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International audience; A metal–insulator–semiconductor (MIS) structure based on an inhomogeneous junction has been recently proven to be highly efficient at photoelectrochemical (PEC) water oxidation. Engineering the surrounding layer of the MIS nanojunction is crucial to maximizing the photovoltage. Specifically, for an n-type photoanode, a high work-function material is required to create a large Schottky barrier that assists the hole transfer to oxidize water while blocking the electron transfer. Normally, the surrounding layer is a native oxidized phase of the metal layer that forms unintentionally. Herein, we demonstrate the use of copper(I) thiocyanate (CuSCN), a transparent p-type coordination polymer semiconductor with a high work function, to specifically surround the n-Si/SiOx/Cu nanojunctions, resulting in an increased effective barrier height from 0.71 to 1.03 eV. This phenomenon, known as the pinch-off effect, is also applied to improve the performance of the planar n-Si/SiOx/Cu electrode via a PEC dissolution method that creates an inhomogeneous surface covered with CuOx. The Cu/CuSCN nanojunction still shows superior characteristics due to the favorable energetics of CuSCN. This work shows a rational route for engineering the surrounding layer to improve the performance of Si-based MIS photoelectrodes, enabled by the facile chemistry of coordination polymers

The solid-state mechanochemical reactions under ambient conditions of CuSCN and Zn(SCN)2 resulted in two novel materials: partially Zn-substituted α-CuSCN and a new phase CuxZny(SCN)x+2y. The reactions take place at the labile S-terminal, and both products show melting and glass transition behaviors. The optical band gap and solid-state ionization potential can be adjusted systematically by adjusting the Cu/Zn ratio. Density functional theory calculations also reveal that the Zn-substituted CuSCN structure features a complementary electronic structure of Cu 3d states at the valence band maximum and Zn 4s states at the conduction band minimum. This work shows a new route to develop semiconductors based on coordination polymers, which are becoming technologically relevant for electronic and optoelectronic applications.

Zr-based UiO-66 metal-organic framework (MOF) is one of the most studied MOFs with a wide range of potential applications. While UiO-66 is typically synthesized as a microcrystalline solid, we employ a particle downsizing strategy to synthesize UiO-66 as fluid gel with unique rheological properties, which allows the solution-based processing as sub-100 nm films and enhances the electrical conductivity of its pristine structure. Film thicknesses ranging from 40 to 150 nm could be achieved by controlling the spin-coating parameters. The generality of the method is also demonstrated for other Zr-based MOFs including MOF-801 and MOF-808. The impact of particle size and film thickness at the nanoscale on electrical properties of UiO-66 is shown to realize new features that are distinct from those of the bulk powder phase. An electrical insulator UiO-66 shows a significant increase in the electrical conductivity (10-5 S cm-1 compared to 10-7 S cm-1 in the bulk powder phase) when the 10 nm particles are distributed on the substrate with a thickness less than 100 nm. The findings establish a new route for processing of MOF materials as thin films with fine-tuned thickness and offer a new perspective for transport properties of Zr-based MOFs without structural modification.

Copper(I) thiocyanate (CuSCN) has been widely used as a hole-transport layer in organic optoelectronic devices. However, being a coordination polymer, its solution-processing is not straightforward; the typical process requires sulfide-based solvents that strongly interact with Cu(I). Herein, we show that a simple step of washing the CuSCN HTL with antisolvents, specifically acetone (Ace) or tetrahydrofuran (THF), can significantly increase the short-circuit current (Jsc) and fill factor (FF) of organic photovoltaic (OPV) cells. The treatment leads to an increase in the average power conversion efficiency (PCE) from 8.18% for OPV devices based on untreated CuSCN to 9.16% and 9.25% for cells based on Ace- and THF-treated CuSCN HTL, respectively. Furthermore, for organic light-emitting diodes (OLEDs) based on CuSCN HTL, the treatment by THF also increases the external quantum efficiency (EQE) from 5.2% to 8.2%. The facile antisolvent treatment can be readily applied to the solution-processing of CuSCN which is already employed in various organic optoelectronic devices.

Four donor–acceptor (D–A) type organic semiconductors, consisting of 5-hexylthiophene with thiophene/furan flanked benzothiadiazole/naphthothiadiazole, were investigated for organic field effect transistor (OFET) application. Despite being an analogue of thiophene, furan has received less attention in organic electronics due to its dissimilar properties to thiophene and instability in photochemical oxidation. Nevertheless, this study determines that furan could display comparable charge transport properties to its analogue. The extension of the electron-accepting thiadiazole core with the benzo group and different heteroatom flanking groups were investigated to show that the performance of OFETs is dependent on the molecular orbital, geometry, and packing. Bottom-gate bottom-contact device configuration was used to study the OFET transport properties of all the molecules. We successfully proved that a furan unit is a promising building block with a mobility (μmax) of 0.0122 cm2 V−1 s−1 for devices employing furan-substituted benzothiadiazole as the channel layer.

