Improved Electron Transport Research Articles

High-Quality (FA)x(MA)1–xPbI3 for Efficient Perovskite Solar Cells via a Facile Cation-Intermixing Technique

The quality of perovskite light-absorbing materials plays a vital role in the photovoltaic performance of perovskite solar cells. Herein, we present a facile surface engineering technique through post-treating pure MAPbI3 films with formamidinium iodide (FAI) solution, leading to mixed-cation FAxMA1–xPbI3 perovskite with substantial grain dimensions and a compact and uniform morphology. It is noted that the film post-treated with 20 mg·mL–1 FAI solution produces a highly crystalline and stable lattice structure with the features like the decreased defect density, improved electron transport, and long carrier lifetime. The optimized device based on the FAxMA1–xPbI3 obtained from the cation-intermixing technique shows a promising power conversion efficiency of 20.21%, which is even superior than that of the device based on the mixed-cation perovskite from the traditional method without post-treatment (19.08%). Moreover, the device based on the developed method also shows a better stability. These findings p...

Engineered living conductive biofilms as functional materials

Abstract

Improving Electron Transport in a Double-Cable Conjugated Polymer via Parallel Perylenetriimide Design

Double-cable conjugated polymer can be applied to single-component organic solar cells (SCOSCs), which have great potential to improve the stability and to simplify the fabrication procedure compar...

A sensitive electrochemical sensor for bisphenol A on the basis of the AuPd incorporated carboxylic multi-walled carbon nanotubes

A sensitive electrochemical sensor for BPA based on the AuPd incorporated carboxylic multi-walled carbon nanotubes (MWCNT) with synergetic amplified current signal was developed, where MWCNT was used as supporter to improve electron transport and poly (diallyldimethylammonium chloride) (PDDA) was used as dispersant for MWCNT and overcome the intrinsic van der Waals interactions between MWCNT and further increase metal NPs loading. The prepared MWCNT-PDDA-AuPd showed enhanced electrocatalytic performance toward BPA, which is better than those of homologous monometallic counterparts and MWCNT-PDDA though the content of AuPd is really low. The peak currents of BPA increased with BPA concentration in linear range of 0.18–18 μM and the detection limit of 60 nM. The sensor showed high sensitivity, good stability, repeatability and can be used to detect BPA in milk and water samples with good performance, which demonstrate that MWCNTs-PDDA-AuPd nanocomposite may be an attractive material in applications of environmental and food analysis.

Reduced graphene oxide@nitrogen doped carbon with enhanced electrochemical performance in lithium ion batteries

Reduced graphene oxide (rGO) has attracted wide attention as anode materials of lithium ion batteries, however, restacking of rGO sheets limits its capacity and rate performance. To address this issue, a sandwich-like composite of N-doped carbon (NDC) and rGO (rGO@NDC) was fabricated via a process of absorbing [EMIm]N(CN)2 ionic liquid on the surface of graphene oxide (GO) nanosheets and subsequent heat-treating of the composite. The rGO@NDC composite exhibits a high specific capacity of 409.4 mAh g−1 with a Coulombic efficiency of 100% after 50 cycles at a charge-discharge rate of 0.5 C, and a specific capacity of 222.8 mAh g−1 with no capacity fade after 1200 cycles at charge-discharge rate of 10 C. Compositing the rGO with NDC particles can decrease the superficial oxygen-containing functional groups of the rGO, and therefore decrease side reactions during battery cycling. And embedding of NDC particles on the surface of rGO sheets avoids the restacking of rGO sheets and enlarges the interlayer space of the rGO to facilitate Li+ transport within the rGO@NDC. Finally, the NDC particles provide more accessible sites for Li+, and rGO sheets as conductivity networks improves electron transport.

Enhanced Device Performance of Bulk Heterojunction (BHJ) Hybrid Solar Cells Based on Colloidal CdSe Quantum Dots (QDs) via Optimized Hexanoic Acid-Assisted Washing Treatment

As-synthesized colloidal quantum dots (QDs) are usually covered by an organic capping ligand. These ligands provide colloidal stability by preventing QDs agglomeration. However, their inherent electrical insulation properties deliver a problem for hybrid solar cell application, disrupting charge transfer, and electron transport in conjugated polymer/QDs photoactive blends. Therefore, a surface modification of QDs is crucial before QDs are integrated into solar cell fabrication. In this work, enhancement of power conversion efficiency (PCE) in bulk heterojunction (BHJ) hybrid solar cells based on hexadecylamine- (HDA-) capped CdSe quantum dots (QDs) has been achieved via a postsynthetic hexanoic acid washing treatment. The investigation of the surface modification was performed to find the optimum of washing time and their effect on solar cell devices performance. Variation of washing time between 16 and 30 min has been conducted, and an optimum washing time was found at 22 min, resulting in a high PCE of 2.81%. The efficiency enhancement indicates improved electron transport, contributing in an increased short-circuit current density of solar cell devices.

