
Justin C JohnsonNational Renewable Energy Laboratory | NREL · Chemical and Materials Science Center
Justin C Johnson
Doctor of Philosophy
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184
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Publications (184)
Combining the synthetic tunability of molecular compounds with the optical selection rules of transition metal dichalcogenides (TMDCs) that derive from spin-valley coupling could provide interesting opportunities for the readout of quantum information. However, little is known about the electronic and spin interactions at such interfaces and the in...
Triplet pairs (TT) in crystalline molecular semiconductors have unique spin properties of interest for quantum information or enhancing solar photoconversion. The population and diffusion dynamics of TT have been the subject of recent studies, both in covalent dimers and in crystalline systems. Here, we monitor the triplet population in neat polycr...
Endothermic singlet fission (SF), an exciton multiplication process that produces a pair of high-energy triplet excitons (T1T1), is appealing for photovoltaic or photoelectrochemical applications, as it allows the conversion of entropy into electronic or chemical energy. The mechanistic aspects of this process are not entirely known, and strategies...
Pentacene is an important model organic semiconductor in both the singlet exciton fission (SF) and organic electronics communities. We have investigated the effect of changing crystal structure on the SF process, generating multiple triplet excitons from an initial singlet exciton, and subsequent triplet recombination. Unlike for similar organic se...
Singlet fission, the process of transforming a singlet excited state into two lower energy triplet excited states, is a promising strategy for improving the efficiency of dye-sensitized solar cells. The difficulty in utilizing singlet fission molecules in this architecture is understanding and controlling the orientation of dyes on mesoporous metal...
The combination of nanostructures with molecular chromophores offers new opportunities to control excited-state photophysics and photochemistry for several potential applications and has fundamental interest for tuning the exciton states that lie at the interface. Semiconductor quantum dots (QDs) are naturally decorated with molecular ligands that...
Innovation in optoelectronic semiconductor devices is driven by a fundamental understanding of how to move charges and/or excitons (electron-hole pairs) in specified directions for doing useful work, e.g. for making fuels or electricity. The diverse and tunable electronic and optical properties of two-dimensional (2D) transition metal dichalcogenid...
Quantum-confined semiconductors provide highly tunable optical and electrical properties for a wide variety of emerging applications. Semiconducting single-walled carbon nanotubes (s-SWCNTs) have shown tremendous potential in applications ranging from digital logic, biological imaging, quantum information processing, photovoltaics, and thermoelectr...
Tetraceno[2,3-b]thiophene is regarded as a strong candidate for singlet fission-based solar cell applications due to its mixed characteristics of tetracene and pentacene that balance exothermicity and triplet energy. An electronically weakly coupled tetraceno[2,3-b]thiophene dimer (Et2Si(TIPSTT)2) with a single silicon atom bridge has been synthesi...
A comprehensive investigation of the solution-phase photophysics of tetracene bis-carboxylic acid [5,12-tetracenepropiolic acid (Tc-DA)] and its related methyl ester [5,12-tetracenepropynoate (Tc-DE)], a non-hydrogen-bonding counterpart, reveals the role of the carboxylic acid moiety in driving molecular aggregation and concomitant excited-state be...
Innovation in optoelectronic semiconductor devices is driven by a fundamental understanding of how to move charges and/or excitons (electron–hole pairs) in specified directions for doing useful work, e.g., for making fuels or electricity. The diverse and tunable electronic and optical properties of two-dimensional (2D) transition metal dichalcogeni...
Conspectus
Preparing and manipulating pure magnetic states in molecular systems are the key initial requirements for harnessing the power of synthetic chemistry to drive practical quantum sensing and computing technologies. One route for achieving the requisite higher spin states in organic systems exploits the phenomenon of singlet fission, which...
Oriented exciton spins that can be generated and manipulated optically are of interest for a range of applications, including spintronics, quantum information science and neuromorphic computing architectures. Although materials that host such excitons often lack practical coherence times for use on their own, strategic transduction of the magnetic...