Solid‐state transistor sensors that can detect biomolecules in real time are highly attractive for emerging bioanalytical applications. However, combining upscalable manufacturing with the required performance remains challenging. Here, an alternative biosensor transistor concept is developed, which relies on a solution‐processed In2O3/ZnO semiconducting heterojunction featuring a geometrically engineered tri‐channel architecture for the rapid, real‐time detection of important biomolecules. The sensor combines a high electron mobility channel, attributed to the electronic properties of the In2O3/ZnO heterointerface, in close proximity to a sensing surface featuring tethered analyte receptors. The unusual tri‐channel design enables strong coupling between the buried electron channel and electrostatic perturbations occurring during receptor–analyte interactions allowing for robust, real‐time detection of biomolecules down to attomolar (am) concentrations. The experimental findings are corroborated by extensive device simulations, highlighting the unique advantages of the heterojunction tri‐channel design. By functionalizing the surface of the geometrically engineered channel with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) antibody receptors, real‐time detection of the SARS‐CoV‐2 spike S1 protein down to am concentrations is demonstrated in under 2 min in physiological relevant conditions., A solution‐processed metal oxide heterojunction channel with a geometrically engineered tri‐channel architecture several millimeters in size, is developed and used as a generic platform for robust, selective, and ultrasensitive detection of various biomolecules. As a proof‐of‐concept, selective sensing of the SARS‐CoV‐2 spike protein down to attomolar concentrations in under 2 min is demonstrated.

Undoped and Nb-doped TiO

The solid-state mechanochemical reactions under ambient conditions of CuSCN and Zn(SCN)2 resulted in two novel materials: partially Zn-substituted α-CuSCN and a new phase CuxZny(SCN)x+2y. The reactions take place at the labile S-terminal, and both products show melting and glass transition behaviors. The optical band gap and solid-state ionization potential can be adjusted systematically by adjusting the Cu:Zn ratio. Density functional theory calculations also reveal that the Zn-substituted CuSCN structure features a complementary electronic structure of Cu 3d states at the valence band maximum (VBM) and Zn 4s states at the conduction band minimum (CBM). This work shows a new route to develop semiconductors based on coordination polymers which are becoming technologically relevant for electronic and optoelectronic applications.

Looking beyond energy harvesting, metal-halide perovskites offer great opportunities to revolutionise large-area photodetection technologies due to their high absorption coefficients, long diffusion lengths, low trap densities and simple processability. However, successful extraction of photocarriers from perovskites and their conversion to electrical signals remain challenging due to the interdependency of photogain and dark current density. Here we report hybrid hetero-phototransistors by integrating perovskites with organic semiconductor transistor channels to form either “straddling-gap” type-I or “staggered-gap” type-II heterojunctions. Our results show that gradual transforming from type-II to type-I heterojunctions leads to increasing and tuneable photoresponsivity with high photogain. Importantly, with a preferential edge-on molecular orientation, the type-I heterostructure results in efficient photocarrier cycling through the channel. Additionally, we propose the use of a photo-inverter circuitry to assess the phototransistors’ functionality and amplification. Our study provides important insights into photocarrier dynamics and can help realise advanced device designs with “on-demand” optoelectronic properties., Realizing phototransistors based on hybrid perovskite heterostructures with tuneable photodetection remains a challenge. Here, the authors integrate metal-halide perovskites into organic semiconductors to design hybrid heterojunction phototransistors with state-of-the-art performance.

Semiconductors based on tin(II) show promising hole-transport characteristics due to the 5s electrons that form the valence band. In this paper, we report the synthesis and comprehensive characterization of tin(II) thiocyanate [Sn(NCS)2] and identify it as a novel transparent coordination polymer semiconductor. The single crystal X-ray analysis reveals covalently-bonded 1D polymeric chains that form a 2D structure through Sn–S tetrel bonds. Density functional theory calculations also confirm the importance of the van der Waals interactions between the 2D sheets. Furthermore, we show that the s character of Sn(II) is maintained at the top of the valence band, resulting in dispersed states with a small hole effective mass. The coordination with NCS ligands also leads to a conduction band which is high in energy, giving rise to a wide band gap and excellent transparency in the visible spectrum. This is the first report on the electronic properties of Sn(NCS)2 which highlights the potential of developing new transparent semiconductors based on thiocyanate coordination polymers.