Fabrication of peanut-like TiO2 microarchitecture with enhanced surface light trapping and high specific surface area for high-efficiency dye sensitized solar cells

The quality of TiO2 photoelectrode is critical to fabricate high-performance dye-sensitized solar cells (DSSCs), but constructing TiO2 microstructure with high exposure reactive facets and high specific surface area is still a challenge. Herein, we present a facile route for creating a novel peanut-like (PN) anatase TiO2 microstructure with high exposed (001) facet, enhanced light trapping and large specific surface area using a one-pot hydrothermal method without fluorion assistance. With the introduction of diethylenetriamine as shape controlling agent and two-phase interface by etherification reaction of isopropyl alcohol, anatase PN TiO2 microarchitecture consisted with ultrathin nanosheets can be successfully fabricated. The obtained PN TiO2 combines the advantages of high exposed reactive (001) facets and large specific surface area (180.8 m2/g). The PN TiO2 based DSSC exhibits an outstanding photovoltaic conversion efficiency up to 9.14%, which can attribute to larger dye loading, superior light scattering capability, higher electron collection efficiency, narrower bandgap as well as efficient electron injection, together with improved electron transport and reduced charge recombination due to the unique peanut-like microstructure. Our work demonstrates the potential of PN TiO2 for improving the performance of energy storage devices.

Electron Transport Improvement of Perovskite Solar Cells via a ZIF-8-Derived Porous Carbon Skeleton

To improve electron transport rate of perovskite solar cells, a ZIF-8-derived porous carbon skeleton layer is prepared by carbonizing the ZIF-8 thin film on conducting glass as the electron transport skeleton of a perovskite solar cell. Polyvinylpyrrolidone is added during the synthesis of ZIF-8 to reduce the particle size of ZIF-8 and decrease the carbonization temperature below 600 °C. The porous structure of ZIF-8 is mainly reserved at the optimized carbonization temperature. Then, TiO2 nanoparticles are deposited on the surface of a porous carbon skeleton to form an electron transport layer of a perovskite solar cell with the structure of FTO/ZIF-8-derived porous carbon layer/TiO2/perovskite/spiro-OMeTAD/Au. Because of the good conductivity of the ZIF-8-derived porous carbon skeleton, the photogenerated electron transport rate of the perovskite solar cell is increased. At the same time, the porous structure of the ZIF-8-derived carbon layer increases the contact area between the perovskite layer and t...

Modulating Carrier Transport via Defect Engineering in Solar Water Splitting Devices

Developing sustainable solar water splitting devices requires efficient separation and transport of photogenerated carriers. In this Perspective, we examine carrier transport in semiconductor photoelectrodes using bismuth vanadate as a primary model system and highlight strategies to significantly improve carrier delivery through defect engineering. To improve electron transport in low-mobility semiconductors, we introduce two distinct bulk doping methods, by homogeneously enhancing the bulk defect level or by forming distributed homojunctions with graded doping. Next, we demonstrate the use of structural boundaries as extrinsic pathways for fast electron transport, thus providing novel insights to engineer materials’ macroscopic conductivity. Third, we describe the importance of interface design in terms of structural, chemical, and electronic matching at the back contact to suppress carrier recombination. Finally, we highlight the methods for surface defect control via passivation and catalysis and give...

Electrodeposited p-type Cu2O thin films at high pH for all-oxide solar cells with improved performance

We report the electrodeposition of cuprous oxide (Cu2O) films from cupric sulfate-lactate electrolytes at high pH 13.5 and their performance in all-oxide fluorine-doped tin oxide/Cu2O/aluminium-doped zinc oxide solar cells. The deposit grains are found to grow with rather randomly distributed <111> and <100> crystal orientations and have a poorly-definded morphology with evidence of chemical dissolution that takes place during the deposition process. Significant improvements in the solar cell performance with high power conversion efficiencies of up to 1.55% is achieved, which is much better that those (<0.2%) of solar cells with Cu2O layer electrodeposited at lower pH. The performance enhancement is primarily attributed to the improved electron transport in the Cu2O thin film due to partial merging of grains.

P-N Junction Diode Using Plasma Boron-Doped Black Phosphorus for High-Performance Photovoltaic Devices.