The multiexciton quintet state, ⁵TT, generated as a singlet fission intermediate in pairs of molecular chromophores, is a promising candidate as a qubit or qudit in future quantum information science schemes. In this work, we synthesize a pyrene-bridged parallel tetracene dimer, TPT, with an optimized interchromophore coupling strength to prevent t...
Controlling the binding of functional organic molecules on quantum dot (QD) surfaces and the resulting ligand/QD interfacial structure determines the resulting organic-inorganic hybrid behavior. In this study, we vary the binding of tetracenedicarboxylate ligands bound to PbS QDs cast in thin films by performing solid-state ligand exchange of as-pr...
Manifesting chemical differences in individual rare earth (RE) element complexes is challenging due to the similar sizes of the tripositive cations and the corelike 4f shell. We disclose a new strategy for differentiating between similarly sized Dy3+ and Y3+ ions through a tailored photochemical reaction of their isostructural complexes in which th...
Singlet fission proceeds through a manifold of triplet-pair states that are exceedingly difficult to distinguish spectroscopically. Here, we introduce a new implementation of photoinduced-absorption-detected magnetic resonance (PADMR) and use it to understand the excited-state absorption spectrum of a tri-2-pentylsilylethynyl pentadithiophene (TSPS...
Manifesting chemical differences in individual rare earth (RE) element complexes is challenging due to the similar sizes of the tripositive cations and the core-like 4f-shell. We disclose a new strategy for differentiating between similarly-sized Dy3+ and Y3+ complexes through a tailored photochemical reaction, where the f-electron states of Dy3+ a...
Photoexcited triplet states are promising candidates for hybrid qubit systems, as they can be used as a controlling gate for nuclear spins. But microwave readout schemes do not generally offer the sensitivity needed to approach the single-molecule limit or the scope to integrate such systems into devices. Here, we demonstrate the possibility of ele...
Materials that are capable of adsorbing and desorbing gases near ambient conditions are highly sought after for many applications in gas storage and separations. While the physisorption of typical gases to high surface area covalent organic frameworks (COFs) occurs through relatively weak intermolecular forces, the tunability of framework materials...
Molecular spin systems based on photoexcited triplet pairs formed via singlet fission (SF) are attractive as carriers of quantum information because of their potentially pure and controllable spin polarization, but developing systems that offer optical routes to readout as well as initialization is challenging. Herein, we characterize the electron...
The photo-driven process of singlet fission generates coupled triplet pairs (TT) with fundamentally intriguing and potentially useful properties. The quintet ⁵ TT 0 sublevel is particularly interesting for quantum information because it is highly entangled, is addressable with microwave pulses, and could be detected using optical techniques. Previo...
Molecular spin systems based on photoexcited triplet pairs formed via singlet fission (SF) are attractive as carriers of quantum information because of their potentially pure and controllable spin polarization, but developing systems that offer optical routes to readout as well as initialization is challenging. Herein, we characterize the electron...
The photo-driven process of singlet fission generates coupled triplet pairs (TT) with fundamentally intriguing and potentially useful properties. The quintet 5TT0 sublevel is particularly interesting for quantum information because it is highly entangled, addressable with microwave pulses, and could be detected using optical techniques. Previous th...
Here we review an emerging class of 2D layered metal-halide perovskites that exhibit important photophysical behavior involving inorganic exciton-To-molecular triplet energy flow. These novel systems have potential to impact several energy-related fields and processes, including optoelectronics, photon upconversion strategies, and triplet-based pho...
β-Mn2V2O7 (β-MVO) was recently reported to be a promising candidate for photoelectrochemical (PEC) water splitting, with a suitable band gap and band edge positions and reasonable stability and photoactivity in preliminary tests in alkaline solution. Here, we present an in-depth evaluation of the PEC performance and stability of phase-pure nanostru...
Photoanodes containing a WO3/BiVO4heterojunction have demonstrated promising photoelectrochemical water splitting performance, but the ability to effectively passivate the WO3/BiVO4interface has limited charge transport and collection. Here, the WO3/BiVO4interface is passivated with a sulfur-modified Bi2O3interfacial layer with a staggered band edg...