Copper(I) thiocyanate (CuSCN) is a promising semiconductor with an expansive range of applications already demonstrated. Belonging to the group of coordination polymers, its structure can be easily modified, for example via ligand (L) coordination. In this work, we have analyzed in detail the crystal structures of 26 CuSCN–L complexes that exhibit diverse structures changing from the 3D networks of the parent CuSCN to 2D sheet, 1D ladder, 1D zigzag chain, 1D helical chain, and a 0D monomer as well as intermediate bridged structures. We outline herein the basic structural design principles based on four factors: (1) Cu(I) geometry, (2) CuSCN : L ratio, (3) steric effects, and (4) supramolecular interactions. In addition, we employ density functional theory to study the electronic structures of these 26 complexes and find that the opto/electronic properties vary over a wide range, e.g., widened or reduced fundamental band gaps, restricted hole transport due to Cu–SCN network disruption, and the possibility of electron transport through the ligand states. We also observe a correlation between the electronic properties and the dimensionality of the Cu–SCN network. Lowering the dimensionality of the 3D structure to 2D, 1D, and 0D by increasing the number of coordinating ligands, the dispersion and the width of the top valence bands decrease whereas the energy difference between the Cu and SCN states expands. Aliphatic ligands in most cases do not generate electronic states in the band gaps whereas aromatic ligands give rise to states between the Cu and SCN states that lead to optical absorption and emission in the visible range. This study provides guidelines for developing coordination polymer semiconductors based on the Cu–SCN network. The 2D structure is identified as a promising platform for designing new CuSCN-based materials as it retains the carrier transport properties while allowing for properties tailoring through ligand coordination.

We report the application of a coordination polymer semiconductor, tin(II) thiocyanate [Sn(SCN)$_2$] as an ultrathin anode interlayer in organic photovoltaics (OPVs). Sub-10 nm layers of Sn(SCN)$_2$ with high smoothness and excellent transparency having an optical band gap of 3.9 eV were deposited from an alcohol-based solution at room temperature without post-deposition annealing. Inserting Sn(SCN)$_2$ as an anode interlayer in polymer:fullerene OPVs drastically reduces the recombination loss due to the exciton-blocking energy levels of Sn(SCN)$_2$. At the optimum thickness of 7 nm, an average power conversion efficiency (PCE) of 7.6% and a maximum of 8.1% were obtained. The simple processability using common solvents gives Sn(SCN)$_2$ a distinct advantage over the more well-known copper(I) thiocyanate (CuSCN). The electronic and optical properties of Sn(SCN)$_2$ make it interesting for applications in large-area electronic devices., Accepted version. Article has been revised based on peer review comments. Photoelectron spectroscopy result (Fig. 4) after ion etching has been removed as it was determined that the etching depth was not sufficient and replaced with data of two different thicknesses (50 and 90 nm) of the bulk-heterojunction layer. The discussion on band-bending of version 1 has been amended

Solid-state transistor sensors that can detect biomolecules in real time are highly attractive for emerging bioanalytical applications. However, combining cost-effective manufacturing with high sensitivity, specificity and fast sensing response, remains challenging. Here we develop low-temperature solution-processed In2O3/ZnO heterojunction transistors featuring a geometrically engineered tri-channel architecture for rapid real-time detection of different biomolecules. The sensor combines a high electron mobility channel, attributed to the quasi-two-dimensional electron gas (q2DEG) at the buried In2O3/ZnO heterointerface, in close proximity to a sensing surface featuring tethered analyte receptors. The unusual tri-channel design enables strong coupling between the buried q2DEG and the minute electronic perturbations occurring during receptor-analyte interactions allowing for robust, real-time detection of biomolecules down to attomolar (aM) concentrations. By functionalizing the tri-channel surface with SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) antibody receptors, we demonstrate real-time detection of the SARS-CoV-2 spike S1 protein down to attomolar concentrations in under two minutes.

In anatase TiO2, various passivated co-dopants such as (V–N), (Mo–C), (Nb–N), (Ta–N), and (F–N) are of significant interest due to their enhanced photocatalytic activities under visible light. Unlike the bulk phase, the effect of co-dopants in TiO2 nanoparticles still lacks fundamental exploration. To understand this, we perform density-functional-theory calculations within the PBE generalized gradient approximation with corrections for the on-site Coulomb interaction (PBE + U) as well as hybrid functional (HSE06) approaches to investigate potential co-doping species and their locations in TiO2 nanoparticles that could be suitable for applications as antibacterial agents or for the degradation of organic pollutants. To allow an effective comparison with experiments, the criteria are set based on the experimentally measured band edge positions of TiO2 nanoparticles and the redox potentials of the reactive oxygen species of interest. Based on the analysis of donor and acceptor levels derived from thirty co-dopants, we find that the vanadium-nitrogen (VTi–NO) pair in the T2 configuration is the most suitable passivated co-dopant for enhanced photocatalytic activity as it can reduce the band gap of TiO2 nanoparticles while still providing a thermodynamic driving force for redox reactions to generate reactive oxygen species.

