Dong Kuk Kim

Carborane-based electron transport material enables high-efficiency, fullerene-free monolithic perovskite/silicon tandem solar cell.

Self-assembled monolayers (SAMs) are a popular choice for achieving high-efficiency perovskite solar cells (PSCs). However, the incomplete wetting of the perovskite on (4-(3,6-dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz) SAMs in PSCs has proven to be a challenge. Recently, the use of surface modifiers such as alumina nanoparticles and poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN–Br) has been demonstrated to eliminate this bottleneck. However, the influence of these surface modifiers on device stability has not been reported. Here, we studied the influence of alumina nanoparticles and PFN–Br on Me-4PACz device stability when stressed under ISOS-D-2I and ISOS-D-2 conditions (at 65 °C). The use of alumina nanoparticles leads to efficient scavenging of iodine, improved bulk electrical and surface electronic homogeneity in fresh films, which is preserved even when the films are degraded, and the formation of 2D perovskites, which act as a barrier against moisture induced degradation. In comparison, perovskites based on PFN–Br show a distinct lack of similar characteristics for fresh and degraded samples. This allows the realisation of alumina modified Me-4PACz based PSCs with a tenfold improved T80 lifetime of 1530 h under ISOS-D-2 conditions compared to the PFN–Br based device stack. Our study uncovers a new approach towards enhancing PSC stability, which could potentially be applied under more strenuous ISOS test conditions to further improve device stability.

Pentacene molecules are deposited onto plasmonic ITO nanocrystals as hybrid organic–inorganic bilayers, holding promise as prospective NIR-modulating electrochromic systems being self-powered by VIS-light-driven photocharging.

As a prototypical organic semiconductor material, pentacene is investigated in numerous electronic and optical systems for its high charge carrier mobility and attractive photophysical properties. However charge generation, transfer and collection remain a critical challenge, especially when considering hybrid structures with inorganic metal oxides as charge acceptors. Herein, pentacene molecular layers are associated with plasmonic electrochromic indium tin oxide (ITO) nanostructures so to allow them to electronically modulate their near-infrared (NIR) absorption in absence of external electric power. Multi-modal surface characterizations show that pentacene molecules transition from a perpendicular orientation when deposited on bare surfaces to more random organization, involving standing-up and face-on orientations, when deposited on ITO. Optoelectronic properties of the interfaced materials are consequently impacted, with steady-state and ultrafast transient spectroscopies further highlighting how electrons are photo-generated in pentacene and consecutively transferred into ITO, ultimately tuning its NIR optical response. Such ITO – pentacene bilayers are therefore holding promise as novel heterojunction-like photoelectrochromic structures, paving the way for the innovative design of self-powered smart windows.

Cs₂AgBiBr₆ double perovskite compounds are increasingly studied in recent years as promising candidates able to counter polluting, harmful, and oxygen‐/moisture‐sensitive issues intrinsic to traditional lead‐containing solar cells. Exhibiting high optical absorption coefficient, low toxicity, and important structural stability, Cs₂AgBiBr₆ solar cells still suffer from limited absorption of low‐energy photons, low carrier mobility, and limited carrier lifetimes induced by defect states. Herein, for the first time, a molecular layer of tetracene is introduced within a Cs₂AgBiBr₆‐based photovoltaic architecture: being incorporated at the interface between the double perovskite photoabsorber and spiro‐OMeTAD hole transport material, tetracene allows for a suitably graded cascade of energy bands within the solar cell architecture, which ultimately improves interfacial charge transfers and reduces charge recombination. The performances in photovoltaic devices are consequently enhanced versus tetracene‐free configurations, with champion values of open‐circuit voltages of 1.1 V (vs. 1.0 V), current densities of 2.5 mA cm⁻² (vs. 1.9 mA cm⁻²), and photoconversion efficiencies of 1.7% (vs. 1.3%) with reduced hysteretic behavior.

