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Conjugated polymers incorporating glycolated side chains have been widely used for those organic electronic devices that use the properties of the doped state, such as organic thermoelectrics (OTEs) and organic electrochemical transistors (OECTs). This work pioneers the study of adjusting the molecular weight of such conjugated polymers for optimizing the electronic transport of both OTE and OECT devices. The example conjugated polymer P-3O has a naphthalene-alt-bithiazole-based backbone bearing polar side chains. The molecular weight of P-3O was tuned from Mw = 37 kDa to Mw = 81 kDa by controlling the polymerization conditions. The molecular weight strongly influenced the crystalline domain size and π-stacking paracrystallinity, while the interaction between polar side chains and the dopant molecules largely dictates the doping. This finding seems simple but is significant as it enables us to individually control free charge density and mobility in the doped state. As such, an appropriate molecular weight (Mw = 68 kDa) promotes the formation of broad charge transport pathways, leading to the best thermoelectric performance (σ ≈ 7 S cm−1 and PF ≈ 25 μW m−1 K−2) and the highest μC* ≈ 27 F cm−1 V−1 s−1 for OECT devices. This study proves the strength of regulating molecular weight to enhance electronic transport in extrinsically-doped conjugated polymers. [ABSTRACT FROM AUTHOR]

Ensuring the chemical, physical, and microbial safety of food and ingredients underpins the international trade of food items and is integral to building consumer confidence. Achieving this requires effective systems to support the safety of food across the supply chain. Differing risk‐assessment approaches are utilized globally for establishing food safety systems, and bench marking these approaches against international food safety standards can assist in the development of country‐specific systems. This China–Australia collaborative review examined similarities and differences in the food safety risk‐assessment systems of China, Australia/New Zealand, Canada, and the United States, with the view to identify areas that could support improvements to the Chinese system. Key differences include the level of cohesiveness among stakeholders and the level to which each country promotes the international harmonization of standards. The evidence highlights a need for greater capacity‐building in risk assessment in China that may support greater stakeholders' cohesion, improve hazard identification, and allow regulators to more readily keep abreast of changes to international standards. This review may help the Chinese food industry to replicate the same level of food safety risk assessment currently applied by other key countries, and reflects the determination, government prioritization, and active strengthening of China's National Centre for Food Safety Risk Assessment currently underway. [ABSTRACT FROM AUTHOR]

Hummelen et al. for the first time reported the synthetic route and characterization of a soluble methanofullerene derivative in 1995. In the same year, such a fullerene derivative was successfully used as the acceptor of internal donor–acceptor heterojunctions in the field of organic photovoltaics (OPV). Since then, it has opened an era of fullerene derivatives towards OPV application until 2015. Beyond OPV, several new research directions for solution-processable fullerene derivatives recently appeared, including perovskite solar cells, organic thermoelectrics, molecular electronics, and organic electrochemical transistors. This review highlights the important role of fullerene derivatives in these emerging research areas and summarizes the recent progress in the development of fullerene derivatives in these new research fields. These fields require fullerene derivatives with new properties, such as strong electron-donating ability, large polarity, or excellent water permeability. Therefore, new design strategies of fullerene derivatives and device engineering considerations are desired. [ABSTRACT FROM AUTHOR]

The photophysics of 2D perovskites incorporating 1,4‐phenylenedimethanammonium (PDMA) as spacer cations is studied. PDMAPbI4 and PDMASnI4 exhibit absorption and luminescence spectra dominated by excitonic transitions and an emission due to two different states. Low‐temperature studies reveal a time‐dependent red shift of 12 meV that is correlated with grain‐specific luminescence spectra observed in optical micrographs. For the Pb‐variant, grains of red‐shifted and lower intensity band edge emission simultaneously exhibit a more pronounced luminescence from a broad defect‐related band around 2 eV. This suggests the grain‐specific emission to be related to local defects. These observations have important consequences for the understanding of luminescence of 2D perovskites, for which peak splitting of the band edge emission is a common, yet not completely resolved observation. [ABSTRACT FROM AUTHOR]