Photoinduced electron transfer into mesoporous oxide substrates is well-known to occur efficiently for both singlet and triplet excited states in conventional metal-to-ligand charge transfer (MLCT) dyes. However, in all-organic dyes that have the potential for producing two triplet states from one absorbed photon, called singlet fission dyes, the d...
Ultrafast singlet fission has the potential to facilitate highly efficient photovoltaics through the multiplication of excitons in organic molecular architectures. Here, we consider the interplay of molecular structure and intermolecular coupling toward enabling ultrafast singlet fission and discuss open questions in the field.
Recently, hybrid perovskites have gained attention as sensitizers for molecular triplet generation. Layered, two-dimensional (2D) perovskites are especially well-suited for this purpose because the triplet donor (inorganic framework) and triplet acceptor (organic layer) are self-assembled into adjacent sheets, so that with the appropriate energetic...
The rate of singlet fission, the process of generating two triplet excitons with photoexcitation of one singlet exciton, depends on a combination of singlet/triplet energy balance and intermolecular coupling. Here, we perform carboxylic acid functionalization of anthradithiophene (ADT) derivatives that results in hydrogen bonds that drive molecular...
Simultaneously improving device efficiency and stability is the most important issue in perovskite solar cell (PSC) research. Here, we strategically introduce a multi-functional interface layer (MFIL) with integrated roles of: (1) electron transport, (2) moisture barrier, (3) near-infrared photocurrent enhancement, (4) trap passivation, and (5) ion...
In singlet fission (SF) the initially formed correlated triplet pair state, ¹(TT), may evolve toward independent triplet excitons or higher spin states of the (TT) species. The latter result is often considered undesirable from a light harvesting perspective but may be attractive for quantum information sciences (QIS) applications, as the final exc...
Molecules that undergo singlet fission, converting singlet excitons into pairs of triplet excitons, have potential as photovoltaic materials. The possible advantages of endothermic singlet fission (enhanced use of photon energy and larger triplet energies for coupling with common absorbers) motivated us to assess the role of exciton delocalization...
Colloidal quantum dots (QDs) have emerged as versatile and efficient scaffolds to absorb light and then manipulate, direct, and convert that optical energy into other useful forms of energy. The QD characteristics (optical, electrical, physical) can be readily tuned via solution phase chemistries in order to affect the flow of energy, that was init...
Two pairs of A-D-A molecules have been synthesized with fluorene and benzodithiophene as the central donor subunits and terminal BODIPY units, functionalized with either a 4-methylphenyl or 4-trifluoromethylphenyl group at the meso position. The effect of the para substituent of the meso phenyl group on the photophysical properties of these molecul...
Molecular dimers, oligomers, and polymers are versatile components in photophysical and optoelectronic architectures that could impact a variety of applications. We present a perspective on such systems in the field of singlet fission, which effectively multiplies excitons and produces a unique excited state species, the triplet pair. The choice of...
Copper(II) formate is efficiently incorpated into the pores of a 2D imine-based covalent organic framework (COF) via coordination with the phenol and imine groups. The coordinated metal ion is then reduced to Cu(I) with a thermal treatment that evolves CO2. After loading with hydrogen gas, the majority of H2 desorbs from the coordinatively saturate...
Singlet fission promises to surpass the Shockley–Queisser limit for single-junction solar cell efficiency through the production of two electron–hole pairs per incident photon. However, this promise has not been fulfilled because singlet fission produces two low-energy triplet excitons that have been unexpectedly difficult to dissociate into free c...
We report an investigation of structure and photophysics of thin layers of cibalackrot, a sturdy dye derived from indigo by double annulation at the central double bond. Evaporated layers contain up to three phases, two crystalline and one amorphous. Relative amounts of all three have been determined by a combination of X-ray diffraction and FT-IR...
