No abstract

A semicrystalline p-type thermoelectric conjugated polymer based on a polymer backbone of cyclopentadithiophene and benzothiadiazole, poly­[(4,4′-(bis­(hexyldecyl­sulfanyl)­methylene)­cyclopenta­[2,1-b:3,4-b′]­dithiophene)-alt-(benzo­[c]­[1,2,5]­thiadiazole)] (PCPDTSBT), is designed and synthesized by replacing normal alkyl side-chains with bis­(alkylsulfanyl)­methylene substituents. The sp2-hybridized olefinic bis­(alkylsulfanyl)­methylene side-chains and the sulfur–sulfur (S–S) chalcogen interactions extend a chain planarity with strong interchain packing, which is confirmed by density functional calculations and morphological studies, i.e., grazing incidence X-ray scattering measurement. The doping, electrical, morphological, and thermoelectric characteristics of PCPDTSBT are investigated by comparison with those of poly­[(4,4′-bis­(2-ethylhexyl)­cyclopenta­[2,1-b:3,4-b′]­dithiophene)-alt-(benzo­[c]­[1,2,5]­thiadiazole)] (PCPDTBT) with ethylhexyl side-chains. Upon doping with a Lewis acid, B­(C6F5)3, the maximum electrical conductivity (7.47 S cm–1) of PCPDTSBT is ∼1 order higher than that (0.65 S cm–1) of PCPDTBT, and the best power factor is measured to be 7.73 μW m–1 K–2 for PCPDTSBT with doping 9 mol % of B­(C6F5)3. The Seebeck coefficient–electrical conductivity relation is analyzed by using a charge transport model for polymers, suggesting that the doped PCPDTSBT film has superb charge transport property based on a high crystallinity with olefinic side-chains. This study emphasizes the importance of side-chain engineering by using the sp2-hybridized olefinic substituents to modulate interchain packing, crystalline morphology, and the resulting electrical properties.

Filling the lowest quantum state of the conduction band of colloidal nanocrystals with a single electron, which is analogous to the filling the lowest unoccupied molecular orbital in a molecule with a single electron, has attracted much attention due to the possibility of harnessing the electron spin for potential spin-based applications. The quantized energy levels of the artificial atom, in principle, make it possible for a nanocrystal to be filled with an electron if the Fermi-energy level is optimally tuned during the nanocrystal growth. Here, we report the singly occupied quantum state (SOQS) and doubly occupied quantum state (DOQS) of a colloidal nanocrystal in steady state under ambient conditions. The number of electrons occupying the lowest quantum state can be controlled to be zero, one (unpaired), and two (paired) depending on the nanocrystal growth time via changing the stoichiometry of the nanocrystal. Electron paramagnetic resonance spectroscopy proved the nanocrystals with single electron to show superparamagnetic behavior, which is a direct evidence of the SOQS, whereas the DOQS of the two- or zero-electron occupied nanocrystals in the 1S exhibit diamagnetic behavior. In combination with the superconducting quantum interference device measurement, it turns out that the SOQS of the HgSe colloidal quantum dots has superparamagnetic property. The appearance and change of the steady-state mid-IR intraband absorption spectrum reflect the sequential occupation of the 1S state with electrons. The magnetic property of the colloidal quantum dot, initially determined by the chemical synthesis, can be tuned from diamagnetic to superparamagnetic and vice versa by varying the number of electrons through postchemical treatment. The switchable magnetic property will be very useful for further applications such as colloidal nanocrystal based spintronics, nonvolatile memory, infrared optoelectronics, catalyst, imaging, and quantum computing.

Cancer theragnosis using a single multimodality agent is the next mainstay of modern cancer diagnosis, treatment, and management, but a clinically feasible agent with in vivo cancer targeting and theragnostic efficacy has not yet been developed. A new type of cancer theragnostic agent is reported, based on gold magnetism that is induced on a cancer-targeting protein particle carrier. Superparamagnetic gold-nanoparticle clusters (named SPAuNCs) are synthesized on a viral capsid particle that is engineered to present peptide ligands targeting a tumor cell receptor (TCR). The potent multimodality of the SPAuNCs is observed, which enables TCR-specific targeting, T -weighted magnetic resonance imaging, and magnetic hyperthermia therapy of both subcutaneous and deep-tissue tumors in live mice under an alternating magnetic field. Furthermore, it is analytically elucidated how the magnetism of the SPAuNCs is sufficiently induced between localized and delocalized spins of Au atoms. In particular, the SPAuNCs show excellent biocompatibility without the problem of in vivo accumulation and holds promising potential as a clinically effective agent for cancer theragnosis.

A face-on oriented and p-doped semicrystalline conjugated polymer, poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole)] (PPDT2FBT), was studied as a hole-transport layer (HTL) in methylammonium lead triiodide-based perovskite solar cells (PVSCs). PPDT2FBT exhibits a mid-band gap (1.7 eV), high vertical hole mobility (7.3 × 10 cm/V·s), and well-aligned frontier energy levels with a perovskite layer for efficient charge transfer/transport, showing a maximum power conversion efficiency (PCE) of 16.8%. Upon doping the PPDT2FBT HTL with a nonhygroscopic Lewis acid, tris(pentafluorophenyl)borane (BCF, 2-6 wt %), the vertical conductivity was improved by a factor of approximately 2, and the resulting PCE was further improved up to 17.7%, which is higher than that of standard PVSCs with 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) as an HTL. After BCF doping, the clearly enhanced carrier diffusion coefficient, diffusion length, and lifetime were measured using intensity-modulated photocurrent and photovoltage spectroscopy. Furthermore, compared to the standard PVSCs with spiro-OMeTAD, the temporal device stability was remarkably improved, preserving the ∼60% of the original PCE for 500 h without encapsulation under light-soaking condition (1 sun AM 1.5G) at 85 °C and 85% humidity, which is mainly due to the highly crystalline conjugated backbone of PPDT2FBT and nonhygroscopic nature of BCF. In addition, formamidinium lead iodide/bromide (FAPbIBr)-based PVSCs with the BCF-doped PPDT2FBT as an HTL was also prepared to show 18.8% PCE, suggesting a wide applicability of PPDT2FBT HTL for different types of PVSCs.