Electron Collection Efficiency Research Articles

Bifunctional SnO2 Colloid Offers No Annealing Effect Compact Layer and Mesoporous Scaffold for Efficient Perovskite Solar Cells

AbstractSnO2 compact layer (c‐SnO2) frequently suffers from degradation in high temperature processes (HTP) such as crack, worse interfacial contact, and electrical properties, that is, annealing effect. To solve this problem, a kind of bifunctional SnO2 colloid is developed by using small molecular oxalate whose organic components can be removed clearly at a low temperature process (LTP). The c‐SnO2 and SnO2 mesoporous layer (m‐SnO2) derived from the fresh and aged sols with the same colloid show no annealing effect, decreasing oxygen vacancy, and adsorbing water on increasing annealing temperature. The champion devices of LTP and HTP SnO2 planar perovskite solar cells (PSCs) achieve, respectively, stabilized photoelectric conversion efficiencies (PCEs) of 20.74% and 20.70%. In contrast, the performance of champion devices of their mesoporous counterparts is significantly improved, showing nearly hysteresis free character with stabilized PCEs of 22.40% and 22.37%, respectively. The inclusion of m‐SnO2 plays a role of an energy bridge, improving electrons collection efficiency, which is supported by photoluminescence and transient photoluminescence characterizations. HTP SnO2 mesoporous PSCs can preserve 97.6% and 80% of their initial PCEs after aging for 25 weeks and 8‐h irradiated/16‐h dark cycle within 104 h. The high stability of HTP SnO2 PSCs may ascribe to low oxygen vacancy and adsorbed water of HTP SnO2.

Assembly of Cu–In–Sn–Se quantum dot–sensitized TiO2 films for efficient quantum dot–sensitized solar cell application

Ternary I-III-VI (such as CuInSe2 and AgInS2) quantum dots (QDs) have been increasingly studied in the field of photoelectric conversion applications. Here, we prepare a relatively less toxic Cu–In–Sn–Se (CISSe) QD by an organic high-temperature hot injection method, and this material is subsequently applied as a functional sensitizer to produce QD-sensitized solar cells (QDSSCs). Because of the effect of Sn doping and ZnS passivation, the TiO2/CISSe/ZnS photoanode obtains the greatest composite resistance (985.5 Ω·cm2) and highest electron lifetime (120.23 ms) among the experimentally compared materials, showing the further inhibition of charge recombination when compared with bare Cu–In–Se solar cells while effectively enhancing the collection efficiency of photogenerated electrons. Using CISSe/ZnS QDs as a sensitizer, the power conversion efficiency of the QDSSC reaches 6.7%, of which Voc, Jsc, and FF reach 0.559 V, 22.93 mA/cm2, and 0.52, respectively. It provides a new possibility for the development of QDSSCs.

Development of interlayers based on polymethacrylate incorporating tertiary amine for organic solar cells with improved efficiency and stability

Nonfullerene acceptors have played a critical role in achieving record efficiency of organic photovoltaic (OPV) devices, and ITIC-based materials are an important type of nonfullerene acceptor. Herein, we developed new interlayer polymers for nonfullerene acceptor-based OPVs: PDMA(N)EMA and PDMA (N–O)EMA. In particular, PDMA(N)EMA effectively lowered the work function at the interface with the bulk heterojunction active layer and thus enabled efficient electron collection by the OPV device. Therefore, the OPV device incorporating PDMA(N)EMA showed a power conversion efficiency (PCE) of 8.19%, which was substantially enhanced compared with the 4.54% PCE of an ethoxylated polyethylenimine (PEIE)-based device. Whereas PEIE chemically attacked ITIC and degraded the performance of the OPV device, the PDMA(N)EMA formed a stable interface with ITIC, resulting in a dramatic increase of the VOC of the PDMA(N)EMA-based devices. Furthermore, the suppression of degradation at the PDMA(N)EMA interface also improved device stability at elevated temperatures. This work highlights the importance of the design and development of appropriate interlayer materials for realizing stable and high-efficiency nonfullerene-based OPVs.

