Anthony S. R. Chesman

Cu2ZnSnS4xSe4(1–x) Solar Cells from Polar Nanocrystal Inks

A facile ligand exchange method for dispersing Cu2ZnSnS4 (CZTS) nanocrystals (NCs) in environmentally benign polar solvents, such as ethanol or n-propanol, at high concentrations (up to 200 mg/mL) is demonstrated. This approach has been applied to CZTS nanocrystals synthesized via scalable, noninjection methods to formulate colloidally stable inks that are suitable for the solution processing of solar cell devices. Unlike other inks currently used to fabricate NC solar cells, the CZTS nanocrystal ink developed here circumvents the need for hydrazine, pyridine, or thiol coordinating solvents. By combining our polar CZTS inks with optimized selenization procedures, substrate CZTSSe solar cells have been successfully fabricated with device efficiencies of 7.7%.

An Alkylated Indacenodithieno[3,2‐b]thiophene‐Based Nonfullerene Acceptor with High Crystallinity Exhibiting Single Junction Solar Cell Efficiencies Greater than 13% with Low Voltage Losses

A new synthetic route, to prepare an alkylated indacenodithieno[3,2-b]thiophene-based nonfullerene acceptor (C8-ITIC), is reported. Compared to the reported ITIC with phenylalkyl side chains, the new acceptor C8-ITIC exhibits a reduction in the optical band gap, higher absorptivity, and an increased propensity to crystallize. Accordingly, blends with the donor polymer PBDB-T exhibit a power conversion efficiency (PCE) up to 12.4%. Further improvements in efficiency are found upon backbone fluorination of the donor polymer to afford the novel material PFBDB-T. The resulting blend with C8-ITIC shows an impressive PCE up to 13.2% as a result of the higher open-circuit voltage. Electroluminescence studies demonstrate that backbone fluorination reduces the energy loss of the blends, with PFBDB-T/C8-ITIC-based cells exhibiting a small energy loss of 0.6 eV combined with a high JSC of 19.6 mA cm-2 .

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

Non-injection Synthesis of Doped Zinc Oxide Plasmonic Nanocrystals

Plasmonic metal oxide nanocrystals bridge the optoelectronic gap between semiconductors and metals. In this study, we report a facile, non-injection synthesis of ZnO nanocrystals doped with Al, Ga, or In. The reaction readily permits dopant/zinc atomic ratios of over 15%, is amenable to high precursor concentrations (0.2 M and greater), and provides high reaction yields (>90%). The resulting colloidal dispersions exhibit high transparency in the visible spectrum and a wavelength-tunable infrared absorption, which arises from a dopant-induced surface plasmon resonance. Through a detailed investigation of reaction parameters, the reaction mechanism is fully characterized and correlated to the optical properties of the synthesized nanocrystals. The distinctive optical features of these doped nanocrystals are shown to be readily harnessed within thin films that are suitable for optoelectronic applications.

The chemistry and complexes of small cyano anions

The chemistry of the anions dicyanamide and tricyanomethanide (dca and tcm, respectively) has produced a plethora of discoveries over the past few decades, particularly in relation to transition-metal coordination polymers with magnetic coupling. Over recent years there have been an increasing number of reports of heterofunctionalised cyano-containing anions, typically derivatives of dicyanomethanide. Our own group has been particularly concerned with the amide- and nitroso-functionalised anions carbamoyldicyanomethanide (cdm) and dicyanonitrosomethanide (dcnm), respectively. This feature article examines the fascinating diversity of materials and complexes that can be obtained using small cyano anions, ranging from coordination polymers to heterometallic clusters and hydrogen bonding networks. In particular, we focus on results from our own laboratories in the past few years. The magnetic properties of these materials are briefly discussed.

Homoleptic 12-coordinate lanthanoids with η2-nitroso ligands

The complexes [Et4N]3[Ln(η2-dcnm)6] (Ln = La, Ce, Nd, Gd, dcnm = dicyanonitrosomethanide) have discrete N, O 12-coordination owing to symmetrical chelation of the nitroso donor groups.

Stabilizing the cubic perovskite phase of CsPbI3 nanocrystals by using an alkyl phosphinic acid

CsPbI3 nanocrystals suffer from a facile cubic perovskite to orthorhombic phase transformation, which deteriorates their appealing optoelectronic properties. Here, we report a new colloidal synthesis that replaces the conventionally used oleic acid with an alkyl phosphinic acid to grow high-quality, phase-stable cubic perovskite CsPbI3 nanocrystals.