This study used a spatially controlled boron-doping technique that enables a p-n junction diode to be realized within a single 2D black phosphorus (BP) nanosheet for high-performance photovoltaic application. The reliability of the BP surface and state-of-the-art 2D p-n heterostructure's gated junctions was obtained using the controllable pulsed-plasma process technique. Chemical and structural analyses of the boron-doped BP were performed using X-ray photoelectron spectroscopy, transmission electron microscopy, and first-principles density functional theory (DFT) calculations, and the electrical characteristics of a field-effect transistor based on the p-n heterostructure were determined. The incorporated boron generated high electron density at the BP surface. The electron mobility of BP was significantly enhanced to ∼265 cm2/V·s for the top gating mode, indicating greatly improved electron transport behavior. Ultraviolet photoelectron spectroscopy and DFT characterizations revealed the occurrence of significant surface charge transfer in the BP. Moreover, the pulsed-plasma boron-doped BP p-n junction devices exhibited high-efficiency photodetection behavior (rise time: 1.2 ms and responsivity: 11.3 mA/W at Vg = 0 V). This study's findings on the tunable nature of the surface-transfer doping scheme reveal that BP is a promising candidate for optoelectronic devices and advanced complementary logic electronics.

Porous polyaniline/carbon nanotube composite electrode for supercapacitors with outstanding rate capability and cyclic stability

Polyaniline (PANI) is one of the most widely used organic electrode materials for supercapacitors. It has advantages such as good environmental stability and low cost, whereas it is difficult to achieve high capacitance, good rate capability and long cycle life simultaneously. In this work, a series of porous polyaniline/carbon nanotube (PANI/CNT) composite materials are prepared by chemically grafting PANI on CNTs and creating interpenetrating pores via templating using CaCO3 nanoparticles, and then studied as electrode materials for supercapacitors. As PANI is covalently grafted on CNT networks formed in the electrode, the delocalization of electrons improves electron transport in the electrode and the stability of PANI in redox cycling process. The porous morphology created provides sufficient channels for the transport of ions. As a result, the optimized PANI/CNT composite exhibits a high capacitance of 1266 F g−1 at a specific current of 1 A g−1, and even at a specific current of 128 A g−1 the specific capacitance could reach 864 F g−1. Moreover, after cycling tests of 10,000 cycles, it remains 83% of its capacitance at the first cycle. The excellent rate performance and cycle stability of the porous PANI/CNT composite makes it a promising high-performance electrode material for supercapacitors.

Electronic structure of Ba(OH)2 interface in inverted organic photovoltaics: Improved electron transport by charged state of C60

Lowering the work function (WF) of the cathode in inverted organic photovoltaics (OPVs) is critically important to obtaining a high power conversion efficiency (PCE). The insertion of functional interlayers between the cathode and acceptor is a widely employed strategy to lower the WF. Among these functional materials, Ba(OH)2 is known to be an efficient solution-processable cathode buffer layer that improves the electron transport in organic optoelectronic devices. Despite several reports of device performance enhancement with the use of a Ba(OH)2 layer, its interfacial energetics is yet to be clearly understood. In this study, we investigated the electronic structure of Ba(OH)2 interfaces and the improvement in the PCE of inverted small molecule OPVs with the use of a Ba(OH)2 layer. On implementing the optimum thickness of the Ba(OH)2 layer, the PCE of the OPVs was significantly enhanced from 1.29% to 3.41%, and the S-shaped kink in the current-density–voltage curve was eliminated. To elucidate the underlying mechanism of this phenomenon, we explored the interfacial electronic structures of C60/indium tin oxide (ITO) and C60/Ba(OH)2/ITO using in situ photoelectron spectroscopy. The spin-coated Ba(OH)2 was physisorbed onto the ITO, which significantly reduced its WF. Owing to the Ba(OH)2, the reduced WF of the ITO is lower than the electron affinity of C60. Thus, a charge transfer is induced from Ba(OH)2/ITO to C60, and the charged states of C60 are observed within the monolayer. These charged states result in significant band bending in the C60 layer, such that its lowest unoccupied molecular orbital (LUMO) level shifts toward the Fermi level (EF) of the Ba(OH)2/ITO. As a result, the energy offset between the C60 LUMO level and the cathode EF is substantially reduced from 0.45 eV to 0.15 eV with the use of the Ba(OH)2 layer. This is the origin of the enhanced device performance of OPVs.

