Capacitive and Efficient Near-Infrared Stimulation of Neurons via an Ultrathin AgBiS2 Nanocrystal Layer.

Colloidal nanocrystals (NCs) exhibit significant potential for photovoltaic bioelectronic interfaces because of their solution processability, tunable energy levels, and inorganic nature, lending them chemical stability. Silver bismuth sulfide (AgBiS2) NCs, free from toxic heavy-metal elements (e.g., Cd, Hg, and Pb), particularly offer an exceptional absorption coefficient exceeding 105 cm-1 in the near-infrared (NIR), surpassing many of their inorganic counterparts. Here, we integrated an ultrathin (24 nm) AgBiS2 NC layer into a water-stable photovoltaic bioelectronic device architecture that showed a high capacitive photocurrent of 2.3 mA·cm-2 in artificial cerebrospinal fluid (aCSF) and ionic charges over 10 µC·cm-2 at a low NIR intensity of 0.5 mW·mm-2. The device without encapsulation showed a halftime of 12.5 years under passive accelerated aging test and did not show any toxicity on neurons. Furthermore, patch-clamp electrophysiology on primary hippocampal neurons under whole-cell configuration revealed that the device elicited neuron firing at intensity levels more than an order of magnitude below the established ocular safety limits. These findings point to the potential of AgBiS2 NCs for photovoltaic retinal prostheses.

A Universal Perovskite Nanocrystal Ink for High-Performance Optoelectronic Devices.

Semiconducting lead halide perovskite nanocrystals (PNCs) are regarded as promising candidates for next-generation optoelectronic devices due to their solution processability and outstanding optoelectronic properties. While the field of light-emitting diodes (LEDs) and photovoltaics (PVs), two prime examples of optoelectronic devices, has recently seen a multitude of efforts toward high-performance PNC-based devices, realizing both devices with high efficiencies and stabilities through a single PNC processing strategy has remained a challenge.  In this work, diphenylpropylammonium (DPAI) surface ligands, found through a judicious ab-initio-based ligand search, are shown to provide a solution to this problem. The universal PNC ink with DPAI ligands presented here, prepared through a solution-phase ligand-exchange process, simultaneously allows single-step processed LED and PV devices with peak electroluminescence external quantum efficiency of 17.00% and power conversion efficiency of 14.92% (stabilized output 14.00%), respectively. It is revealed that a careful design of the aromatic rings such as in DPAI is the decisive factor in bestowing such high performances, ease of solution processing, and improved phase stability up to 120 days. This work illustrates the power of ligand design in producing PNC ink formulations for high-throughput production of optoelectronic devices; it also paves a path for "dual-mode" devices with both PV and LED functionalities.

Guanidinium-Pseudohalide Perovskite Interfaces Enable Surface Reconstruction of Colloidal Quantum Dots for Efficient and Stable Photovoltaics.

Complete surface passivation of colloidal quantum dots (CQDs) and their strong electronic coupling are key factors toward high-performance CQD-based photovoltaics (CQDPVs). Also, the CQD matrices must be protected from oxidative environments, such as ambient air and moisture, to guarantee air-stable operation of the CQDPVs. Herein, we devise a complementary and effective approach to reconstruct the oxidized CQD surface using guanidinium and pseudohalide. Unlike conventional halides, thiocyanate anions provide better surface passivation with effective replacement of surface oxygen species and additional filling of defective sites, whereas guanidinium cations promote the construction of epitaxial perovskite bridges within the CQD matrix and augment electronic coupling. Additionally, we replace a defective 1,2-ethanedithiol-treated CQD hole transport layer (HTL) with robust polymeric HTLs, based on a judicious consideration of the energy level alignment established at the CQD/HTL interface. These efforts collectively result in high-performance and stable CQDPVs with photocurrents over 30 mA cm-2, ∼80% quantum efficiency at excitonic peaks and stable operation under humid and ambient conditions. Elucidation of carrier dynamics further reveals that interfacial recombination associated with band alignment governs both the CQDPV performance and stability.