2D/3D mixed tin perovskites have the advantages of high crystallinity and preferential orientation compared to pure 3D tin perovskite. However, solar cells based on 2D/3D mixed tin perovskites are still limited by low power conversion efficiency (PCE) when compared to their lead-based counterparts. It is essential to gain deeper insight into the factors that limit the performance of these solar cells in order to further improve them. In this work, we demonstrate that the starting stoichiometry of 2D/3D (PEA0.08FAxSnI3) tin perovskite films influences their crystallization and photophysical properties as well as the solar cell performance. The reference 2D/3D film (x = 0.92, where x refers to the stoichiometry of the precursors) is highly crystalline with the 3D phase preferentially oriented and a small amount of 2D phase located at the bottom of the film. The reference solar cell delivers a PCE of about 8.0%. 2D/3D films with even higher FA concentration (x > 1.0) mainly consist of poorly crystalline and randomly oriented 3D phases, with much higher trap density compared to the reference film. The corresponding solar cells therefore suffer from severe trap-assisted charge recombination, and deliver a poor PCE of <1%. FA-deficient 2D/3D films (x ≤ 0.8) form highly crystalline and oriented 3D grains, and at the same time a large quantity of 2D (n ≤ 2) phases throughout the entire film. Furthermore, the FA-deficient films contain excess SnI2. Consequently, charge transport in FA-deficient films is hindered by both the 2D phases oriented parallel to the substrate and SnI2, and the corresponding solar cells suffer from the recombination of free holes and electrons, resulting in a lower PCE than the reference devices. [ABSTRACT FROM AUTHOR]

Metal halide Ruddlesen–Popper perovskite solar cells (RPPSCs) have attracted a great deal of attention in the research community due to their excellent stability over the 3D counterparts. In 2014, the first RPPSC was reported achieving a power conversion efficiency (PCE) of about 4.7%. To date, this type of solar cells reach a PCE exceeding 18% on lab scale. In this essay, distil strategies to further improve the PCE of RPPSCs are discussed. First, the unique physical properties of RPP are discussed to highlight the importance of film processing and material design, and then the factors that are limiting RPPSCs with special focus on the crystallographic and charge transport properties are addressed. Finally, the opportunities for RPPSCs are discussed, and opinions are provided regarding how to further improve the performance of these devices and on strategies which may advance the technology toward its industrial exploitation. [ABSTRACT FROM AUTHOR]

To date, there are no reports of 3D tin perovskite being used as a semiconducting channel in field‐effect transistors (FETs). This is probably due to the large amount of trap states and high p‐doping typical of this material. Here, the first top‐gate bottom‐contact FET using formamidinium tin triiodide perovskite films is reported as a semiconducting channel. These FET devices show a hole mobility of up to 0.21 cm2 V−1 s−1, an ION/OFF ratio of 104, and a relatively small threshold voltage (VTH) of 2.8 V. Besides the device geometry, the key factor explaining this performance is the reduced doping level of the active layer. In fact, by adding a small amount of the 2D material in the 3D tin perovskite, the crystallinity of FASnI3 is enhanced, and the trap density and hole carrier density are reduced by one order of magnitude. Importantly, these transistors show enhanced parameters after 20 months of storage in a N2 atmosphere. [ABSTRACT FROM AUTHOR]

Recently, a significant amount of attention went toward the development of artificial neural networks, as these promise efficient computation for specific tasks that are expensive or even impossible for von Neumann architecture‐based computers. A considerable amount of research is conducted to develop materials in which layered neural networks are easily implemented. Herein, the use of high‐quality semiconducting single‐walled carbon nanotube (s‐SWCNT) inks to fabricate artificial synapses using simple bottom‐gate field‐effect transistors (FETs) is reported. The synapse utilizes the otherwise often dreaded hysteresis, the characteristic of the device structure, and the materials used therein. This hysteresis spans several orders of magnitude. The SWCNT synaptic transistor exhibits a clear spike‐time‐dependent plasticity (STDP), indicating the ability to achieve learning, following a mechanism similar to biological systems: asymmetric anti‐Hebbian learning. The very well‐defined STDP shape, together with the use of a simple pulse shape to obtain it, has not been reported previously for synaptic transistors. This represents a crucial step for further development of actual hardware implementation of artificial synapses in a more extensive, layered network. Interestingly, the time response of the device is very similar to the one of biological synapse, opening opportunities unavailable to CMOS emulations. [ABSTRACT FROM AUTHOR]

