Development of special organic materials that are able to absorb light energy in the second near-infrared window (NIR-II) is significantly important for treating deep-tissue-buried diseases or ...supplying power to implantable electronic devices. Herein, a narrow bandgap donor–acceptor (D-A) conjugated polymer with thiophene-fused benzodifurandione-based oligo(p-phenylenevinylene) (TBDOPV) as acceptor part and 2,2′-bithiophene (DT) as donor part was developed and exploited as a photothermal conversion material with high extinction coefficient and robust photostability in the NIR-II window. According to transient absorption analysis results, the photothermal conversion ability of this polymer is attributed to the fast internal conversion (IC) process. The high photothermal conversion efficiency makes this polymer a promising NIR-II adsorbing antenna to remotely actuate thermo-dependent devices, e.g., high-performance photothermal–electrical and photothermal–mechanical converters.
Colloidal quantum dots (QDs) have demonstrated great promise in artificial photosynthesis. However, the ultrasmall size hinders its controllable and effective interaction with cocatalysts. To improve ...the poor interparticle electronic communication between free QD and cocatalyst, we design here a self-assembled architecture of nanoparticles, QDs and Pt nanoparticles, simply jointed together by molecular polyacrylate to greatly enhance the rate and efficiency of interfacial electron transfer (ET). The enhanced interparticle electronic communication is confirmed by femtosecond transient absorption spectroscopy and X-ray transient absorption. Taking advantage of the enhanced interparticle ET with a time scale of ∼65 ps, 5.0 mL of assembled CdSe/CdS QDs/cocatalysts solution produces 94 ± 1.5 mL (4183 ± 67 μmol) of molecular H2 in 8 h, giving rise to an internal quantum yield of ∼65% in the first 30 min and a total turnover number of >1.64 × 107 per Pt nanoparticle. This study demonstrates that self-assembly is a promising way to improve the sluggish kinetics of the interparticle ET process, which is the key step for advanced H2 photosynthesis.
Positively charged cationic defects deteriorate the performance and long-term stability of perovskite solar cells. Herein, a nitrogen-donor crown ether is introduced as a positive defect passivator. ...A high open-circuit voltage of 1.174 V, a superior fill factor of 82.15% and an efficiency of 24.07% are achieved. The PSCs exhibit enhanced operational, moisture and thermal stability.
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•A18C6 passivates positively charged cationic defects (Pb2+, Cs+) in perovskite.•Perovskite solar cells obtain a PCE of 24.07 % with a Voc of 1.174 V.•Operational, moisture and heat stabilities of films and devices are enhanced.
Positively charged cationic defects are the main source of defects in metal-halide perovskite solar cells. They determine the quasi-Fermi level of electrons under illumination and contribute to non-radiative recombination loss, causing an open-circuit voltage deficit. In addition, they act as ion migration pathways for halide hopping, thus deteriorating long-term stability. Herein, a nitrogen-donor crown ether as a positive defect passivator is developed, which demonstrates a soft Lewis base nature, a large donor number and a higher formation constant with positively charged cationic defects. Density functional theory calculation indicates that the electron-donating nitrogen atom dramatically increases the electron density of oxygen atoms, leading to a strong affinity with positively charged cationic defects (Pb2+ and Cs+). The electron trap density in perovskite is significantly reduced by 27 %, resulting in an increased build-in potential. By adding a small amount of nitrogen-donor crown ether to the precursor solution, the perovskite solar cells achieve an efficiency of 24.07 % with an open-circuit voltage of 1.174 V and a fill factor of 82.15 %. Moreover, the unencapsulated perovskite solar cells show a T80 lifetime of 510 h under continuous operation (1 sun equivalent illumination, maximum power point tracking condition, dry N2 atmosphere), and enhanced moisture and heat stability.
Benefiting from a deep tissue penetration and high allowed maximum exposure power, near-infrared (NIR)-II (1000-1350 nm) absorbers for photothermal conversion have received considerable attention in ...a myriad of fields. To promote specificity, introducing a stimuli-responsive behaviour provides a promising approach for achieving intelligent NIR-II photothermal conversion under varied environments. However, NIR-II absorbers are currently mostly constructed by conjugated polymers, which can hardly be modified with stimuli-responsive segments, while small molecular chromophores can be simply functionalized, yet their absorption bands are extremely limited by their short conjugation length. To address this inherent contradiction, a series of "turn-on" types of absorbers were developed with a two-stage superlarge redshifted absorption in the first and second NIR window under the stimulation of protonation. The mechanism of such bathochromic shift behaviours was further studied through EPR spectroscopy and DFT calculations. Under the irradiation of 808 nm and 1064 nm lasers, the photothermal conversion abilities could be switched on and off synchronously. We believe "turn-on" types of NIR-II absorbers will offer great inspiration for designing smart materials with controllable NIR-I and NIR-II photothermal conversion capabilities.