Diaminoquinones with captodatively stabilized biradicaloid structure are candidates for singlet fission, but few such compounds are known. We report the solution spectroscopy and photophysics of 1,2,2,3-tetramethyl-2,3-dihydro-1H-naphtho[2,3- d ]imidazole-4,9-dione ( 1 ): its steady-state and transient UV-visible absorption, linear dichroism in str...
Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive light-harvesting components for solar photoconversion schemes and architectures, and selective polymer extraction has emerged as a powerful route to obtain highly pure s-SWCNT samples for electronic applications. Here we demonstrate a novel method for producing electronically c...
A process called singlet fission has the potential to enhance the efficiency of solar cells. The mechanism has been difficult to implement in such devices, but experiments demonstrate a way forward. A route towards efficient triplet-exciton transfer into silicon.
The movement of energy and charge at nanoscale interfaces between organics and inorganics could enable novel schemes for photoconversion. We have been exploring ligand exchange and functionalization for nanoscale semiconductors with tunable properties. Lead chalcogenide quantum dots (QDs) have near-infrared band gaps that are ideal for solar harves...
Low-dimensional semiconductors provide a rich tapestry of tunable optical and electrical properties for a wide variety of applications. Semiconducting single-walled carbon nanotubes (s-SWCNTs) have shown tremendous potential in applications ranging from digital logic, biological imaging, quantum information processing, photovoltaics, and thermoelec...
Crystal structures, singlet fission (SF) rate constants, and other photophysical properties are reported for three fluorinated derivatives of 1,3-diphenylisobenzofuran and compared with those of the two crystal forms of the parent. The results place constraints on the notion that the effects of molecular packing on SF rates could be studied separat...
The marriage of colloidal semiconductor nanocrystals and functional organic molecules has brought unique opportunities in emerging photonic and optoelectronic applications. Traditional semiconductor nanocrystals have been widely demonstrated to initiate efficient triplet energy transfer at the nanocrystal-acene interface. Herein, we report that unl...
Singlet fission (SF), the generation of two triplet excitons per the absorption of one photon, is a promising strategy for increasing the efficiencies of solar cells beyond the theoretical Shockley-Queisser limit of 34%. Upon photon absorption by an SF molecule, the initially created singlet excited state (S1) interacts with a neighboring chromopho...
Singlet fission provides a promising route for overcoming the Shockley-Queisser limit in solar cells using organic materials. Despite singlet fission dynamics have been extensively investigated, the transport of the various intermediates in relation to the singlet and triplet states is largely unknown. Here we employ temperature-dependent ultrafast...
We present a cation-exchange approach for tunable A-site alloys of cesium (Cs⁺) and formamidinium (FA⁺) lead triiodide perovskite nanocrystals that enables the formation of compositions spanning the complete range of Cs1–xFAxPbI3, unlike thin-film alloys or the direct synthesis of alloyed perovskite nanocrystals. These materials show bright and fin...
Generating multiple excitons by a single high-energy photon is a promising third generation solar energy conversion strategy. We demonstrate that multiple exciton generation (MEG) in PbS|CdS Janus-like hetero-nanostructures is enhanced over that of single-component and core/shell nanocrystal architectures, with an onset close to two times the PbS b...
Hybrid organic-inorganic halide perovskites have been proposed in many optoelectronic applications, but critical to their increasing functionality and utility is understanding and controlling carrier transport. Here, we use light-induced transient grating spectroscopy to probe directly carrier transport in polycrystalline methylammonium lead iodide...
The hollow cores and well-defined diameters of single-walled carbon nanotubes (SWCNTs) allow for creation of one-dimensional hybrid structures by encapsulation of various molecules. Absorption and near-infrared photoluminescence-excitation (PLE) spectroscopy reveal that the absorption spectrum of encapsulated 1,3-bis[4-(dimethylamino)phenyl]-squara...
A two-dimensional imine-based covalent organic framework (COF) was designed and synthe-sized such that phenyl and perfluorophenyl structural units can seamlessly alternate between layers of the framework. X-ray diffraction of the COF powders reveals a striking increase in crystallinity for the COF with self-complimentary phenyl/perfluorophenyl inte...