Knowledge of the mechanism of formation, orientation, and location of phases inside thin perovskite films is essential to optimize their optoelectronic properties. Among the most promising, low toxicity, lead‐free perovskites, the tin‐based ones are receiving much attention. Here, an extensive in situ and ex situ structural study is performed on the mechanism of crystallization from solution of 3D formamidinium tin iodide (FASnI3), 2D phenylethylammonium tin iodide (PEA2SnI4), and hybrid PEA2FAn−1SnnI3n+1 Ruddlesden–Popper perovskites. Addition of small amounts of low‐dimensional component promotes oriented 3D‐like crystallite growth in the top part of the film, together with an aligned quasi‐2D bottom‐rich phase. The sporadic bulk nucleation occurring in the pure 3D system is negligible in the pure 2D and in the hybrid systems with sufficiently high PEA content, where only surface crystallization occurs. Moreover, tin‐based perovskites form through a direct conversion of a disordered precursor phase without forming ordered solvated intermediates and thus without the need of thermal annealing steps. The findings are used to explain the device performances over a wide range of composition and shed light onto the mechanism of the formation of one of the most promising Sn‐based perovskites, providing opportunities to further improve the performances of these interesting Pb‐free materials. [ABSTRACT FROM AUTHOR]

Low power conversion efficiency (PCE) and poor reproducibility are among the main challenges for tin-based perovskite solar cells (HPSCs). The facile formation of tin vacancies and oxidation of the divalent tin cation during the thin film fabrication process are among the causes of these problems, because the tin perovskite layer then becomes p-doped, resulting in significant trap-assisted recombination losses in devices. In this paper, we demonstrate that increasing the crystallinity of the tin perovskite film is an effective way to address the open issues with Sn-based perovskites. We succeed in improving the crystallinity of the 3D formamidinium tin iodide (FASnI 3) grains, increasing their size, and perfecting their orientation in the out-of-plane direction by incorporating ethylammonium iodide (EAI) into a 2D/3D tin perovskite film (where 2D is PEA 2 FASn 2 I 7 , PEA = phenylethylammonium). This leads to a decrease of traps and background charge carrier density, and therefore to decreased charge recombination losses in EA x 2D/3D based devices, as compared not only to devices based on FASnI 3 but also to those based on 2D/3D mixtures. As a consequence, devices using a perovskite layer with composition EA 0.08 2D/3D exhibit much higher PCE (8.4%) and better reproducibility compared to devices based on mixed 2D/3D perovskites (7.7%) and 3D perovskite (4.7%). Image 1 ● The crystallinity and orientation of the 3D formamidinium tin iodide grains is improved by incorporating ethylammonium cation into a 2D/3D tin perovskite film. ● The trap density and background charge carrier density are reduced by incorporating ethylammonium cation into a 2D/3D tin perovskite film. ● The charge recombination is reduced in the tin perovskite solar cells by incorporating ethylammonium cation into a 2D/3D tin perovskite film. ● The devices using ethylammonium modified 2D/3D tin perovskite layer exhibit much higher PCE (8.4%) and better reproducibility compared to devices based on either 2D/3D perovskites (7.7%) or 3D perovskite (4.7%) [ABSTRACT FROM AUTHOR]

