Zhenjie Ni

A Retina-Like Dual Band Organic Photosensor Array for Filter-Free Near-Infrared-to-Memory Operations

Human eyes use retina photoreceptor cells to absorb and distinguish photons from different wavelengths to construct an image. Mimicry of such a process and extension of its spectral response into the near-infrared (NIR) is indispensable for night surveillance, retinal prosthetics, and medical imaging applications. Currently, NIR organic photosensors demand optical filters to reduce visible interference, thus making filter-free and anti-visible NIR imaging a challenging task. To solve this limitation, a filter-free and conformal, retina-inspired NIR organic photosensor is presented. Featuring an integration of photosensing and floating-gate memory modules, the device possesses an acute color distinguishing capability. In general, the retina-like photosensor transduces NIR (850 nm) into nonvolatile memory and acts as a dynamic photoswitch under green light (550 nm). In doing this, a filter-free but color-distinguishing photosensor is demonstrated that selectively converts NIR optical signals into nonvolatile memory.

Quinoline‐Flanked Diketopyrrolopyrrole Copolymers Breaking through Electron Mobility over 6 cm2 V−1 s−1 in Flexible Thin Film Devices

Herein, the design and synthesis of novel π-extended quinoline-flanked diketopyrrolopyrrole (DPP) [abbreviated as QDPP] motifs and corresponding copolymers named PQDPP-T and PQDPP-2FT for high performing n-type organic field-effect transistors (OFETs) in flexible organic thin film devices are reported. Serving as DPP-flankers in backbones, quinoline is found to effectively tune copolymer optoelectric properties. Compared with TDPP and pyridine-flanked DPP (PyDPP) analogs, widened bandgaps and strengthened electron deficiency are achieved. Moreover, both hole and electron mobility are improved two orders of magnitude compared to those of PyDPP analogs (PPyDPP-T and PPyDPP-2FT). Notably, featuring an all-acceptor-incorporated backbone, PQDPP-2FT exhibits electron mobility of 6.04 cm2 V-1 s-1 , among the highest value in OFETs fabricated on flexible substrates to date. Moreover, due to the widened bandgap and strengthened electron deficiency of PQDPP, n-channel on/off ratio over 105 with suppressed hole transport is first realized in the ambipolar DPP-based copolymers.

Asymmetric thiophene/pyridine flanked diketopyrrolopyrrole polymers for high performance polymer ambipolar field-effect transistors and solar cells

Two novel asymmetric thiophene/pyridine flanked diketopyrrolopyrrole (DPP) based polymers, named PPyTDPP-TT and PPyTDPP-BT were designed, synthesized and applied in organic field-effect transistors (OFETs) and polymer solar cells (PSCs). In contrast to the reported bipyridine flanked DPP, the asymmetric DPP polymers incorporating thiophene/pyridine flankers exhibited narrower bandgaps of ∼1.5 eV and deeper HOMO energy levels, thus leading to a broadened absorption from 500 to 850 nm and were potentially beneficial for low-energy photon harvesting. Both polymers displayed promising ambipolar semiconducting properties. The hole and electron mobilities of PPyTDPP-TT reach 0.48 cm2 V−1 s−1 and 0.18 cm2 V−1 s−1; and PPyTDPP-BT reach 0.55 cm2 V−1 s−1 and 0.08 cm2 V−1 s−1, respectively. Intriguingly, due to their ambipolar properties, two polymers can play an ambipolar role, both as electron donors and acceptors with PC71BM and P3HT in PSCs. Photovoltaic devices based on PPyTDPP-BT as the donor material reach PCEs of 7.56% and achieve 0.59% as the acceptor material, while those based on PPyTDPP-TT reach 5.48% with PC71BM and 0.82% with P3HT, respectively. These results suggest that the adoption of asymmetric flanker DPP polymers can effectively tune the absorption properties of polymers as excellent ambipolar transporting polymers towards high performance in both OFETs and PSCs.

Versatile asymmetric thiophene/benzothiophene flanked diketopyrrolopyrrole polymers with ambipolar properties for OFETs and OSCs

Three novel asymmetric thiophene/benzothiophene-flanked diketopyrrolopyrrole (DPP)-based polymers with different π bridges, designated as PBTTDPP-BT, PBTTDPP-TT and PBTTDPP-2FBT, were designed, synthesized and employed in organic solar cells. Compared with the reported thiophene/pyridine-flanked DPP, these thiophene/benzothiophene-flanked DPP polymers exhibited narrower band gaps below 1.5 eV, leading to a broadened absorption that ranged from 500 nm to 850 nm. All polymers displayed promising ambipolar semiconducting properties. PBTTDPP-BT, PBTTDPP-TT and PBTTDPP-2FBT showed hole mobilities of 1.20, 1.68 and 1.50 cm2 V−1 s−1, respectively. Their corresponding electron mobilities were 0.40, 0.14 and 0.35 cm2 V−1 s−1. Interestingly, PBTTDPP-TT and PBTTDPP-2FBT also showed ambipolar properties in organic solar cells. Photovoltaic device based on PBTTDPP-TT as a donor material reached a power conversion efficiency (PCE) of 6.96% with PC71BM as an acceptor, while this device as the acceptor material achieved only 0.28% with poly(3-hexylthiophene) (P3HT) as the donor. In contrast, PCE of PBTTDPP-2FBT-based devices reached 5.62% with PC71BM and 0.44% with P3HT. These results suggest that the adoption of asymmetric flankers in DPP polymers can effectively tune their ambipolar transporting properties for high-performance organic electronic devices.