International audience; Metal–insulator–semiconductor (MIS) junctions based on n-Si have proven to be effective electrodes in terms of electrocatalysis activity and durability for performing photoelectrochemical water oxidation. Here, we show that the modification of n-Si MIS systems with CoFe Prussian blue (CoFePB) and NiRu Prussian blue (NiRuPB) analogues can modify their properties and allow a direct probing of the interfacial energetics through their redox feature. Our investigations demonstrate the importance of the preparation route and attribute the large upward photovoltage variation found in n-Si/SiOx/Ni/NiRuPB to the increasing inhomogeneity of the metal thin film. Finally, the optimal photoanode was tested for oxygen evolution and urea oxidation reactions. Our findings provide important insights on MIS photoanodes for future development in the field of solar fuel production.

Looking beyond energy harvesting, metal-halide perovskites offer great opportunities to revolutionise large-area photodetection technologies due to their high absorption coefficients, long diffusion lengths, low trap densities and simple processability. However, successful extraction of photocarriers from perovskites and their conversion to electrical signals remain challenging due to the interdependency of photogain and dark current density. Here we report hybrid hetero-phototransistors by integrating perovskites with organic semiconductor transistor channels to form either "straddling-gap" type-I or "staggered-gap" type-II heterojunctions. Our results show that gradual transforming from type-II to type-I heterojunctions leads to increasing and tuneable photoresponsivity with high photogain. Importantly, with a preferential edge-on molecular orientation, the type-I heterostructure results in efficient photocarrier cycling through the channel. Additionally, we propose the use of a photo-inverter circuitry to assess the phototransistors' functionality and amplification. Our study provides important insights into photocarrier dynamics and can help realise advanced device designs with "on-demand" optoelectronic properties.

This study assessed the potential of renewable energy (RE) resources to find a province in Thailand that could be a model city of complete relying upon RE. Here, Krabi province is a case study due to its abundance in RE resources. Based on the results of this study, Krabi has quantitative potential to produce 140 MW of electrical power from renewable energy, which is sufficient for the electricity demand in Krabi (95 MW). However, considering the economics, more than half of these 140 MW, which is from the palm trunks and fronds, is not worth investing. This leaves only fractions of palm bunch/palm fiber, biogas and solar (rooftop) dependable energy sources, accounting for approximately 60 MW, or 63% of electricity demand in Krabi.

While the effects of structural disorder on the electronic properties of solids are poorly understood, it is widely accepted that spatially isotropic orbitals lead to robustness against disorder. In this paper, we use first-principles calculations to show that a cluster of occupied bands in the coordination polymer semiconductor β-copper(I) thiocyanate undergo relatively little fluctuation in the presence of thermal disorder-a surprising finding given that these bands are composed of spatially anisotropic d-orbitals. Analysis with the tight-binding method and a stochastic network model suggests that the robustness of these bands to the thermal disorder can be traced to the way in which these orbitals are aligned with respect to each other. This special alignment causes strong inverse statistical correlations between orbital-orbital distances, making these bands robust to random fluctuations of these distances. As well as proving that disorder-robust electronic properties can be achieved even with anisotropic orbitals, our results provide a concrete example of when simple 'averaging' methods can be used to treat thermal disorder in electronic structure calculations.

Spinel cobalt oxide Co3O4 has broad light absorption that extends into the near-infrared, making it promising for photoelectrochemical applications (PEC). However, its PEC water reduction performance is modest, and the reason for this has not been clearly explained. In this work, we compare the PEC water reduction performance of Co3O4 photocathodes prepared by two different routes, electrodeposition and spin-coating, and investigate their optical and electronic properties in detail. Despite the two types of Co3O4 films having different interfacial morphologies, surface areas, and optical absorbances, both yield limited photocurrent densities of 6.5 μA cm−2. The reason for the low PEC water reduction performance of Co3O4 is elucidated by various spectroscopic techniques and ascribed to an unfavorable conduction band edge position. Thus, photogenerated electrons in Co3O4 lack the thermodynamic driving force to reduce water. This research identifies a fundamental characteristic of Co3O4 that is crucial in its development for PEC water reduction.