Fast-scan cyclic voltammetry permits robust sub-second measurements of in vivo neurotransmitter dynamics, resulting in its established use in elucidating these species’ roles in the actions of behaving animals. However, the technique’s limitations, namely the need for digital background subtraction for analytical signal resolution, have restricted...
The hollow core and well-defined diameters of single-walled carbon nanotubes (SWCNTs) allow for creation of unique one-dimensional hybrid structures by encapsulation of various molecules. For instance, we previously demonstrated that in this way dipolar dye molecules can be naturally aligned in an ideal head-to-tail arrangement to create assemblies...
Semiconducting single-walled carbon nanotubes (s-SWCNTs) are attractive absorbers for use in solar energy harvesting schemes because of their strong and energetically tunable optical absorption, and high charge carrier mobilities due to the delocalized nature of the π-electron system. Beyond their technological potential, s-SWCNTs offer attractive...
We employ a combination of linear spectroscopy, electrochemistry, and transient absorption spectroscopy to characterize the interplay between electron transfer and singlet fission dynamics in polyacene-based dyes attached to nanostructured TiO2. For triisopropyl silylethynyl (TIPS)-pentacene, we find that the singlet fission time constant increases...
We have prepared a series of samples with the ligand 6,13-bistri(iso-propyl)silylethynyl tetracene 2-carboxylic acid (TIPS-Tc-COOH) attached to PbS quantum dot (QD) samples of three different sizes in order to monitor and control the extent and timescales of energy flow after photoexcitation. Fast energy transfer (~1 ps) to the PbS QD occurs upon d...
In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The high...
Due to its ability to offset thermalization losses in photoharvesting systems, singlet fission has become a topic of research interest. During singlet fission, a high energy spin-singlet state in an organic semiconductor divides its energy to form two lower energy spin-triplet excitations on neighboring chromophores. While key insights into mechani...
The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission ra...
A detailed photophysical picture is elaborated for a structurally well-defined and symmetrical bis-tetracene dimer in solution. The molecule was designed for interrogation of initial photophysical steps (S1→1TT) in intramolecular singlet fission (SF). Alkyl-silyl-acetylene substituents on the dimer TIPS-BT1 as well as a monomer model TIPS-Tc enable...
We describe the preparation and excited state dynamics of three alkyl derivatives of 1,3-diphenylisobenzofuran (1) in both solutions and thin films. The substitutions are intended to disrupt the slip-stacked packing observed in crystals of 1 while maintaining the favorable energies of singlet and triplet for singlet fission (SF). All substitutions...
In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The high...
The use of multivariate analysis techniques, such as principal component analysis-inverse least squares (PCA-ILS), has be-come standard for signal isolation from in vivo fast-scan cyclic voltammetric (FSCV) data due to their superior noise re-moval and interferent detection capabilities. However, the requirement of collecting separate training data...
Brain tissue injury is often accompanied by spreading depolarization (SD) events, marked by widespread cellular depolarization and cessation of neuronal firing. SD recruits viable tissue into the lesion, making it a focus for intervention. During SD, drastic fluctuations occur in ion gradients, extracellular neurotransmitter concentrations, cellula...
Due to its high spatiotemporal resolution, fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes enables the localized in vivo monitoring of sub-second fluctuations in electroactive neurotransmitter concentrations. In practice, resolution of the analytical signal relies on digital background subtraction for removal of the large curren...
Tremendous progress and innovation has ushered the incorporation of semiconducting single-walled carbon nanotubes (s-SWCNTs) as active components into organic/inorganic/hybrid solar cells and thermoelectrics. For solar photoconversion, strong and tunable absorption is necessitated, suggesting that s-SWCNTs can play a role as light-harvesting compon...
Fast-scan cyclic voltammetry (FSCV) has been used for over twenty years to study rapid neurotransmission in awake and behaving animals. These experiments were first carried out with carbon-fiber microelectrodes (CFMs) encased in borosilicate glass, which can be inserted into the brain through micromanipulators and guide cannulas. More recently, chr...