A series of "turn-on" type NIR materials are developed with two-stage superlarge redshifted absorption in the first and second NIR window under the stimulation of protonation for smart photothermal conversion.
Here we present a facile aqueous approach to synthesize heterostructured CdSe/CdS QDs with all-inorganic chalcogenide S 2− ligands under mild conditions. High-resolution transmission electron ...microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and steady-state emission spectroscopy demonstrate that the heterostructured CdSe/CdS QDs with sulfur-rich surface composition are formed by heterogeneous nucleation of Cd 2+ and S 2− precursors on the CdSe QDs. After adsorption of small Ni(OH) 2 clusters over the surface in situ , the CdSe/CdS–Ni(OH) 2 photocatalyst enables H 2 production efficiently with an internal quantum yield of 52% under visible light irradiation at 455 nm, up to an 8-fold increase of activity to that of spherical CdSe QDs–Ni(OH) 2 under the same conditions. Femtosecond transient absorption spectroscopy, X-ray transient absorption (XTA) spectroscopy, steady-state and time-resolved emission spectroscopy show that the quasi-type-II band alignment in the CdSe/CdS heterostructure is responsible for the efficiency enhancement of light harvesting and surface/interfacial charge separation in solar energy conversion. The unprecedented results exemplify an easily accessible pattern of aqueous synthesis of all-inorganic heterostructured QDs for advanced photosynthetic H 2 evolution.
The installation of heterojunctions on the surfaces of carbon nanotubes (CNTs) is an effective method for promoting the charge separation processes needed for CNT-based electronics and ...optoelectronics applications. Conjugated polymers are proven state-of-the-art candidates for modifying the surfaces of CNTs. However, all previous attempts to incorporate conjugated polymers to CNTs resulted in unordered interfaces. Herein we show that well-defined chains of regioregular poly(3-hexylthiophene) (P3HT) were successfully grown from the surfaces of multiwalled CNTs (MWNTs) using surface-initiated Kumada catalyst-transfer polycondensation. The polymerization was found to proceed in a controlled manner as chains of tunable lengths were prepared through variation of the initial monomer-to-initiator ratio. Moreover, it was determined that large-diameter MWNTs afforded highly ordered P3HT aggregates, which exhibited a markedly bathochromically shifted optical absorption due to a high grafting density induced planarization of the polymer chains. Using ultrafast spectroscopy, the heterojunctions formed between the MWNTs and P3HT were shown to effectively overcome the binding energy of excitons, leading to photoinduced electron transfer from P3HT to MWNTs. Finally, when used as prototype devices, the individual MWNT-g-P3HT core–shell structures exhibited excellent photoresponses under a low illumination density.
The photosynthetic purple bacterium Thermochromatium (Tch.) tepidum is a thermophile that grows at an optimal temperature of ∼50 °C. We have investigated, by means of steady-state and time-resolved ...optical spectroscopies, the effects of temperature on the near-infrared light absorption and the excitation energy transfer (EET) dynamics of its light-harvesting complex 2 (LH2), for which the mesophilic counterpart of Rhodobacter (Rba.) sphaeroides 2.4.1 (∼30 °C) was examined in comparison. In a limited range around the physiological temperature (10–55 °C), the B800-to-B850 EET process of the Tch. tepidum LH2, but not the Rba. sphaeroides LH2, was found to be characteristically temperature-dependent, mainly because of a temperature-tunable spectral overlap. At 55 °C, the LH2 complex from Tch. tepidum maintained efficient near-infrared light harvesting and B800-to-B850 EET dynamics, whereas this EET process was disrupted in the case of Rba. sphaeroides 2.4.1 owing to the structural distortion of the LH2 complex. Our results reveal a remarkable thermal adaptability of the light-harvesting function of Tch. tepidum, which could enhance our understanding of the survival strategy of this thermophile in response to environmental challenges.