Hybrid Inorganic–Organic Inverted Solar Cells With ZnO/ZnMgO Barrier Layer and Effective Organic Active Layer for Low Leakage Current, Enhanced Efficiency, and Reliability

This article reports fabrication and characterization of an Inverted inorganic-organic hybrid solar cell based on ITO/(ZnO/ZnMgO)/ZnONR/PCBM/P3HT:PCBM/PEDOT:PSS/Ca-Al heterostructure. Four different cells were fabricated with and without the presence of both the ZnO/ZnMgO barrier layer and ZnO nanorod (NR) structures. The oxide layers were grown on indium tin oxide (ITO) coated glass substrates through the following approaches: i) ZnO layer by radio frequency (RF) sputtering, ii) ZnMgO layer by pulsed laser deposition technique, and iii) ZnO NR by hydrothermal method. Compared to conventional only ZnO based solar cells, incorporation of ZnO/ZnMgO layer as the barrier layer resulted in low leakage current that enormously improved the cell performance. The binary metal oxide layer offers a chemical barrier that protects the ITO layer and leads to better electron collection. Incorporation of a thick (~300 nm) P3HT:PCBM layer (instead of conventional and thin (~100 nm) P3HT coating) between the ZnO/ZnMgO and PEDOT:PSS layers improves electron collection efficiencies. Improvement in short circuit current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ) was observed from 9.5 to 12.3 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A significant increase in external quantum efficiency was also observed. Both J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> and fill factor were found to be improved simultaneously owing to suitable shunt and series resistance attributes. Furthermore, the presence of the thin ZnMgO layer between P3HT:PCBM and dense ZnO layer suppresses the impact of oxygen vacancies, which in turn improves the charge carrier mobility and lowers leakage current. The fabricated cell showed a power conversion efficiency of ~4.95%. Reliability study for 1400 h indicates that the device outperforms the conventional ZnO-based inverted organic solar cells.

Power Conversion Efficiency Improvement of Planar Organic Photovoltaic Cells Using an Original Hybrid Electron-Transporting Layer.

In organic photovoltaic (OPV) cells, besides the organic active layer, the electron-transporting layer (ETL) has a primordial role in transporting electrons and blocking holes. In planar heterojunction-OPVs (PHJ-OPVs), the ETL is called the exciton blocking layer (EBL). The optimum thickness of the EBL is 9 nm. However, in the case of inverted OPVs, such thickness is too high to permit efficient electron collection, due to the fact that there is no possibility of metal diffusion in the EBL during the top metal electrode deposition. In the present work, we show that the introduction of a thin potassium layer between the indium tin oxide (ITO) cathode and the EBL increases dramatically the conductivity of the EBL. We demonstrate that K not only behaves as a simple ultrathin layer allowing for the discrimination of the charge carriers at the cathode/organic material interface but also by diffusing into the EBL, it increases its conductivity by 3 orders of magnitude, which allows us to improve the shape of the J–V characteristics and the PHJ-inverted OPV efficiency by more than 33%. Moreover, we also show that PHJ-inverted OPVs with K in their EBLs are more stable than those with Alq3 alone.

Charge Transporting Materials Grown by Atomic Layer Deposition in Perovskite Solar Cells

Charge transporting materials (CTMs) in perovskite solar cells (PSCs) have played an important role in improving the stability by replacing the liquid electrolyte with solid state electron or hole conductors and enhancing the photovoltaic efficiency by the efficient electron collection. Many organic and inorganic materials for charge transporting in PSCs have been studied and applied to increase the charge extraction, transport and collection, such as Spiro-OMeTAD for hole transporting material (HTM), TiO2 for electron transporting material (ETM) and MoOX for HTM etc. However, recently inorganic CTMs are used to replace the disadvantages of organic materials in PSCs such as, the long-term operational instability, low charge mobility. Especially, atomic layer deposition (ALD) has many advantages in obtaining the conformal, dense and virtually pinhole-free layers. Here, we review ALD inorganic CTMs and their function in PSCs in view of the stability and contribution to enhancing the efficiency of photovoltaics.

Plasmonic silver sandwich structured photoanode and reflective counter electrode enhancing power conversion efficiency of dye-sensitized solar cell

This work describes the efficient improvement of dye-sensitized solar cells (DSSC) utilizing a photoanode with a plasmonic sandwiched silicon dioxide/silver/titanium dioxide (SiO2/Ag/TiO2) structure and a counter electrode (CE) of polypyrrole/reduced graphene oxide/indium tin oxide (Ppy/rGO/ITO) assembled with an aluminium (Al) foil as a reflective layer. The localized surface plasmonic resonance induced from Ag increases the absorption of the dye molecules, and hence significantly improves the electron collection and light-harvesting efficiencies. Compared with conventional photoanode of DCCSs composed of TiO2 paste, the photovoltaic cells containing the plasmonic sandwiched structure exhibits a remarkable improvement in the power conversion efficiency (ƞ), with up to a 2-fold enhancement (from 0.6% to 1.2%), along with a 68.37% increment in the short-circuit current density (Jsc), from 2.15 to 3.62 mA cm−2. The reflective layer of Al foil contributes to a significant enhancement of ƞ of 1.7-fold for the DSSC.