Effect of electron-withdrawing fluorine and cyano substituents on photovoltaic properties of two-dimensional quinoxaline-based polymers.

In this study, strong electron-withdrawing fluorine (F) and cyano (CN) substituents are selectively incorporated into the quinoxaline unit of two-dimensional (2D) D-A-type polymers to investigate their effects on the photovoltaic properties of the polymers. To construct the 2D polymeric structure, electron-donating benzodithiophene and methoxy-substituted triphenylamine are directly linked to the horizontal and vertical directions of the quinoxaline acceptor, respectively. After analyzing the structural, optical, and electrochemical properties of the resultant F- and CN-substituted polymers, labeled as PBCl-MTQF and PBCl-MTQCN, respectively, inverted-type polymer solar cells with a non-fullerene Y6 acceptor are fabricated to investigate the photovoltaic performances of the polymers. It is discovered that the maximum power conversion efficiency of PBCl-MTQF is 7.48%, whereas that of PBCl-MTQCN is limited to 3.52%. This significantly reduced PCE of the device based on PBCl-MTQCN is ascribed to the formation of irregular, large aggregates in the active layer, which can readily aggravate the charge recombination and charge transport kinetics of the device. Therefore, the photovoltaic performance of 2D quinoxaline-based D-A-type polymers is significantly affected by the type of electron-withdrawing substituent.

Solvent Engineering of Colloidal Quantum Dot Inks for Scalable Fabrication of Photovoltaics.

Development of colloidal quantum dot (CQD) inks enables single-step spin-coating of compact CQD films of appropriate thickness, enabling the promising performance of CQD photovoltaics (CQDPVs). Today's highest-performing CQD inks rely on volatile n-butylamine (BTA), but it is incompatible with scalable deposition methods since a rapid solvent evaporation results in irregular film thickness with an uneven surface. Here, we present a hybrid solvent system, consisting of BTA and N,N-dimethylformamide, which has a favorable acidity for colloidal stability as well as an appropriate vapor pressure, enabling a stable CQD ink that can be used to fabricate homogeneous, large-area CQD films via spray-coating. CQDPVs fabricated with the CQD ink exhibit suppressed charge recombination as well as fast charge extraction compared with conventional CQD ink-based PVs, achieving an improved power conversion efficiency (PCE) of 12.22% in spin-coated devices and the highest ever reported PCE of 8.84% among spray-coated CQDPVs.

Hybrid Surface Passivation for Retrieving Charge Collection Efficiency of Colloidal Quantum Dot Photovoltaics.

Efficient charge collection in photovoltaics is a key issue toward their high performance. Despite the promising performance of colloidal quantum dot (CQD)-based photovoltaics (CQDPVs), they suffer significant dissipation of photocurrent due to imperfect surface passivation of the CQD hole transport layer (HTL) by a single 1,2-ethaneditihol (EDT) ligand. To address the critical drawback of existing CQDPVs, we offer a hybrid passivation strategy, including both EDT and thiocyanate (SCN). The hybrid passivation leads to seamless surface passivation of CQDs, remarkably suppressing charge recombination. This strategy also augments the p-doping density of the CQD, resulting in a pronounced energy level bending at the active layer/HTL interface and facilitating efficient charge separation. Moreover, enhanced electronic coupling across the CQDs (originating from reduced inter-dot spacing) promotes rapid charge extraction. Consequently, the flawless charge collection by a hybrid-passivated HTL successfully retrieves the photocurrent, achieving an enhanced CQDPV power conversion efficiency of 12.70% compared with 11.49% for the control device.

Water-resistant AgBiS2 colloidal nanocrystal solids for eco-friendly thin film photovoltaics.