In situ ligand formation in the synthesis of an octanuclear dysprosium ‘double cubane’ cluster displaying single molecule magnet features

The nucleophilic addition of methanol and water to the dicyanonitrosomethanide anion, resulting in the formation of cyano(imino(methoxy)methyl)nitrosomethanide (cmnm) and carbamoylcyanonitrosomethanide (ccnm), respectively, is used as a means of in situ ligand synthesis during the formation of [Dy(8)(OH)(6)(OMe)(6)(cmnm)(10)(ccnm)(2)(H(2)O)(2)(MeOH)(2)] (1). This is the first time these reactions have been observed to be promoted by the presence of a lanthanoid ion. The core of the octanuclear cluster consists of two cubane moieties ([Dy(4)(OH)(3)(OMe)]), bridged by four methoxide ligands to form a central [Dy(8)(OH)(6)(OMe)(6)] moiety. The complex displays magnetic properties that are indicative of probable single molecule magnet features.

Lanthanoid‐Based Ionic Liquids Incorporating the Dicyanonitrosomethanide Anion

A series of low-melting-point salts with hexakisdicyanonitrosomethanidolanthanoidate anions has been synthesised and characterised: (C(2) mim)(3) [Ln(dcnm)(6)] (1 Ln; 1 Ln=1 La, 1 Ce, 1 Pr, 1 Nd), (C(2) C(1) mim)(3) [Pr(dcnm)(6)] (2 Pr), (C(4) C(1) pyr)(3) [Ce(dcnm)(6)] (3 Ce), (N(1114))(3) [Ln(dcnm)(6)] (4 Ln; 4 Ln=4 La, 4 Ce, 4 Pr, 4 Nd, 4 Sm, 4 Gd), and (N(1112OH) )(3) [Ce(dcnm)(6)] (5 Ce) (C(2) mim=1-ethyl-3-methylimidazolium, C(2) C(1) mim=1-ethyl-2,3-dimethylimidazolium, C(4) C(1) py=N-butyl-4-methylpyridinium, N(1114) =butyltrimethylammonium, N(1112OH) =2-(hydroxyethyl)trimethylammonium=choline). X-ray crystallography was used to determine the structures of complexes 1 La, 2 Pr, and 5 Ce, all of which contain [Ln(dcnm)(6)](3-) ions. Complexes 1 Ln and 2 Pr were all ionic liquids (ILs), with complex 3 Ce melting at 38.1 °C, the lowest melting point of any known complex containing the [Ln(dcnm)(6)](3-) trianion. The ammonium-based cations proved to be less suitable for forming ILs, with complexes 4 Sm and 4 Gd being the only salts with the N(1114) cation to have melting points below 100 °C. The choline-containing complex 5 Ce did not melt up to 160 °C, with the increase in melting point possibly being due to extensive hydrogen bonding, which could be inferred from the crystal structure of the complex.

Theoretical and experimental insights into the mechanism of the nucleophilic addition of water and methanol to dicyanonitrosomethanide.

In this work the nucleophilic addition of water and methanol to the dicyanonitrosomethanide anion (dcnm, [C(CN)(2)(NO)](-)) in the absence of the usual transition metal promoters was investigated. Experimentally it was shown that a quantitative conversion of the dcnm anion to carbamoylcyanonitrosomethanide (ccnm, [C(CN)(CONH(2))(NO)](-)) by the addition of 1 equiv of water to a nitrile group is complete in 48 h at 100 °C, or in 1.5 h at 150 °C when the reaction is conducted in a microwave reactor. Attempts to add a second equivalent of water to the anion failed with thermal degradation of the anion occurring at 200 °C. Ab initio calculations show that the reaction proceeds via three distinct transition states: (1) the transfer of a proton from a water molecule to the nitrile group, (2) the subsequent attack of the generated hydroxide anion on the carbon atom of the nitrile group, and (3) a rapid proton transfer to form a carbamoyl group. The attacking water molecule is shown to be a stronger proton donor when modeled as part of a hydrogen-bonded three water molecule chain, leading to a significant reduction in the reaction barrier. Only the anti-ccnm anion is formed in the reaction. There is a high-energy barrier to the formation of the syn isomer by the rotation of the nitroso group. While the syn isomer of ccnm is shown to be the more thermodynamically stable conformation, examination of the HOMO-1 molecular orbital that arises during the second transition state of the reaction indicates the addition of the hydroxide anion to the carbon atom is forbidden due to orbital symmetry, with a similar effect responsible for the failure of a second equivalent of water to add to the ccnm anion. Under analogous reaction conditions the addition of 1 equiv of methanol to dcnm to form cyano(imino(methoxy)methyl)nitrosomethanide (cmnm, [C(CN)(C(OMe)NH)(NO)](-)) failed, although ab initio calculations initially indicated the reaction should proceed more readily than the addition of water. When the energy required to break the hydrogen-bonded cyclic hexamers in methanol is taken into consideration, the energy barrier to the first transition step is greatly increased. The addition of a second equivalent of methanol to cmnm is unlikely to occur even in the presence of a transition metal as the resultant anion would be marginally thermodynamically unstable.