, PDDPDTP-C with an alkyl chain and PDPPDTP-P with an alkylphenyl chain. The two polymers have the same absorption and band gap but show different hole mobility, molecular stacking and film morphology. As a result, the PDPPDTP-P photodetector has a much higher responsivity (291 mA W−1 at 900 nm at −0.1 V) than the one based on PDDPDTP-C (36 mA W−1), and exhibits a specific detectivity over 1012 Jones in the spectral region of 350–950 nm.

Hierarchical manipulation of uniform multi-nanoparticles by electrochemical coupling assembly

Assembling multiple nanomaterials into a single nanostructure is a promising way to obtain a multifunctionality derived from each building block. We address here the need for a general all-solution processed strategy to control the fabrication of multiple nanoparticles (NPs) at room temperature and under vacuum free conditions. The monodisperse multiple NPs were integrated successively into thin bulk-hybrid gradient or periodic tandem multilayer films through tuning the cycling number of cyclic voltammetry (CV), which are based on the quantitatively electrochemical deposition of each type of NPs thanks to the electrochemical coupling reaction of the N-alkylcarbazole ligand. This simple method yields nanoporous, transparent, stable and photoactive films with a hierarchical structure of multiple uniform NPs, exemplified by the prototype photodetector devices. Significantly, this strategy opens an avenue to fabricate low-cost wire and 3-dimensional NPs films on physically flexible conducting substrates.