Metal thiocyanates, such as copper(I) thiocyanate (CuSCN) and tin(II) thiocyanate [Sn(SCN)2], are emerging as novel semiconductors for electronic applications, and while other thiocyanate coordination polymers are known, their electronic structures and properties have not been investigated. In this work, we employed density functional theory (DFT) and crystal orbital Hamilton population (COHP) to analyze the electronic structures and bonding character of 18 structures of 15 metal thiocyanate compounds as well as a main group thiocyanate, selenium thiocyanate [Se(SCN)2]. Interestingly, the ionic thiocyanates (groups 1 and 2) display band dispersions despite their valence and conduction bands (VBs and CBs) being derived mostly from the thiocyanate ligand. Thiocyanates of group 11 show the strongest contributions from the metals with their d electrons strongly dominating the top of the VBs. In contrast, metals from group 12 contribute their s electrons to the bottom CBs. Metals of groups 13 and 14 have lone pair electrons in the s orbitals, which are featured at the top of their VBs, while the metal p states contribute to the CBs. The bonding character and orbital contributions can be explained based on the trend in the electron binding energies of the coordinated atoms. The versatility of adjusting the orbital contribution by changing the metals can be used for tuning the electronic properties of semiconductors based on thiocyanate compounds.

We report a new simple way to improve the performance of a basic D–π–A organic dye in dye-sensitized solar cells (DSSCs) by donor substitutions on the π-linker of the dye. Three new molecularly engineered D–π–A dyes, namely T2-4, comprising triphenylamine (TPA) as a donor, terthiophene containing different numbers of TPA substitutions as a π-conjugated linker and cyanoacrylic acid as an acceptor, were synthesized and characterized. A detailed study on the effect of different dye structures on the performance of the DSSCs was conducted systematically using theoretical, photophysical, photovoltaic as well as photoelectrochemical methods and compared with that of the traditional D–π–A dye, namely T1. The introduction of electron donating TPA substitutes on the π-linker of the D–π–A dye were beneficial for a decrease of the electron recombination between redox electrolyte and the TiO2 surface as well as an increase of the electron correction efficiency, leading to improved open-circuit voltage (VOC) and short-circuit current (JSC). Consequently, DSSCs sensitized by dye T2 bearing one extra TPA substitution on the terminal thiophene ring of the π-linker delivered the best power conversion efficiency, reaching 8.08% at AM 1.5 simulated sunlight, a remarkable improvement of about 41% compared with 5.72% of T1 reference cells, owing to its high JSC and VOC. With the addition of CDCA as a coadsorbent, the best performing cells based on dye T2 exhibited an impressive conversion efficiency of 9.02% (JSC = 16.91 mA cm−2, VOC = 754 mV, FF = 0.705), exceeding that of the N719-based standard cell (8.20%). This renders the facile dye modification very promising to acquire simple effective organic dyes for high-efficiency DSSCs.

New (D–π–)2D–π–A-type dyes (CFTTnA, n = 2, 3) with a triarylamine as electron donor, a cyanoacrylic acid as both electron acceptor and anchoring group, and two π-conjugated 2-[7-(3,6-di-tert-butylcarbazol-9-yl)-9,9-dihexylfluoren-2-yl]thiophenes as N-aryl substituents on the amine donor as co-donors have been synthesized and characterized. Compared with a traditional D–π–A-type dye, these dyes exhibit broader absorption spectra and higher molar extinction coefficients as well as significantly enhanced photovoltaic performances. A power conversion efficiency of 6.64 % was achieved for a dye-sensitized solar cell (DSSC) based on CFTT3A. Theoretical calculations and electrochemical impedance spectroscopic investigations revealed the mechanism of the enhanced dye properties and cell performances.

A series of novel organic dyes (CPhTnPA, n = 0–2) with the D–D–π–A structural configuration incorporating carbazol-N-yl phenothiazine moiety as a donor (D–D) unit, phenyl oligothiophenes as a π-linker and cyanoacrylic acid as both electron-acceptor and anchoring group were synthesized and characterized for dye sensitized solar cells. Detailed investigation on the relationship between the structure, spectral and electrochemical properties, and performance of DSSC was described here. Time dependent density functional theory (TDDFT) calculations have been performed on the dyes, and the results showed that both electron donors (D–D) can contribute to electron injection upon photo-excitation, either directly or indirectly by internal conversion to the lowest excited state. Dye-sensitized solar cells (DSSCs) using dyes as the sensitizers exhibited good efficiencies. In virtue of co-sensitization, the CPhT2PA based solar cell can achieve photovoltaic efficiency as high as 7.78% (JSC = 15.22 mA cm−2, VOC = 0.74 V and FF = 0.69) which reached 95% with respect to that of the reference N719-based device (8.20%) in parallel investigations.

Photocatalytic degradation of organic pollutants is a promising way to clean wastewater. Herein, we develop and compare two processes for fabricating nanofibrous membranes with photocatalytic properties. Hybrid nanofibers are produced by colloid-electrospinning and composed of metal oxide nanoparticles on sintered SiO2 nanoparticles. The latter serves as support for the photocatalyst and preserves the structural integrity of nanofibers. Adsorption of metal salts on crosslinked polymer/SiO2 fibers followed by calcination allows for the obtention of fibers with large amounts of metal oxide. Nanofibrous membranes with supported ZnO, In2O3, or mixture of both, display photocatalytic activity upon UV irradiation. The membranes can degrade a dye and an organophosphate pesticide more effectively than membranes directly fabricated from the calcination of metal oxides.

