The morphology of bulk heterojunction organic photovoltaic cells controls many of the performance characteristics of devices. However, measuring this morphology is challenging because of the small ...length-scales and low contrast between organic materials. Here we use nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high-performance blend of PTB7:PC71BM. We show that optimized blends consist of elongated fullerene-rich and polymer-rich fibre-like domains, which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion that helps in the extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene domains show a much lower efficiency of charge extraction of ~45%, which is attributed to poor electron and hole transport. Our results show that the formation of narrow and elongated domains is desirable for efficient bulk heterojunction solar cells.
The structural order of biopolymers, such as proteins, at interfaces defines the physical and chemical interactions of biological systems with their surroundings and is hence a critical parameter in ...a range of biological problems. Known spectroscopic methods for routine rapid monitoring of structural order in biolayers are generally only applied to model single-component systems that possess a spectral fingerprint which is highly sensitive to orientation. This spectroscopic behavior is not a generic property and may require the addition of a label. Importantly, such techniques cannot readily be applied to real multicomponent biolayers, have ill-defined or unknown compositions, and have complex spectroscopic signatures with many overlapping bands. Here, we demonstrate the sensitivity of plasmonic fields with enhanced chirality, a property referred to as superchirality, to global orientational order within both simple model and “real” complex protein layers. The sensitivity to structural order is derived from the capability of superchiral fields to detect the anisotropic nature of electric dipole–magnetic dipole response of the layer; this is validated by numerical simulations. As a model study, the evolution of orientational order with increasing surface density in layers of the antibody immunoglobulin G was monitored. As an exemplar of greater complexity, superchiral fields are demonstrated, without knowledge of exact composition, to be able to monitor how qualitative changes in composition alter the structural order of protein layers formed from blood serum, thereby establishing the efficacy of the phenomenon as a tool for studying complex biological interfaces.
The effect of acceptor energy level on electron transfer rate in blends of the polymer solar‐cell material ...poly4,8‐bis(2‐ethylhexyl)oxybenzo1,2‐b:4,5‐b′dithiophene‐2,6‐diyl3‐fluoro‐2‐(2‐ethylhexyl)carbonylthieno3,4‐bthiophenediyl (PTB7) is studied using time‐resolved fluorescence. Fast electron transfer in less than 2 ps is observed for a driving force between 0.2 and 0.6 eV and the electron transfer is slower outside this range. This dependence is described by Marcus theory with a reorganization energy of ≈0.4 eV.
We report the fabrication of solution-processed bulk heterojunction devices from subphthalocyanine (SubPc) units as the acceptor component and conventional polymeric donor materials such as MEH-PPV, ...P3HT and PTB7. The high solubility of the SubPc derivatives facilitated the formation of efficient donor/acceptor networks and provided power conversion efficiencies of 0.4% with MEH-PPV, 1.1% with P3HT and 3.5% with PTB7. A clear contribution of photon harvesting by the acceptor was identified from the external quantum efficiency spectra. Analysis of the current–voltage characteristics and photoluminescence quenching revealed trap-assisted and geminate recombination as a loss mechanism. Our results show that solution-processable SubPcs are a promising alternative to fullerenes for polymer solar cells.
In this article, we report the formation of micelles from a tetrathiafulvalene (TTF) end-functionalized poly(N-isopropylacrylamide) (poly(NIPAM)) derivative (1). We have determined the critical ...aggregation concentration (CAC) and average diameter of the micelles using fluorescence spectroscopy and dynamic light scattering experiments, respectively. We have exploited the NIPAM backbone of the polymer to thermally transform the swollen hydrophilic poly(NIPAM) derivative to a more globular hydrophobic state at the lower critical solution temperature (LCST). Finally, we have shown that we can exploit the chemical oxidation and complexation properties of the TTF unit to disrupt the micelle architecture to release the hydrophobic dye Nile Red from the interior of the micelle.
Optimal performance of nanophotonic devices, including sensors and solar cells, requires maximizing the interaction between light and matter. This efficiency is optimized when active moieties are ...localized in areas where electromagnetic (EM) fields are confined. Confinement of matter in these 'hotspots' has previously been accomplished through inefficient 'top-down' methods. Here we report a rapid 'bottom-up' approach to functionalize selective regions of plasmonic nanostructures that uses nano-localized heating of the surrounding water induced by pulsed laser irradiation. This localized heating is exploited in a chemical protection/deprotection strategy to allow selective regions of a nanostructure to be chemically modified. As an exemplar, we use the strategy to enhance the biosensing capabilities of a chiral plasmonic substrate. This novel spatially selective functionalization strategy provides new opportunities for efficient high-throughput control of chemistry on the nanoscale over macroscopic areas for device fabrication.
Organic hole-transporting materials (HTM) have shown excellent ability in achieving high efficiency perovskite solar cells. However, their high cost significantly limits their applications in ...scaling-up perovskite solar cells. Here, we report an efficient, low-cost HTM, called TAT- t BuSty, comprising a central triazatruxene moiety with 3 terminal tert -butoxy styrene groups and 3 hexyl side chains on the indole nitrogen. For the first time, we use an inexpensive liquid precursor to attach the donor ligand to the molecule. This enables purification of the HTM using a silica plug and recrystallization without the need for complicated column chromatography, which is typically required to purify solid-precursor-prepared HTMs. We estimate that the cost for the purified TAT- t BuSty is $69.90 g −1 , which is 35% cheaper than the widely-used 2,2′7,7′-tetrakis-( N,N -di- p -methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD; ca. $112.05 g −1 ). Using this low-cost TAT- t BuSty as the HTM in a caesium-formamidinium mixed-cation perovskite solar cell, we have successfully achieved a champion power conversion efficiency (PCE) of 20.3% (19.4% stabilized efficiency), which is comparable to the efficiency of devices using the reference spiro-OMeTAD HTM. Our work is crucial for up-scaling of next-generation high-performance metal-halide perovskite solar cells.
The application of electrochemistry or photochemistry to modulate supramolecular interactions between host–guest systems in solution is a burgeoning field. In particular, the speed and reversibility ...associated with electrochemically or photochemically actuated supramolecular interactions has allowed the creation and modulation of novel solution‐based devices. In recent years, great advances have been made in transferring these systems from the solution to the solid state, to facilitate the development of molecular‐electronics components that can operate in unison under the influence of an externally applied stimulus. These studies pave the way for the creation of responsive surfaces with advanced materials and nanotechnology applications.
Solid progress: The transfer of responsive supramolecular systems from the solution to the solid state by immobilizing their components onto surfaces is an attractive method for developing systems with molecular electronics and device applications (see scheme). The ability to coherently interface these systems with the outside world may pave the way for their implementation as novel components within the emerging advanced materials and nanotechnology industries.
Hydrogen bonding heavily influences conformations, rate of reactions, and chemical equilibria. The development of a method to monitor hydrogen bonding interactions independent of polarity is ...challenging as both are linked. We have developed two solvatochromic dyes that detect hydrogen-bond-donating solvents. The unique solvatochromism of the triazine architecture has allowed the development of probes that monitor hydrogen-bond-donating species including water.
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