Valence and conduction band offsets for sputtered AZO and ITO on (010) (Al0.14Ga0.86)2O3

(AlxGa1−x)2O3/Ga2O3 metal-oxide semiconductor field effect transistors are emerging as candidates for rf and power electronics, but a drawback is the high contact resistances on these wide bandgap semiconductors. A potential solution is to use narrower gap transparent conducting oxides such as IZO and ATO to reduce the interfacial resistance. In this paper, we report the measurement of the valence band offset of the AZO/(Al0.14Ga0.86)2O3 and ITO/(Al0.14Ga0.86)2O3 heterointerfaces using x-ray Photoelectron Spectroscopy. The single-crystal β-(Al0.14Ga0.86)2O3 was grown by molecular beam epitaxy. The bandgaps of the sputter-deposited AZO and ITO were determined by reflection electron energy loss spectroscopy to be 3.2 ± 0.20 and 3.5 ± 0.20 eV, respectively, while high resolution XPS data of the O 1s peak and onset of elastic losses was used to establish the (Al0.14Ga0.86)2O3 bandgap as 5.0 ± 0.30 eV. The valence band offsets were −0.59 eV ± 0.10 eV and −1.18 ± 0.20 eV, respectively, for AZO and ITO. The conduction band offsets were 1.21 ± 0.25 eV for AZO, and 0.32 ± 0.05 eV for ITO. Both were of the straddling gap, type I alignment on β-(Al0.14Ga0.86)2O3 and all the offsets are negative, consistent with achieving improved electron transport across the heterointerface.

Electronically-Coupled Phase Boundaries in α-Fe2O3/Fe3O4 Nanocomposite Photoanodes for Enhanced Water Oxidation

Photoelectrochemical (PEC) water splitting reactions are promising for sustainable hydrogen production from renewable sources. We report here, the preparation of α-Fe2O3/Fe3O4 composite films via a single-step chemical vapor deposition of [Fe(OtBu)3]2 and their use as efficient photoanode materials in PEC setups. Film thickness and phase segregation was controlled by varying the deposition time and corroborated through cross-section Raman spectroscopy and scanning electron microscopy. The highest water oxidation activity (0.48 mA/cm2 at 1.23 V vs RHE) using intermittent AM 1.5 G (100 mW/cm2) standard illumination was found for hybrid films with a thickness of 11 μm. This phenomenon is attributed to an improved electron transport resulting from a higher magnetite content toward the substrate interface and an increased light absorption due to the hematite layer mainly located at the top surface of the film. The observed high efficiency of α-Fe2O3/Fe3O4 nanocomposite photoanodes is attributed to the close pr...

Optimization of the doping process and light scattering in CdS:Mn quantum dots sensitized solar cells for the efficiency enhancement

In this work a double-layer photoanode composed of TiO2 nanocrystals (NCs) and hollow spheres (HSs) was applied in CdS:Mn sensitized solar cells. TiO2 NCs with dominant size of 25 nm were synthesized by a facile hydrothermal method. TiO2 HSs were also prepared through the liquid phase deposition (LPD) of TiO2 on carbon spheres followed by a calcination process. The double electron transport layer of quantum dot sensitized solar cells (QDSCs) was formed of a nanocrystalline TiO2 layer covered by a light scattering HSs film. The corresponding thicknesses were also controlled to be about 10 µm and 7 µm, respectively. The sensitization of photoanode with Mn doped CdS NCs were carried out by a successive ionic layer adsorption and reaction (SILAR) technique. The apparent $$\frac{\text{Mn}}{\text{Mn}+\text{Cd}}$$ molar ratio was altered in a wide range of 0–9%. The corresponding QDSCs were fabricated and the doping process was optimized for the improved power conversion efficiencies. According to the results, the QDSC with a double-layer photoanode sensitized with $$\frac{\text{Mn}}{\text{Mn}+\text{Cd}}$$ ratio of 7.0% showed the maximum efficiency of 3.26%. This value was increased about 61% and 18% compared to those of the reference cells with single nanocrystalline and double-layer photoanodes sensitized with un-doped CdS NCs. The reason was addressed due to the higher light scattering and Mn related electron energy states within the bandgap energy of CdS NCs and the improved electron transport property of the cell. A ZnS passivating layer was also utilized as the electron blocking layer on the surface of the optimized doped photoanode with different thicknesses. It was shown that the highest energy conversion efficiency of 3.55% was achieved for three cycles of ZnS SILAR deposition.