Ultra-small and monodispersed zinc sulfide nanocrystals (NCs) (d ≤ 3 nm) have been prepared without the use of any surfactants by a synthetic route using benzyl mercaptan as a source of sulfur. The prepared NCs are dispersible in highly polar solvents and display the capability to closely pack-up in a bulky film. The NCs were characterized by TEM, XRD and UV-vis optical absorption as well as by steady-state and time-resolved photoluminescence (PL) spectroscopies. Uniform films of ZnS were spin-coated on glass and ITO-glass substrates using a NCs dispersion in N,N-dimethylformamide. The NCs and the resulting films were characterized by morphological and optoelectronic probing techniques such as AFM, SEM, diffuse reflectance, PL and photoelectron spectroscopy in air. These physical investigations confirmed that the chalcogenide NCs grown by this method have the potential to be utilized directly as photocatalysts and are potentially useful building-blocks/starting materials for the fabrication of semiconductor thin films for optoelectronic applications such as LED, luminescent screens, field effect transistor and solar cells. Insights on the chemistry involved in the NCs growth have been provided revealing that their formation proceeds through a mechanism involving a thioether elimination reaction.

Following the unprecedented rise in photovoltaic power conversion efficiencies during the past five years, metal-halide perovskites (MHPs) have emerged as a new and highly promising class of solar-energy materials. Their extraordinary electrical and optical properties combined with the abundance of the raw materials, the simplicity of synthetic routes, and processing versatility make MHPs ideal for cost-efficient, large-volume manufacturing of a plethora of optoelectronic devices that span far beyond photovoltaics. Herein looks beyond current applications in the field of energy, to the area of large-area electronics using MHPs as the semiconductor material. A comprehensive overview of the relevant fundamental material properties of MHPs, including crystal structure, electronic states, and charge transport, is provided first. Thereafter, recent demonstrations of MHP-based thin-film transistors and their application in logic circuits, as well as bi-functional devices such as light-sensing and light-emitting transistors, are discussed. Finally, the challenges and opportunities in the area of MHPs-based electronics, with particular emphasis on manufacturing, stability, and health and environmental concerns, are highlighted.

This study reports the development of copper(I) thiocyanate (CuSCN) hole-transport layers (HTLs) processed from aqueous ammonia as a novel alternative to conventional n-alkyl sulfide solvents. Wide bandgap (3.4–3.9 eV) and ultrathin (3–5 nm) layers of CuSCN are formed when the aqueous CuSCN–ammine complex solution is spin-cast in air and annealed at 100 °C. X-ray photoelectron spectroscopy confirms the high compositional purity of the formed CuSCN layers, while the high-resolution valence band spectra agree with first-principles calculations. Study of the hole-transport properties using field-effect transistor measurements reveals that the aqueous-processed CuSCN layers exhibit a fivefold higher hole mobility than films processed from diethyl sulfide solutions with the maximum values approaching 0.1 cm2 V−1 s−1. A further interesting characteristic is the low surface roughness of the resulting CuSCN layers, which in the case of solar cells helps to planarize the indium tin oxide anode. Organic bulk heterojunction and planar organometal halide perovskite solar cells based on aqueous-processed CuSCN HTLs yield power conversion efficiency of 10.7% and 17.5%, respectively. Importantly, aqueous-processed CuSCN-based cells consistently outperform devices based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate HTLs. This is the first report on CuSCN films and devices processed via an aqueous-based synthetic route that is compatible with high-throughput manufacturing and paves the way for further developments.

It is presented that the introduction of an alkyne linkage could be an important tool for fine-tuning the electronic and optoelectronic properties of certain donor–acceptor (D–A) conjugated polymers. Extensive optoelectronic studies in an alternating copolymer consisting of diketopyrrolopyrrole (DPP) and ethynylene linkage (TDPPTTB) and comparison over its fully cyclic DPP analogues, such as phenyl (TDPPTP) and thiophene (TDPPTT) rings reveals the role of the ethynylene moiety when it is introduced into the polymer backbone. The ethynylene moiety decreases the donor character of the thiophenes that flank the DPP therefore the highest occupied molecular orbital (HOMO) level of TDPPTTB is situated between the HOMO levels of the TDPPTP and TDPPTT. The optical band gap (Eoptg) of TDPPTTB is fixed between the Eoptg of TDPPTT and TDPPTP with a significant blue-shift in its absorption maximum. Furthermore, detailed studies on the electronic properties of TDPPTTB have been performed in Field Effect Transistors (FETs) using various dielectric materials. Transistors based on TDPPTTB films annealed at 120 °C show ambipolar behaviour, similar to TDPPTP and TDPPTT, with carrier mobilities of 0.03 cm2 V−1 s−1 for holes and 0.02 cm2 V−1 s−1 for electrons.