Abstract: The low power conversion efficiency (PCE) of tin‐based hybrid perovskite solar cells (HPSCs) is mainly attributed to the high background carrier density due to a high density of intrinsic defects such as Sn vacancies and oxidized species (Sn4+) that characterize Sn‐based HPSCs. Herein, this study reports on the successful reduction of the background carrier density by more than one order of magnitude by depositing near‐single‐crystalline formamidinium tin iodide (FASnI3) films with the orthorhombic a‐axis in the out‐of‐plane direction. Using these highly crystalline films, obtained by mixing a very small amount (0.08 m) of layered (2D) Sn perovskite with 0.92 m (3D) FASnI3, for the first time a PCE as high as 9.0% in a planar p–i–n device structure is achieved. These devices display negligible hysteresis and light soaking, as they benefit from very low trap‐assisted recombination, low shunt losses, and more efficient charge collection. This represents a 50% improvement in PCE compared to the best reference cell based on a pure FASnI3 film using SnF2 as a reducing agent. Moreover, the 2D/3D‐based HPSCs show considerable improved stability due to the enhanced robustness of the perovskite film compared to the reference cell. [ABSTRACT FROM AUTHOR]

The mechanism behind the temperature dependence of the device performance in hybrid perovskite solar cells (HPSCs) is investigated systematically. The power conversion efficiency (PCE) of the reference cell using [60]PCBM as electron extraction layer (EEL) drops significantly from 11.9% at 295 K to 7% at 180 K. The deteriorated charge carrier extraction is found as the dominant factor causing this degradation. Temperature dependent spectroscopy and charge transport studies demonstrate that the poor electron transport in the [60]PCBM EEL at low temperature leads to inefficient charge carrier extraction. It is further demonstrated that the n-type doping of [60]PCBM EEL or the use of an EEL (fulleropyrrolidine with a triethylene glycol monoethyl ether side chain) with higher electron transport capability is an effective strategy to achieve HPSCs working efficiently over a broad temperature range. The devices fabricated with these highly performing EELs have PCEs at 180 K of 16.7% and 18.2%, respectively. These results support the idea that the temperature dependence of the electron transport in the EELs limits the device performance in HPSCs, especially at lower temperatures and they also give directions toward further improvement of the PCE of HPSCs at realistic operating temperatures. [ABSTRACT FROM AUTHOR]

Despite the rich experience gained in controlling the microstructure of perovskite films over the past several years, little is known about how the microstructure affects the device properties of perovskite solar cells (HPSCs). In this work, the effects of the perovskite film microstructure on the charge recombination and light-soaking phenomenon in mixed halide HPSCs are investigated. Devices with noncompact perovskite morphology show a severe light soaking effect, with the power conversion efficiency (PCE) improved from 3.7% to 11.6% after light soaking. Devices with compact perovskite morphology show a negligible light soaking effect, with PCE slightly increased from 11.4% to 11.9% after light soaking. From device investigations, photoluminescence, and impedance spectroscopy measurements, it is demonstrated that interface electron traps at the grain boundaries as well as at the crystal surface dominate the light soaking effect. Severe trap-assisted recombination takes place in HPSCs using noncompact films, while it is effectively eliminated in devices with compact films. Moreover, how the grain size of the perovskite film affects the light soaking phenomenon is investigated. In the case of compact perovskite films, the size of the grains has a limited effect on the light soaking. In these compact films, grains are fused and trap states are effectively reduced. [ABSTRACT FROM AUTHOR]

A solution-processed neutral hole transport layer is developed by in situ formation of MoO3 in aqueous PEDOT:PSS dispersion (MoO3-PEDOT:PSS). This MoO3-PEDOT:PSS composite film takes advantage of both the highly conductive PEDOT:PSS and the ambient conditions stability of MoO3; consequently it possesses a smooth surface and considerably reduced hygroscopicity. The resulting bulk heterojunction polymer solar cells (BHJ PSC) based on poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1):[6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) blends using MoO3-PEDOT:PSS composite film as hole transport layer (HTL) show considerable improvement in power conversion efficiency (PCE), from 5.5% to 6.4%, compared with the reference pristine PEDOT:PSS-based device. More importantly, the device with MoO3-PEDOT:PSS HTL shows considerably improved stability, with the PCE remaining at 80% of its original value when stored in ambient air in the dark for 10 days. In comparison, the reference solar cell with PEDOT:PSS layer shows complete failure within 10 days. This MoO3-PEDOT:PSS implies the potential for low-cost roll-to-roll fabrication of high-efficiency polymer solar cells with long-term stability at ambient conditions. [ABSTRACT FROM AUTHOR]