Artificial photosystems consisting of semiconductor quantum dots (QDs) and non-noble metal ions (e.g., Fe2+, Co2+, Ni2+) show intrinsic advantages in efficient and cost-effective hydrogen (H2) ...evolution. However, well-controlled integration of these metal ions into ultra-small QDs is a major challenge. Here, we present a two-step strategy to realize site- and spatial-selective integration of earth-abundant Fe2+ ions in CdSe QDs; i.e., CdSe QDs are modified with a thin and anisotropic ZnS shell, and partial Zn2+ ions are selectively substituted by Fe2+ via cation exchange. The anisotropic ZnS layer not only passivates CdSe core but also works as an ideal medium to intimately anchor Fe2+. The multifunctional CdSe/Zn1−xFexS QD exhibits extraordinary activity and stability toward H2 photogeneration. Specifically, more than 880 mL (∼39,300 μmol) H2 gas is produced from 6 mL of aqueous solution during a consecutive 172 h (>1 week) experiment, thus achieving a turnover number of >600,000 per QD.
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•Selective integration of non-noble metal ions in QDs is realized via cation exchange•Multifunctional QDs exhibit extraordinary performance of photocatalytic H2 evolution•Charge transfer is elucidated by steady-state and time-resolved spectroscopies
Artificial photosynthesis is an attractive way to convert sunlight into solar fuels and useful chemicals. Recently, semiconductor quantum dots (QDs) have been verified as promising building blocks to incorporate cocatalysts for effective photocatalysis. However, well-controlled integration of cocatalysts into QDs is quite challenging owing to their ultra-small size and surface complexity. This work reports a two-step strategy for site- and spatial-selective integration of earth-abundant elements into CdSe QDs (∼2.0 nm in diameter) at atomic level via cation exchange. By taking anisotropic ZnS shell as the medium to anchor cocatalysts, the synthetic multifunctional QDs integrate light absorber, protecting layer, and active site together, thus exhibiting remarkable activity and stability toward photocatalytic H2 evolution. This strategy provides a new paradigm for preparing multifunctional ultra-small nanocrystals.
The light absorber, protecting layer, and active site have been integrated into an ultra-small nanocrystal through a site- and spatial-selective cation exchange reaction. Owing to the excellent electronic communication between CdSe and catalytic active sites, the protection of the ZnS shell, and the spatial delocalization of electron-hole pairs, the well-designed multifunctional CdSe/Zn1−xFexS QDs exhibit highly efficient and ultra-stable performance toward photocatalytic H2 evolution.
The excited‐state properties and chain conformations of a new low‐bandgap copolymer based on benzo1,2‐b:4,5‐b′dithiophene (BDT) and thieno3,4‐bthiophene with meta‐alkoxyphenyl‐substituted side chains ...in solution were investigated comprehensively. Time‐resolved spectroscopy suggested that the excited‐state properties were sensitive to the conformations of the copolymer in solution. In addition, excited‐state dynamics analyses revealed the photogeneration of triplet excited states by intersystem crossing (ISC) at a rate constant of ∼0.4×109 s−1 as a result of direct meta‐alkoxyphenyl connection to the donor unit BDT irrespective to the macromolecular conformations. According to El‐Sayed's rule, the fast ISC herein is correlated with the change of orbital types between singlet and triplet excited states as also shown by quantum chemical calculations. Our studies may shed light on the structure–property relationships of photovoltaic materials.
Structure–property relationships: A photovoltaic donor–acceptor copolymer that contains meta‐alkoxyphenyl groups is studied using spectroscopy and quantum chemical calculations to provide information on the charge photogeneration dynamics. The alkoxyphenyl substituent impacts the triplet formation and main chain conformation directly.
A pair of 9-arylidene-9H-fluorene and benzothiadiazole based, low-bandgap copolymers differing merely in the para or meta substitution of alkoxy groups to the arylidene linkages, i.e. p-PAFDTBT and ...m-PAFDTBT respectively, were comparatively investigated by using morphological characterization, ultrafast spectroscopy and quantum chemical calculations. Despite the subtle difference in the alkoxy substitution patterns, p-PAFDTBT molecules in photoactive films were shown to have a higher degree of crystallinity owing to the relatively less rotational torsion of the arylidene linkages. As a result, in either neat or fullerene-blended films, p-PAFDTBT compared to m-PAFDTBT gave rise to a substantially higher charge yield and much slower charge recombination. This work demonstrates that the alkoxy substitution pattern and the arylidene linkage are highly influencing on the morphology of the photoactive layers and thereby on the photovoltaic performance of the semiconducting copolymers.
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