A new organic compound of 2-(2,2-diphenylethenyl)anthracene (DPEA) showing simultaneous electrical charge transport property and AIE optical characteristics

A new compound, 2-(2,2-diphenylethenyl) anthracene (DPEA), was designed and synthesized, which showed a hole carrier mobility of 0.66 cm2 V−1 s−1 and typical aggregated induced emission (AIE) behaviour with a ratio of 15 times, which is among the best performance of recently reported semiconducting AIE materials. This work not only enriches the AIE electronic material systems, but also initiates a new direction for developing high performance integrated optoelectronic organic semiconductors for potential multifunctional applications.

Halogen bonded cocrystal polymorphs of 1,4-di(4′-pyridyl)-1,3-diacetylene

Cocrystal polymorphs based on sym-triiodo-trifluorobenzene (IFB) with 1,4-di(4′-pyridyl)-1,3-diacetylene (DPDA) are formed with halogen bond interactions. Two cocrystal phases were obtained by using different solvents, acetonitrile and methylene chloride, and confirmed by their single crystal structure data. In the application direction, the different photo-physical properties of the two phases were discussed carefully.

An Asymmetric Furan/Thieno[3,2-b]Thiophene Diketopyrrolopyrrole Building Block for Annealing-Free Green-Solvent Processable Organic Thin-Film Transistors

A new asymmetric furan and thieno[3,2-b]thiophene flanked diketopyrrolopyrrole (TTFDPP) building block for conjugated polymers is designed and used to generate a donor-acceptor semiconducting polymer, poly[3-(furan-2-yl)-2,5-bis(2-octyldodecyl)-6-(thieno[3,2-b]thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-thieno[3,2-b]thiophene] (abbreviated to PTTFDPP-TT), consisting of TTFDPP unit copolymerized with thieno[3,2-b]thiophene comonomer (TT), which is further synthesized. Results demonstrate that PTTFDPP-TT-based thin-film transistors in a bottom-gate bottom-contact device configuration exhibit typical hole-transporting property, with weak temperature dependence for charge carrier mobility from room temperature to 200 °C. In addition, the good solubility of PTTFDPP-TT due to the incorporation of a polar furan unit and an asymmetric conjugated structure makes it able to be solution processed with a less toxic nonchlorinated solvent such as toluene, demonstrating comparable performance with that prepared from chlorinated solution. These results suggest PTTFDPP-TT as a promising organic semiconductor candidate for annealing-free, environmentally benign, and less energy-consuming applications in large-area flexible organic electronic devices.

A Ferroelectric/Electrochemical Modulated Organic Synapse for Ultraflexible, Artificial Visual‐Perception System

Human eyes undertake the majority of information assimilation for learning and memory. Transduction of the color and intensity of the incident light into neural signals is the main process for visual perception. Besides light-sensitive elements that function as rods and cones, artificial retinal systems require neuromorphic devices to transform light stimuli into post-synaptic signals. In terms of plasticity timescale, synapses with short-term plasticity (STP) and long-term potentiation (LTP) represent the neural foundation for experience acquisition and memory formation. Currently, electrochemical transistors are being researched as STP-LTP devices. However, their LTP timescale is confined to a second-to-minute level to give unreliable non-volatile memory. This issue limits multiple-plasticity synapses with tunable temporal characteristics and efficient sensory-memory systems. Herein, a ferroelectric/electrochemical modulated organic synapse is proposed, attaining three prototypes of plasticity: STP/LTP by electrochemical doping/de-doping and ferroelectric-LTP from dipole switching. The device supplements conventional electrochemical transistors with 10000-second-persistent non-volatile plasticity and unique threshold switching properties. As a proof-of-concept for an artificial visual-perception system, an ultraflexible, light-triggered organic neuromorphic device (LOND) is constructed by this synapse. The LOND transduces incident light signals with different frequency, intensity, and wavelength into synaptic signals, both volatile and non-volatile.

Enhanced stability of a rubrene analogue with a brickwork packing motif

In this study, a rubrene analogue (SF10-RUB) was designed and synthesised. Due to the introduction of pentafluorobenzene into the molecular structure, the packing motif of this material changed from a nonclassical herringbone packing to a brickwork packing. Moreover, intermolecular interactions, including C–H⋯π, S⋯F, C–H⋯F, and F⋯H interactions, were much more in SF10-RUB than those in its courterpart (SF0-RUB and RUB), together with its lower HOMO level, which made this material much more stable than other materials.