Establishing multi-colour patterning technology for colloidal quantum dots is critical for realising high-resolution displays based on the material. Here, we report a solution-based processing method ...to form patterns of quantum dots using a light-driven ligand crosslinker, ethane-1,2-diyl bis(4-azido-2,3,5,6-tetrafluorobenzoate). The crosslinker with two azide end groups can interlock the ligands of neighbouring quantum dots upon exposure to UV, yielding chemically robust quantum dot films. Exploiting the light-driven crosslinking process, different colour CdSe-based core-shell quantum dots can be photo-patterned; quantum dot patterns of red, green and blue primary colours with a sub-pixel size of 4 μm × 16 μm, corresponding to a resolution of >1400 pixels per inch, are demonstrated. The process is non-destructive, such that photoluminescence and electroluminescence characteristics of quantum dot films are preserved after crosslinking. We demonstrate that red crosslinked quantum dot light-emitting diodes exhibiting an external quantum efficiency as high as 14.6% can be obtained.
Recently, near infrared (NIR) organic photodetectors (OPDs) have been extensively studied. Bulk heterojunction NIR OPDs composed of a high-bandgap polymer donor (PD) and a low-bandgap non-fullerene ...acceptor (NFA) showed the best performance, whereas the low-bandgap PD-based OPDs were relatively unsuccessful due to the high level of dark current density (Jd) under a negative bias. In this study, we synthesized three low-bandgap PDs based on a thieno3,4-bpyrazine (TP) moiety and developed red-NIR OPDs by blending them with a low-bandgap NFA. We found that the PD having a shallow HOMO energy level generated the largest ground-state electron transfer at negative bias, which overestimated the responsivity (R) and detectivity (D*) in OPDs. Notably, under weak light irradiation of 0.1 mW/cm2 at -2V, the contribution of Jd on Jph reached 99.6%. Thus, we modified the existing R and D* equations to better understand photodetecting properties at low light intensity, and these modified equations gave more realistic R and D* values in OPDs. On the other hand, a low-bandgap PD showing low Jd in OPDs was highly beneficial to detect a low light signal because the Jd negligibly contributed to Jph in OPDs. The low Jd values of OPDs at negative bias resulted in a high on/off signal ratio and constant R and D* values at different light intensities.
Three low bandgap conjugated polymers, PBTTP, PCTTP and PDTTP, based on thieno3,4-bpyrazine (TP) were developed and studied for red and near-infrared organic photodetectors (OPDs). The dark current density (Jd) was highly important at weak light irradiation and the contributions of Jd on photocurrent density were analyzed and discussed. Display omitted
•Three novel thieno3,4-bpyrazine-based low bandgap polymers were synthesized.•Red-NIR photodetectors were fabricated and contribution of dark current density (Jd) was investigated.•Shallow HOMO energy levels and disordered p-n junction morphology generated a high level of Jd.•The Jd should be carefully considered not to overestimate responsivity and detectivity.
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•Environmentally friendly Pb-free QPDs were reported by utilizing AgBiS2 NCs.•A novel CPE increased D* of QPDs by 3–4.5 times higher than that without CPE.•The ultrafast response time ...of 1.0 μs were achieved under 680 nm red light.•The promising D* of 1.4 × 1012 Jones at −0.5 V was achieved under 680 nm light.•The highest D* values and fastest response time were reported among the AgBiS2 QPDs.
Lead-free quantum-dot photodetectors (QPDs) are currently the subject of research interest due to the environmental threat posed by lead, but relatively poor photodetection ability has been reported so far. Here, we develop high-performance AgBiS2 nanocrystal (NC)-based QPDs with a responsivity (R) of 0.55 A/W and detectivity (D*) of 1.4 × 1012 Jones at −0.5 V under a 680 nm LED light (1.0 mW/cm2) by incorporating a novel conjugated polyelectrolyte (CPE) as a cathode buffer layer (CBL) on the surface of the electron transporting layer (ETL). The CPE was developed by co-polymerization of bromohexyl-substituted fluorene and pyrene rings, followed by quaternization with trimethylamine at the terminal alkyl chains. The synthesized CPE decreased the work function and reduced the number of trap sites at the ETL surface, which increased photocurrent density and reduced dark current density, resulting in a D* value by 3 to 4.5 times greater than that without CPE treatment. Our AgBiS2 NC-based QPDs achieved ultrafast rising and falling response times of 1.0 and 3.2 μs, respectively, under the 680 nm LED light, and the CBL layer was able to rapidly remove residual current density in the off-light state, improving the dynamic characteristics of AgBiS2 QPDs under near-infrared light (940 nm).
Colloidal quantum dots (QDs) stand at the forefront of a variety of photonic applications given their narrow spectral bandwidth and near-unity luminescence efficiency. However, integrating ...luminescent QD films into photonic devices without compromising their optical or transport characteristics remains challenging. Here we devise a dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands to enable QDs to be universally compatible with solution-based patterning techniques. The successful control over the structure of both ligands allows the direct patterning of dual-ligand QDs on various substrates using commercialized photolithography (i-line) or inkjet printing systems at a resolution up to 15,000 pixels per inch without compromising the optical properties of the QDs or the optoelectronic performance of the device. We demonstrate the capabilities of our approach for QD-LED applications. Our approach offers a versatile way of creating various structures of luminescent QDs in a cost-effective and non-destructive manner, and could be implemented in nearly all commercial photonics applications where QDs are used.
