Jinfeng Han

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.

Naphthalene diimide–diketopyrrolopyrrole copolymers as non-fullerene acceptors for use in bulk-heterojunction all-polymer UV–NIR photodetectors

A series of random copolymers containing the two electron-withdrawing units naphthalene diimide (NDI) and diketopyrrolopyrrole (DPP) and a thiophene (T) spacer were designed and synthesized as non-fullerene acceptors for all-polymer photodetectors. Increasing the number of DPP–T segments in the polymer backbone leads to a significant red shift in maximal absorption, bandgap narrowing, better film morphology and lower dark current density. A specific detectivity over 1012 Jones in a broad spectral region of 340–960 nm under −0.1 V bias was achieved with a photodetector using a blend of a donor polymer based on dithienopyrrole and diketopyrrolopyrrole (PDTP–DPP) and a copolymer (PNDI–DPP10) as an acceptor. In comparison, the device performance was found to be better than for the one based on PDTP–DPP and the PNDI homopolymer.

Side-chain engineering for fine-tuning of molecular packing and nanoscale blend morphology in polymer photodetectors

A series of four low-bandgap polymers containing diketopyrrolopyrrole (DPP) and dithienopyrrole (DTP) functionalized with four different side chains of 4-phenyl, 4-octylphenyl, 4-(octyloxy)phenyl and 4-(octylthio)phenyl were synthesized. Subtle changes in the side chains of polymers are found to effectively affect the molecular stacking and crystallinity, film morphology, and photodetector performance. The best polymer photodetector displays an average external quantum efficiency (EQE) of 40% and a specific detectivity (D*) of over 1013 Jones in the spectral region of 350–960 nm under −0.1 V bias, which is among the best EQE and D* values of all the known UV–vis–NIR polymer photodetectors reported to date.

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.

Side-chain engineering in naphthalenediimide-based n-type polymers for high-performance all-polymer photodetectors

A series of n-type semiconducting conjugated polymers based on naphthalene diimide (NDI) having three different side chains, 5-decylpentadecyl, 2-octyldodecyl and 4-(2-octyldodecyloxy)phenyl, were synthesized. Experimental results showed that the subtle structural changes at the side chains can influence the molecular packing, electron mobility, blend film morphology and thus performance of bulk-heterojunction polymer photodetectors using these NDI-based polymers as acceptors. The optimized all-polymer photodetector exhibited a specific detectivity (D*) of over 1013 Jones in the spectral region of 300–800 nm under −0.1 V bias, which is among the best D* values of the reported UV–vis–NIR all-polymer photodetectors and comparable to the best fullerene-based photodetectors.

Low-LUMO acceptor polymers for high-gain all-polymer photodiodes

In this work, we report three acceptor polymers with low levels of lowest unoccupied molecular orbital (LUMO) energies and studies on all-polymer photodiodes. By employing these polymers as electron acceptors and PTB7-Th as electron donors, we prepared all-polymer photodiodes that exhibited a high gain in external quantum efficiency (EQE) and high detectivity. In particular, P3-based devices showed EQE over 40 000%, responsivity over 110 A W−1 and a specific detectivity of 3.5 × 1014 Jones, representing the best result of all-polymer photodiodes reported to date. Our work has demonstrated that high gain all-polymer photodiodes could be readily achieved by using appropriate interlayers and low-LUMO acceptor polymers.