Abstract: Efficient photovoltaic (PV) cells based on regioregular poly(3-hexylthiophene) (P3HT):fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PC61BM) composites have been fabricated by using solution-processed molybdenum oxide (MoO3) as an anode buffer layer. The influence of solution-processed MoO3 anode buffer layer on the device performance of P3HT:PCBM PV cells is investigated as compared to the PV cells with different anode buffer layers including water-soluble poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and the thermally evaporated MoO3. It is found that .the performance of the PV cell with solution-processed MoO3 anode buffer layer is comparable or higher than the devices using PEDOT:PSS or thermally evaporated MoO3 as the anode buffer layer. The power conversion efficiency of PV cell with solution-processed MoO3 anode buffer layer reaches 3.14% under AM1.5G 100mW/cm2 illumination. [Copyright &y& Elsevier]

Abstract: The mechanisms for introduction of the additive to improve the poly(3-hexylthiophene) (P3HT):methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) organic solar cells performance are investigated. We add n-dodecylthiol to P3HT/PCBM solution and find that it both improves P3HT crystallinity and enhances P3HT/PCBM phase separation extent. UV–vis absorption spectroscopy (UV–vis) and dynamic light scattering (DLS) results reveal that n-dodecylthiol reduces the P3HT chains entanglement in the solution, which facilitates coil-to-rod transformation, a premise condition for P3HT crystallization. Also, it discloses that the influence of PCBM on the P3HT molecular interaction is diminished by adding n-dodecylthiol, this consequently benefits the P3HT crystallization during the film-forming process. Furthermore, the enhanced P3HT crystallinity reduces the PCBM amount which dissolved in the amorphous regions of P3HT, then promotes the aggregation of PCBM, which contributes to the controlled scale of phase segregation. Thus an increased P3HT crystallinity and a commensurate scale of phase separation balancing for exciton dissociation and charge transport and/or collection are finally obtained. This results in an almost threefold increase in device efficiencies when the volume fraction of additive is 2.0%, compared with reference devices without any additive in the photoactive layer as a consequence. [Copyright &y& Elsevier]

Solution-processed zinc oxide (ZnO) nanocrystal modified with titanium oxide (TiOX) precursor is introduced as cathode interfacial layer in inverted bulk-heterojunction polymer solar cells. The resultant inverted polymer solar cell exhibits an open-circuit voltage of 0.87 V, a fill factor of 0.67, and an overall power conversion efficiency of 6.53%, respectively, higher than those of the control cells with sole ZnO or TiOX as the cathode interfacial layers. Further studies verify that the improved morphology and electronic structure of ZnO-TiOX composite layer favors reducing shunt loss and interfacial charge recombination and hence enhancing the photovoltaic performance. [ABSTRACT FROM AUTHOR]

Crystal Formation: Mechanism of Crystal Formation in Ruddlesden-Popper Sn-Based Perovskites (Adv. Funct. Keywords: crystal orientation; film formation mechanism; in situ GIWAXS; Ruddlesden-Popper; spin coating; tin perovskite solar cells EN crystal orientation film formation mechanism in situ GIWAXS Ruddlesden-Popper spin coating tin perovskite solar cells 1 1 1 06/13/20 20200615 NES 200615 In article number 2001294, Maria A. Loi, Giuseppe Portale, and co-workers unveil the mechanism of crystallization of Ruddlesden-Popper Sn-based perovskites using in situ X-ray measurements. Crystal orientation, film formation mechanism, in situ GIWAXS, Ruddlesden-Popper, spin coating, tin perovskite solar cells. [Extracted from the article]