Recently, all-polymer-based p–n bulk heterojunction organic photodiodes exhibited a high photocurrent density (J ph) through the state-of-the-art synthesis in n-type conjugated polymers. However, in ...the organic photodetector (OPD) application, the on–off ratio (J ph/dark current density (J d)) is a performance-determining parameter; thus herein we focused on effectively increasing the on–off ratio by lowering the J d of all-polymer OPDs. We developed four n-type polymers, with nonconjugated spacers, which effectively suppressed the J d of the devices; the increased insulating properties and excellent hole-blocking properties under dark conditions aided J d suppression. Moreover, breaking the π-conjugation of the n-type polymers, by adding short bulky nonconjugated spacers, effectively increased J ph and decreased J d in relation with those upon the addition of long flexible alkyl spacers. Hence, the OPDs based on the n-type polymer with a nonconjugated spacer exhibited a high specific detectivity of >1012 Jones and a −3 dB cutoff frequency of 219 kHz. Notably, they also displayed ultrafast rising and falling response times of 2 and 9 μs, respectively, at −2 V.
Suppressing the dark current density (J d) while maintaining sufficient charge transport is important for improving the specific detectivity (D*) and dynamic characteristics of organic photodetectors ...(OPDs). In this study, we synthesized three novel small-molecule acceptors (SMAs) densely surrounded by insulating alkyl side chains to minimize the J d in OPDs. Introducing trialkylated N-annulated perylene diimide as a terminal moiety to the alkylated π-conjugated core structure was highly efficient in suppressing J d in the devices, resulting in an extremely low J d of 4.60 × 10–11 A cm–2 and 10–100 times improved D* values in the devices. In addition, SMAs with a geometrically aligned backbone structure exhibited better intermolecular ordering in the blended films, resulting in 3–10 times as high responsivity (R) values in the OPDs. Outstanding OPD performances with a D* of 8.09 × 1012 Jones, −3 dB cutoff frequency of 205.2 kHz, and rising response time of 16 μs were achieved under a 530 nm illumination in photoconductive mode. Geometrically aligned core-terminal SMAs densely surrounded by insulating alkyl side chains are promising for improving the static and dynamic properties of OPDs.
Porphyrin-based photodiode materials have mainly been targeted to achieve panchromatic absorption by maximizing the Soret- and Q-band absorption; however, they have rarely been studied with the ...purpose to make them wavelength-selective in photodetecting devices. In this study, we synthesized a wavelength-selective porphyrin material, PZn-FL, via Sonogashira coupling between an ethyne π-linked porphyrin core (PZn) and four fluorene (FL) moieties. The synthesized PZn-FL material showed a narrow full-width-at-half-maximum (FWHM) of 75 nm in the blue absorption region. The Q-band absorption of PZn-FL was significantly suppressed in organic photodiodes (OPDs), resulting in a blue-selective specific detectivity spectrum with a FWHM of 75 nm and a noise equivalent power of 2.86 × 10−12 W/Hz0.5. The planar backbone structure of PZn-FL was beneficial to increase charge transport and reduce bimolecular recombination, and the vertically oriented alkyl side chains of the PZn backbone contributed to prevent severe intermolecular aggregation and maintain a narrow absorption in film state.
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•We synthesized a wavelength-selective porphyrin material, PZn-FL.•PZn-FL showed a narrow full-width-at-half-maximum (FWHM) of 75 nm in film states.•A blue-selective specific detectivity with a FWHM of 75 nm was also achieved in OPDs.•The planar backbone of PZn-FL with vertically oriented alkyl side chains was key structure.
Rechargeable organic batteries show great potential as a low-cost, sustainable and mass-producible alternatives to current transition-metal-based cells; however, serious electrode dissolution issues ...and solubilization of organic redox intermediates (shuttle effect) have plagued the capacity retention and cyclability of these cells. Here we report on the use of a metal-organic framework (MOF) gel membrane as a separator for organic batteries. The homogeneous micropores, intrinsic of the MOF-gel separator, act as permselective channels for targeted organic intermediates, thereby mitigating the shuttling problem without sacrificing power. A battery using a MOF-gel separator and 5,5'-dimethyl-2,2'-bis-p-benzoquinone (Me
BBQ) as the electrode displays high cycle stability with capacity retention of 82.9% after 2,000 cycles, corresponding to a capacity decay of ~0.008% per cycle, with a discharge capacity of ~171 mA h g
at a current density of 300 mA g
. The molecular and ionic sieving capabilities of MOF-gel separators promise general applicability, as pore size can be tuned to specific organic electrode materials. The use of MOF-gel separators to prevent side reactions of soluble organic redox intermediates could lead to the development of rechargeable organic batteries with high energy density and long cycling life.
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