Lead-free, water-resistant photovoltaic absorbers are of significant interest for use in environment-friendly and water-stable thin film solar cells. However, there are no reports on the water-resistance characteristics of such photoactive materials. Here, we demonstrate that silver bismuth sulfide (AgBiS2) nanocrystal solids exhibit inherent water resistance and can be employed as effective photovoltaic absorbers in all-solid-state thin film solar cells that show outstanding air and moisture stabilities under ambient conditions. The results of X-ray photon spectroscopy (XPS) and X-ray diffraction (XRD) analyses show that there is no change in the chemical composition and crystal structure of the AgBiS2 nanocrystal solids after a water treatment. Based on these results, AgBiS2 nanocrystal solar cells are fabricated. These devices also do not show any drop in performance after a water treatment, confirming that the AgBiS2 nanocrystal solids are indeed highly water-resistant. In contrast, lead sulfide (PbS) colloidal quantum dot (CQD) solar cells show significant decrease in performance after a similar water treatment. Using XPS analysis and density functional theory (DFT) calculations, we confirm that the iodine removal and the surface hydroxylation of the water-treated PbS CQD solids are the primary reasons for the observed decrease in the device performance of the CQD solar cells.

Solution-Processed "Silver-Bismuth-Iodine" Ternary Thin Films for Lead-Free Photovoltaic Absorbers.

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. However, poor surface morphologies and relatively high bandgap energies have limited their potential. Silver-bismuth-iodine (Ag-Bi-I) is a promising semiconductor for optoelectronic devices. Therefore, we demonstrate the fabrication of Ag-Bi-I ternary thin films using material solution processing. The resulting thin films exhibit controlled surface morphologies and optical bandgaps according to their thermal annealing temperatures. In addition, it has been reported that Ag-Bi-I ternary systems crystallize to AgBi2I7, Ag2BiI5, etc. according to the ratio of the precursor chemicals. The solution-processed AgBi2I7 thin films exhibit a cubic-phase crystal structure, dense, pinhole-free surface morphologies with grains ranging in size from 200 to 800 nm, and an indirect bandgap of 1.87 eV. The resultant AgBi2I7 thin films show good air stability and energy band diagrams, as well as surface morphologies and optical bandgaps suitable for lead-free and air-stable single-junction solar cells. Very recently, a solar cell with 4.3% power conversion efficiency was obtained by optimizing the Ag-Bi-I crystal compositions and solar cell device architectures.

Water-resistant PEDOT:PSS hole transport layers by incorporating a photo-crosslinking agent for high-performance perovskite and polymer solar cells.

We demonstrated a water-resistant PEDOT:PSS HTL by incorporating a photo-crosslinking agent into a PEDOT:PSS film. A crosslinking system was successfully formed inside the PEDOT:PSS film by simple and fast photo-polymerization of PCDSA monomers. Combination of the crosslinking system and MeOH surface treatment simultaneously improved the device efficiency and stability of both perovskite and polymer solar cells. The crosslinking system inside PEDOT:PSS changed its intrinsic water-soluble characteristic into a water-resistant property, thus preventing water penetration into the PEDOT:PSS film. In addition, MeOH treatment improved the surface conductivity and reduced the surface roughness of the PEDOT:PSS film by removing surface residues of PDAs and insulating PSS parts.

Twisted Linker Effect on Naphthalene Diimide-Based Dimer Electron Acceptors for Non-fullerene Organic Solar Cells.

Naphthalene diimide (NDI) dimers, NDI-Ph-NDI with a phenyl linker and NDI-Xy-NDI with a xylene linker, are designed and synthesized. The influence of the xylene and phenyl linkers on optical properties, electrochemical properties, morphology, and device performance is systematically investigated. Non-fullerene organic solar cells (OSCs) with NDI-Ph-NDI show poor device efficiency due to aggregation of polymer chains and/or NDI dimers caused by the highly planar structure of NDI-Ph-NDI. Although NDI-Xy-NDI is a non-planar structure, uniform surface morphology and weak bimolecular recombination lead to high power conversion efficiencies of 3.11%, which is the highest value in non-fullerene OSCs with NDI small molecules.