Organic–inorganic hybrid perovskite solar cells (HPSCs) have achieved an impressive power conversion efficiency (PCE) of 25.2% in 2019. At this stage, it is of paramount importance to understand in detail the working mechanism of these devices and which physical and chemical processes govern not only their power conversion efficiency but also their long‐term stability. The interfaces between the perovskite film and the charge transport layers are among the most important factors in determining both the PCE and stability of HPSCs. Herein, an overview is provided on the recent advances in the fundamental understanding of how these interfaces influence the performance of HPSCs. Firstly, it is discussed how the surface energy of the charge transport layer, the energy level alignment at the interfaces, the charge transport in interfacial layers, defects and mobile ions in the perovskite film, and interfacial layers or at the interfaces affect the charge recombination as well as hysteresis and light soaking phenomenon. Then it is discussed how the interfaces and interfacial materials influence the stability of HPSCs. At the same time, an overview is also provided on the various design strategies for the interfaces and the interfacial materials. At the end, the outlook for the development of highly efficient and stable HPSCs is provided. [ABSTRACT FROM AUTHOR]

Tin‐based perovskites have long remained a side topic in current perovskite optoelectronic research. With the recent efficiency improvement in thin film solar cells and the observation of a long hot carrier cooling time in formamidinium tin iodide (FASnI3), a thorough understanding of the material's photophysics becomes a pressing matter. Since pronounced background doping can easily obscure the actual material properties, it is of paramount importance to understand how different processing conditions affect the observed behavior. Using photoluminescence spectroscopy, thin films of FASnI3 fabricated through different protocols are therefore investigated. It is shown that hot carrier relaxation occurs much faster in highly p‐doped films due to carrier–carrier scattering. From high quality thin films, the longitudinal optical phonon energy and the electron–phonon coupling constant are extracted, which are fundamental to understanding carrier cooling. Importantly, high quality films allow for the observation of a previously unreported state of microsecond lifetime at lower energy in FASnI3, that has important consequences for the discussion of long lived emission in the field of metal halide perovskites. [ABSTRACT FROM AUTHOR]

Hybrid perovskite solar cells have attracted an unprecedented research attention due to their skyrocketing record power conversion efficiency (PCE), which now exceeds 23% in less than a decade from the initial PCE of 3.8%. Besides the excellent optoelectronic properties of the perovskite absorbers, the high efficiencies are also dependent on preparation methods and advanced device engineering. In this study, the role of the device architecture (planar n‐i‐p vs inverted p‐i‐n structure) and of the charge‐selective interlayer on the photophysical properties of the perovskite absorber and device performance are explored. FA0.85MA0.15PbBr0.45I2.55 (MA = methylammonium, FA = formamidinium) as the perovskite absorber and chloride‐capped TiO2 colloidal nanocrystals (TiO2‐Cl) and poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as close‐to‐the‐substrate layers in the conventional and inverted structures are employed, respectively. Extremely different device performances are demonstrated by the two structures. The device where the active layer is deposited on TiO2‐Cl displays a champion PCE of 19.9%, while the one using PEDOT:PSS gives about 15.1% efficiency. The photophysical and electrical investigations indicate that the TiO2‐Cl/perovskite interface has lower number of traps, underlining the importance of interfaces for achieving highly performing perovskite solar cells. This study highlights the importance of device architecture and interfaces in planar hybrid perovskite solar cells on device performance. The device based on the conventional structure gives better power conversion efficiency (PCE) of 19.9% in comparison to the inverted structure with PCE of 15.1%. The extreme difference in performance is due to perovskite film morphology and interface traps. [ABSTRACT FROM AUTHOR]

In article number 1701305, Maria Antonietta Loi and co‐workers show that the electron transport capability of the electron‐extracting layer dominates the temperature dependence of the performance of hybrid perovskite solar cells. The authors further demonstrate efficient hybrid perovskite solar cells over a temperature range from 295 K to 160 K by n‐doping the PCBM electron‐extracting layer or using a fullerene derivative with intrinsically higher electron transport capability. [ABSTRACT FROM AUTHOR]