Effect of TiO2-rGO heterojunction on electron collection efficiency and mechanical properties of fiber-shaped dye-sensitized solar cells

It is demonstrated that the incorporation of graphene materials into oxide-based photoanodes can greatly increase the photoelectrochemical devices’ performances. In this work, reduced graphene oxide (rGO) has been incorporated into P25-TiO2 nanoparticle (NP) based photoanodes for fiber-shaped dye-sensitized solar cells (FDSSCs). Results showed that the rGO nanosheets have been uniformly dispersed within P25 nanoparticle layers, and, as expected, the incorporation of rGO increased the FDSSCs’ short current density from 8.344 to 12.935 mA cm−2, open circuit voltage from 0.775 to 0.798 V, resulting into their power conversion efficiency (PCE) from 3.940% to 5.364%. This large increasement in PCE could be due to two aspects, i.e. the improved electron transport properties via rGO and the enhanced separation of photogenerated hole–electron pairs via rGO-TiO2 heterojunction. Furthermore, the incorporation of rGO can also make the FDSSCs have good mechanical properties, which is very crucial for their future applications in smart wearable electronics. In addition, based on our analysis, a possible rGO/multi-NP coupling enhancement mechanism was proposed.

A colloidal heterostructured quantum dot sensitized carbon nanotube-TiO2 hybrid photoanode for high efficiency hydrogen generation.

Solar-driven photoelectrochemical (PEC) hydrogen (H2) generation is a promising approach to harvest solar energy for the production of a clean chemical fuel. However, the low photon-to-fuel conversion efficiency and long-term stability of PEC devices are major challenges to be addressed to enable large-scale commercialization. Here we report a simple, fast and cost-effective approach to fabricate high efficiency and stable PEC devices for H2 generation, by fabricating a hybrid photoanode obtained by incorporating small amounts of multiwall carbon nanotubes (MWCNTs) into a TiO2 mesoporous film and sensitizing with colloidal heterostructured CdSe/(CdSexS1-x)5/(CdS)2 quantum dots (QDs). The latter were specially designed to accelerate the exciton separation through a band engineering approach. The PEC devices based on the TiO2/QD-MWCNT (T/Q-M) hybrid photoanode with an optimized amount of MWCNTs (0.015 wt%) yield a saturated photocurrent density of 15.90 mA cm-2 (at 1.0 VRHE) under one sun illumination (AM 1.5G, 100 mW cm-2), which is 40% higher than that of the reference device based on TiO2/QD (T/Q) photoanodes. This is attributed to a synergistic effect of the promising optoelectronic properties of the colloidal heterostructured QDs and improved electron transport (reduced charge transfer resistance) within the TiO2-MWCNT hybrid anodes enabled by the directional path of MWCNTs for the photo-injected electrons towards FTO. Furthermore, the PEC device based on the T/Q-M hybrid photoanode is more stable (∼19% loss of its initial photocurrent density) when compared with the T/Q photoanode (∼35% loss) after two hours of continuous one sun illumination. Our results provide fundamental insights and a different approach to improve the efficiency and long-term stability of PEC devices and represent an essential step towards the commercialization of this emerging solar-to-fuel conversion technology.

Highly efficient polymer solar cells based on low-temperature processed ZnO: application of a bifunctional Au@CNTs nanocomposite

Incorporating Au@CNTs nanocomposite into low-temperature ZnO electron transport layers to suppress the destructive trap states and improve electron transport properties.

Constructing Heterointerface of Metal Atomic Layer and Amorphous Anode Material for High-Capacity and Fast Lithium Storage.

Interfacial engineering plays an important role in tuning the intrinsic property of electrode materials for energy applications such as lithium-ion batteries (LIBs), which however is rarely realized to amorphous electrode materials, despite a set of characteristics of amorphous materials desirable for LIBs. Here, Au atomic cluster layer-interfaced amorphous porous CoSnO3 nanocubes were fabricated by galvanic replacement and employed as a superior LIB anode, showing high reversible capacity (1615 mAh g-1 at 0.2 A g-1), good rate capability (1059 mAh g-1 with a 61.3% capacity retention upon the dramatic current variation from 0.1 to 5 A g-1), and excellent cycling stability. The amorphous nature, interconnected mesopores, and especially the thin Au atomic cluster layer on the surface/pore walls of CoSnO3 nanocubes can not only improve electron transport and ion diffusion in the electrode and electrolyte but also release the volume strain. Most significantly, density functional theory calculations reveal that the CoSnO3∥Au heterointerface can induce the atomic polarization of CoSnO3 and lower Li ion diffusion barriers in CoSnO3 near the heterointerface, endowing it with a significantly enhanced theoretical lithium storage capacity and outstanding rate capability. This study provides a model of a heterointerface for amorphous materials with desired properties for high-performance LIBs and future energy applications.