Funding text This work was partly supported by Fondazione Cariplo through the project INDIXI (Grant no. Ref.2011/0368 ). P.E.K. acknowledges the financial support of an Intra European Marie Curie Fellowship ( FP7-PEOPLE-2011-IEF project DELUMOPV) G.T. and G.C. acknowledge Fondazione Cariplo (projects 2009-2550 and 2010-1351 ) and project 5×1000 Junior 2011 for financial support. The authors would like to cordially thank Dr. M. R. Antognazza for offering access to her cw-PIA experimental set-up. Herein we present a methodology for improving the power conversion efficiency of organic solar cells made by photoactive layers of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PCBM) of non-optimized microstructure. In our study we achieve a 47% improvement in the power conversion efficiency (PCE) of the device by utilizing a thiophene-based quinoid (QBT) moiety as the third component in the P3HT:PCBM:QBT photoactive layers. Based on a set of independent characterization experiments we address the QBT composition dependent photophysical, electrical, thermal, structural and morphology-related properties of the ternary photovoltaic P3HT:PCBM:QBT system for elucidating the origin of the PCE improvement. In small amounts (0.3-0.6 wt%), QBT serves as a nucleation agent, it enlarges the size of the P3HT crystallites by 15% and it increases the fraction of well-ordered P3HT chains in the P3HT:PCBM:QBT layer. The improved microstructure of the photoactive layer in combination with the QBT-assisted photo-induced hole transfer step from PCBM to P3HT, lead to an increase of the charge photogeneration yield in the P3HT:PCBM:QBT triple bulk heterojunction. The relatively small optical gap of QBT facilitates a resonant energy transfer step from the photoexcited PCBM to the QBT followed by a charge transfer process between QBT and the P3HT matrix. Based on these findings we propose general guidelines for the design of next generation functional additives to be used in organic photovoltaics. © 2013 Elsevier B.V.

A series of donor–acceptor (D–A) conjugated polymers utilizing 4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophene (DTG) as the electron rich unit and three electron withdrawing units of varying strength, namely 2-octyl-2H-benzo[d][1,2,3]triazole (BTz), 5,6-difluorobenzo[c][1,2,5]thiadiazole (DFBT) and [1,2,5]thiadiazolo[3,4-c]pyridine (PT) are reported. It is demonstrated how the choice of the acceptor unit (BTz, DFBT, PT) influences the relative positions of the energy levels, the intramolecular transition energy (ICT), the optical band gap (Egopt), and the structural conformation of the DTG-based co-polymers. Moreover, the photovoltaic performance of poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl)-([1,2,5]thiadiazolo[3,4-c]pyridine)] (PDTG-PT), poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl)-(2-octyl-2H-benzo[d][1,2,3]triazole)] (PDTG-BTz), and poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl)-(5,6-difluorobenzo[c][1,2,5]thiadiazole)] (PDTG-DFBT) is studied in blends with [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM). The highest power conversion efficiency (PCE) is obtained by PDTG-PT (5.2%) in normal architecture. The PCE of PDTG-PT is further improved to 6.6% when the device architecture is modified from normal to inverted. Therefore, PDTG-PT is an ideal candidate for application in tandem solar cells configuration due to its high efficiency at very low band gaps (Egopt = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co-polymers containing bridged bithiophenes with 5-member fused rings in the central core and possessing an Egopt below 1.4 eV.

The wide bandgap and highly transparent inorganic compound copper(I) thiocyanate (CuSCN) is used for the first time to fabricate p-type thin-film transistors processed from solution at room temperature. By combining CuSCN with the high-k relaxor ferroelectric polymeric dielectric P(VDF-TrFE-CFE), we demonstrate low-voltage transistors with hole mobilities on the order of 0.1 cm(2) V(-1) s(-1) . By integrating two CuSCN transistors, unipolar logic NOT gates are also demonstrated.

We report the synthesis of two novel cyclopenta[2,1-b:3,4-b′]dithiophen-4-one monomers containing solubilizing alkyl groups in the peripheral 3,5 positions. Polymerization with (E)-1,2-bis(tributylstannyl)-ethylene under Stille coupling conditions afforded the first reported examples of soluble poly(cyclopentadithiophen-4-one)vinylenes. The resulting polymers absorb in the near-infrared, with a maximum thin film absorbance around 815 nm and have optical band gaps of 1.25 eV. The polymers exhibit promising ambipolar field effect transistor performance, with average saturated mobilities of 0.5 cm2 V–1 s–1 for holes and 0.12 cm2 V–1 s–1 for electrons. The ambipolar transistors operate in both the hole and electron transport regimes in ambient air. Prolonged exposure to ambient atmosphere leads to a gradual loss of the electron transport behavior, with little change observed in the p-type mobility.