This paper reports on the light amplification of NaGdF₄:Yb,Er,Ce@NaGdF₄:Yb,Nd@NaGdF₄ core–shell–shell downconversion nanoparticles (CSS‐DCNPs) in the near‐infrared second biological window (NIR‐II: 1000–1700 nm) by plasmonic nanostructures. Through a precisely controlled plasmonic metallic nanostructure, fluorescence from Yb³⁺ induced 1000 nm emission, Nd³⁺ induced 1060 nm emission, and Er³⁺ induced 1527 nm emission are enhanced 1.6‐fold, 1.7‐fold, and 2.2‐fold, respectively, under an 808 nm laser excitation for the CSS‐DCNPs coupled with a gold hole‐cap nanoarray (Au‐HCNA), while the Er³⁺ induced 1527 nm emission under a 980 nm laser excitation is enhanced up to 6‐fold. To gain insight into the enhancement mechanism, the plasmonic modulation of Er³⁺ induced NIR‐II emission at 1550 nm under 980 nm excitation is studied by FDTD simulation and lifetime measurements, showing the observed fluorescence enhancement can be attributed to a combination of enhanced excitation and an increased radiative decay rate.

Chiral π-conjugated molecules bring new functionality to technological applications and represent an exciting, rapidly expanding area of research. Their functional properties, such as the absorption and emission of circularly polarized light or the transport of spin-polarized electrons, are highly anisotropic. As a result, the orientation of chiral molecules critically determines the functionality and efficiency of chiral devices. Here we present a strategy to control the orientation of a small chiral molecule (2,2′-dicyano[6]helicene) by the use of organic and inorganic templating layers. Such templating layers can either force 2,2′-dicyano[6]helicene to adopt a face-on orientation and self-assemble into upright supramolecular columns oriented with their helical axis perpendicular to the substrate, or an edge-on orientation with parallel-lying supramolecular columns. Through such control, we show that low- and high-energy chiroptical responses can be independently ‘turned on’ or ‘turned off’. The templating methodologies described here provide a simple way to engineer orientational control and, by association, anisotropic functional properties of chiral molecular systems for a range of emerging technologies.

Graphene field-effect transistor (GFET) biosensors exhibit high sensitivity due to a large surface-to-volume ratio and the high sensitivity of the Fermi level to the presence of charged biomolecules near the surface. For most reported GFET biosensors, bulky external reference electrodes are used which prevent their full-scale chip integration and contribute to higher costs per test. In this study, GFET arrays with on-chip integrated liquid electrodes were employed for COVID-19 detection and functionalized with either antibody or aptamer to selectively bind the spike proteins of SARS-CoV-2. In the case of the aptamer-functionalized GFET (aptasensor, Apt-GFET), the limit-of-detection (LOD) achieved was about 10³ particles per mL for virus-like particles (VLPs) in clinical transport medium, outperforming the Ab-GFET biosensor counterpart. In addition, the aptasensor achieved a LOD of 160 aM for COVID-19 neutralizing antibodies in serum. The sensors were found to be highly selective, fast (sample-to-result within minutes), and stable (low device-to-device signal variation; relative standard deviations below 0.5%). A home-built portable readout electronic unit was employed for simultaneous real-time measurements of 12 GFETs per chip. Our successful demonstration of a portable GFET biosensing platform has high potential for infectious disease detection and other health-care applications.

In the search for high performance n-type organic semiconductors (OSCs) a simple strategy might be substitution of aromatic CH groups for nitrogen heteroatoms. Here, we report the synthesis and characterisation of two novel N-heteroacene compounds, namely, 1,5,12-triazatetracene (TrAT1) and 2,5,12-triazatetracene (TrAT2). Their potential as n-type materials is evaluated against 5,12-diazatetracene (DAT) by UV/vis and EPR spectroscopy, cyclic voltammetry, DFT, single crystal X-ray diffraction and thin film characterisation. Increasing the number of N-heteroatoms was found to stabilise the HOMO and LUMO leading to electron affinities for TrAT1 and TrAT2 of ca. −4 eV. Both compounds were found to exhibit columns of co-facial π-stacked molecules. For TrAT1, molecules are also linked by hydrogen bonding, while the crystal structure of TrAT2 was found to be inherently disordered. Thin films of DAT, TrAT1 and TrAT2 were grown by organic molecular beam deposition (OMBD) and found to form discontinuous films, where TrAT1 exhibited a preferential orientation.