Proteomic analysis of phosphotyrosyl proteins in morphine-dependent rat brains.

Morphine has been used as a potent analgesic, having a high propensity to induce tolerance and physical dependence following their repeated administration. Although the mechanisms that underlie the development of dependence on morphine remain unclear, previous studies suggested that phosphorylations of diverse types of cellular proteins are crucial determinants of the neuroadaptive mechanisms associated with morphine dependence. Thus, understanding global phosphorylation events induced by chronic morphine administration is essential for understanding the complex signaling mechanisms of morphine dependence. This study characterized the alteration of tyrosine phosphorylation of frontal cortical proteins in morphine-dependent rat brains using a proteomic approach. Dependence was produced by continuous intracerebroventricular (i.c.v.) infusion of morphine (26 nmol/microl/h) for 72 h via osmotic minipumps in rats. Phosphotyrosyl (p-Tyr) protein spots in brain frontal cortical regions were detected by two-dimensional electrophoresis (2-DE) and immunoblotting with anti-p-Tyr-specific antibodies. The protein spots showing significant changes in tyrosine phosphorylation were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Similar patterns of protein expression were detected by 2-DE gels in morphine-dependent and saline-treated control rat brains. However, phosphotyrosine 2-DE images of the frontal cortical proteins from saline-treated control and morphine-dependent rat brains were apparently different. The densities of most matched p-Tyr protein spots were increased in morphine-dependent rat brains compared with that of control samples. Additional p-Tyr protein spots were detected in 2-DE image of morphine-dependent rat brains. Fifty of p-Tyr protein spots, corresponding to 40 different proteins, were identified from 2-DE gels of morphine-dependent rat brains. The identified proteins include enzymes, cytoskeletal proteins, cell signaling molecules, and other proteins. In conclusion, the first available phosphotyrosine proteomic resources of morphine dependence were established using an animal model. The findings illustrate the potential of proteomics as an effective technique for studying phosphorylation events of morphine dependence in brains.

Proteomic analysis of phosphotyrosyl proteins in the rat brain: effect of butorphanol dependence.

Butorphanol (17-cyclobutylmethyl-3,14-dihydroxymorphinan) tartrate (Stadol) is a mixed agonist-antagonist opioid analgesic agent that is about five to seven times as potent as morphine in analgesic effects. The chronic use of butorphanol produces physical dependence in humans and animals. Phosphorylation plays a very important role in developing butorphanol dependence; however, global phosphorylation events induced by chronic butorphanol administration have not been reported. The aim of this study is to determine the alteration of tyrosine phosphorylation of brain frontal cortical proteins in butorphanol-dependent rats using a proteomic approach. Dependence was produced by continuous intracerebroventricular (i.c.v.) infusion of butorphanol (26 nmol/microl/hr) for 72 hr via osmotic minipump in rats. Similar patterns of protein expression were detected by two-dimensional electrophoresis (2-DE) in brain frontal cortex of butorphanol-dependent and saline-treated control rats. All 65 phosphotyrosyl (p-Tyr) protein spots detected in pH 3-10 phosphotyrosine 2-DE of control rat brains were detected in butorphanol-dependent rat brains. The densities of most p-Tyr protein spots were increased in butorphanol-dependent rat brains compared to saline-treated control samples. Eighteen additional p-Tyr protein spots were detected in pH 3-10 2-DE images of butorphanol-dependent rat brains. Immobilized pH strips with three different narrow pH ranges were examined to improve the resolution of p-Tyr proteins in 2-DE gels. Fifty-three p-Tyr protein spots were identified as known proteins involved in cell cytoskeleton, cell metabolism, and cell signaling. This proteomic approach can provide useful information for understanding the complex mechanism of butorphanol dependence in vivo.