High-efficient ultraviolet (UV) photocathode using optimum radial shaped AlxGa1-xN nanostructure with assisted external electric field

Abstract In this paper, we study the influence of the distribution of Al composition, the built-in electric field and the height of the sublayer on the optical and electrical response of the gradient Al composition AlxGa1-xN photocathode. The results show that the electrical response of these nanoarrays mainly depends on the technical parameters such as the structure spacing, incident light angle and distribution of Al composition. In this work, using the spicer three-step emission theoretical model, we systematically analyzed the quantum efficiency and collection efficiency of gradient Al composition AlxGa1-xN nanostructure with different Al composition distributions. Surprisingly, when the photon energy is 4.4eV~6eV and the Al composition is 0 and 0.635, AlxGa1-xN nanostructures with sublayer heights of 300 nm and 200 nm reach optimized quantum efficiency. Taking into account the diffusion movement of the emitted electrons and the re-absorption effect of the sub-wavelength surface, we introduced the assisted external electric field to improve the collection efficiency of the photocathode. When the external electric field is 2.5 V/μm, the spacing is 300 nm and the incident angle is 30°, the variable Al composition nanostructure can achieve an electron collection efficiency of nearly 31.13%. The research methods and results in this paper provide an optimized solution with reference value for the next generation of high-performance UV photodetectors using gradient Al composition AlxGa1-xN nanostructures to improve photoelectric properties of the photocathode.

Interpretation of effective gain variations with the drift electric field for a ceramic thick gas electron multiplier

The effective gain variations as a function of the drift electric field strength (Ed) are measured in a ceramic thick gas electron multiplier (THGEM) and a standard GEM using the same experimental setup. Significant differences in the variations are observed between the THGEM and the standard GEM. The effective gain variations with Ed are quantitatively reproduced by calculations via investigating the respective influence of Ed change on the electron collection efficiency and the gain. The differences in the effective gain variation with Ed between the THGEM and standard GEM are thus explained.

The Importance of Schottky Barrier Height in Plasmonically Enhanced Hot‐Electron Devices

AbstractPlasmonically enhanced hot‐electron (PEH) photodiodes are a new class of optoelectronic device with the potential to be selective to spectral position, polarization, and bandwidth. Reported solid‐state PEH devices based on metal nanoparticles generally have low performance, in part, due to low collection efficiency of photogenerated hot electrons. A correlation is found between the measured external quantum efficiency (EQE) and the temperature at which the ALD‐TiO2 is deposited by atomic layer deposition (ALD) in Au–TiO2‐based PEH photodiodes. By investigating the material properties of the TiO2, it is demonstrated that the change in EQE is driven by a change in the energy levels in the semiconductor. The results show that lowering the implied Schottky barrier height increases the collection efficiency of hot electrons over the junction, in agreement with existing analytical models. This work demonstrates the crucial role that barrier height plays in hot electron devices in general, and indicates that this is an important design consideration for the improvement of PEH photodetectors.

Improved Photoelectrochemical Performances of Aqueous Mesoscopic Solar Cells

Conventional mesoscopic dye-sensitized solar cells using organic solvents based electrolytes generally have the disadvantages of high vapour pressure against reliable encapsulation, and most importantly, are not environmentally friendly. Aqueous electrolytes based on water possess advantages such as low-cost, earth-abundant, non-toxic and non-flammable, therefore, attracted considerable research interests. However, aqueous electrolyte would negatively shift the conduction band of TiO2 as the water molecules irreversibly change the interfacial properties of the sensitized TiO2 film. Tungsten doped (W-doped) TiO2 mesoporous nanoparticle aggregates, possessing high surface area and superior scattering effect, were used for photoanode preparation. The W-doping would induce a positive shift of the TiO2 conduction band, and enhance the driving force for electron injection and collection efficiencies. The electrochemical impedance spectra indicated a retarded charge recombination and increased electron diffusion length after W-doping. Aqueous DSCs produced a significant improved the open circuit voltage of 712 mV and a short circuit current of 7.05 mA·cm-2, leading to an overall increased power conversion efficiency of 3.40% at 1 sun, a nearly 25% enhancement compared to the non-doped photoanode.