We report the fabrication of light-sensing thin-film transistors based on solution processed films of ZnO, as the channel material, functionalized with an organic dye as the light sensitizer. Due to the presence of the dye, the hybrid devices show exceptionally high photosensitivity to green light of 10 6 and a maximum photoresponsivity on the order of 10 4 A/W. The high performance is argued to be the result of the grain barrier limited nature of electron transport across the polycrystalline ZnO film and its dependence on charge carrier density upon illumination with green light. In addition to the excellent photoresponsivity and signal gain, the hybrid ZnO-dye photoactive layer exhibits high optical transparency. The unique combination of simple device fabrication and distinctive physical characteristics, such as optical transparency, renders the technology attractive for application in large-area transparent photodetectors. © 2012 American Institute of Physics.

We report the development of dye-sensitized thin-film phototransistors consisting of an ultrathin layer (10 nm) of indium oxide (In2O3) the surface of which is functionalized with a self-assembled monolayer of the light absorbing organic dye D102. The resulting transistors exhibit a preferential color photoresponse centered in the wavelength region of ∼500 nm with a maximum photosensitivity of ∼10(6) and a responsivity value of up to 2 × 10(3) A/W. The high photoresponse is attributed to internal signal gain and more precisely to charge carriers generated upon photoexcitation of the D102 dye which lead to the generation of free electrons in the semiconducting layer and to the high photoresponse measured. Due to the small amount of absorption of visible photons, the hybrid In2O3/D102 bilayer channel appears transparent with an average optical transmission of92% in the wavelength range 400-700 nm. Importantly, the phototransistors are processed from solution-phase at temperatures below 200 °C hence making the technology compatible with inexpensive and temperature sensitive flexible substrate materials such as plastic.

The quality of the gate dielectric/semiconductor interface in thin-film transistors (TFTs) is known to determine the optimum operating characteristics attainable. As a result in recent years the development of methodologies that aim to improve the channel interface quality has become a priority. Herein, we study the impact of the surface morphology of three solution-processed high-k metal oxide dielectrics, namely AlOx, HfOx, and ZrOx, on the operating characteristics of In2O3 TFTs. Six different dielectric configurations were produced via single or double-step spin-casting of the various precursor formulations. All layers exhibited high areal capacitance in the range of 200 to 575 nF/cm2, hence proving suitable, for application in low-voltage n-channel In2O3 TFTs. Study of the surface topography of the various layers indicates that double spin-cast dielectrics exhibit consistently smoother layer surfaces and yield TFTs with improved operating characteristics manifested, primarily, as an increase in the electron mobility (μ). To this end, μ is found to increase from 1 to 2 cm2/Vs for AlOx, 1.8 to 6.4 cm2/Vs for HfOx, and 2.8 to 18.7 cm2/Vs for ZrOx-based In2O3 TFTs utilizing single and double-layer dielectric, respectively. The proposed method is simple and potentially applicable to other metal oxide dielectrics and semiconductors.

We report on low operating voltage thin-film transistors (TFTs) and integrated inverters based on copper(I) thiocyanate (CuSCN) layers processed from solution at low temperature on freestanding plastic foils. As-fabricated coplanar bottom-gate and staggered top-gate TFTs exhibit hole-transporting characteristics with average mobility values of 0.0016 cm2 V1 s 1 and 0.013 cm2 V1 s 1 , respectively, current on/off ratio in the range 102 –104 , and maximum operating voltages between 3.5 and 10 V, depending on the gate dielectric employed. The promising TFT characteristics enable fabrication of unipolar NOT gates on flexible free-standing plastic substrates with voltage gain of 3.4 at voltages as low as 3.5 V. Importantly, discrete CuSCN transistors and integrated logic inverters remain fully functional even when mechanically bent to a tensile radius of 4 mm, demonstrating the potential of the technology for flexible electronics.

Three novel polythiophene isomers are reported whereby the only difference in structure relates to the regiochemistry of the solubilizing side chains on the backbone. This is demonstrated to have a significant impact on the optoelectronic properties of the polymers and their propensity to aggregate in solution. These differences are rationalized on the basis of differences in backbone torsion. The polymer with the largest effective conjugation length is demonstrated to exhibit the highest field-effect mobility, with peak values up to 4.6 cm(2) V(-1) s(-1).