Enhanced photoelectrochemical performance of Bi2S3/Ag2S/ZnO novel ternary heterostructure nanorods

The current work investigates the morphology, crystallinity and photoelectrochemical (PEC) performance of bismuth sulfide/silver sulfide/zinc oxide nanorods (Bi2S3/Ag2S/ZnO NRAs) photoelectrodes as prepared at different annealing temperature. ZnO NRAs was initially grown hydrothermally, deposited in sequence with Ag2S and Bi2S3 via successive ionic layer adsorption and reaction (SILAR) method before undergoing the annealing treatment. The optimised photoelectrode (Bi2S3/Ag2S/ZnO NRAs-400 °C) possesses an optical bandgap of 1.60 eV extending the absorption edge of ZnO to visible light spectrum. The current-voltage characterization of Bi2S3/Ag2S/ZnO NRAs photoelectrodes revealed that the photocurrent density and photoconversion efficiency were strongly dependent on the annealing temperature. The PEC study shows that the photoelectrode annealed at 400 °C achieved impressive photocurrent density of 12.95 mA/cm2 at +0.5 V (vs Ag/AgCl/saturated KCl) under 100 mW/cm2 illumination with superior photoconversion efficiency of 12.63%. This improvement is due to the cascade-designed band structure alignment of Bi2S3/Ag2S/ZnO/ITO and to the brilliant role of Ag2S as an intermediate layer that reduced random chance of electron-hole (e−-h+) pairs recombination and improved the electrons collection efficiency. This work is highly anticipated to give contribution on further utilisation of Bi2S3/Ag2S/ZnO NRAs as a promising semiconductor material in PEC related applications.

Compact Titania Films by Spray Pyrolysis for Application as ETL in Perovskite Solar Cells

Hybrid perovskite-based solar cells are projected as a potentially viable photovoltaic (PV) technology for large-scale implementation. The electron transport layer (ETL) should be dense and pinhole-free to facilitate efficient electron collection and transport from the perovskite layer to the anode, which is very important for achieving high-performance solar cells. In this study, a compact TiO2 layer was synthesized by a scalable spray pyrolysis technique. The effect of deposition temperature on the transparency, microstructure, and bandgap of c-TiO2 film was studied. Pinhole-free nanocrystalline films having > 85% transparency with uniform coverage was obtained on spray pyrolysis at 400°C and annealing at 450°C. Usability of the deposited films as ETL in perovskite solar cells was tested by fabricating solar cells (FTO/c-TiO2/FA0.85MA0.15Pb(I0.85Br0.15)3/CuSCN/Au) using the deposited films and comparing their performance. Cell efficiency close to 11.75% with a fill factor of 69% was obtained in the cell fabricated using the films deposited at 400°C.

Polyethylenimine-Ethoxylated Interfacial Layer for Efficient Electron Collection in SnO2-Based Inverted Organic Solar Cells

In this work, we studied inverted organic solar cells based on bulk heterojunction using poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C71-butyric acid methyl ester (P3HT:PCBM) as an active layer and a novel cathode buffer bilayer consisting of tin dioxide (SnO2) combined with polyethylenimine-ethoxylated (PEIE) to overcome the limitations of the single cathode buffer layer. The combination of SnO2 with PEIE is a promising approach that improves the charge carrier collection and reduces the recombination. The efficient device, which is prepared with a cathode buffer bilayer of 20 nm SnO2 combined with 10 nm PEIE, achieved Jsc = 7.86 mA/cm2, Voc = 574 mV and PCE = 2.84%. The obtained results exceed the performances of reference solar cell using only a single cathode layer of either SnO2 or PEIE.

Dye-sensitized titanium dioxide nanotube array solar cells with superior performance induced by ferroelectric barium titanate

Here we have coupled ferroelectric barium titanate (BaTiO3) with titanium dioxide (TiO2) nanotubes to improve performance of dye-sensitized solar cells with the aid of ferroelectric polarization. Measurements with the use of UV–vis spectroscopy reveal that BaTiO3 modified TiO2 nanotubes electrode shows more dye adsorption and greater fraction of light scattering. Moreover, the electron transport and recombination dynamics via electrochemical impedance spectroscopy and intensity modulated photocurrent/photovoltage spectroscopy measurements reveals that BaTiO3 modified TiO2 nanotubes cell has a faster electron transport, slower electron recombination and higher electron collection efficiency than original TiO2 nanotubes cell. The ferroelectric BaTiO3 modified TiO2 nanotubes cell exhibits a power conversion efficiency of 10.15%, which is higher than that of original TiO2 nanotubes cell (9.30%).

Carbon/binder free 3D Si@Cu2O anode for high performance lithium ion battery

A liquid-phase reduction method was applied to the synthesis of Cu2O microspheres as a 3D array current collector. An active silicon film with a tunable thickness was then deposited on the 3D Cu2O microspheres by magnetic sputtering as the carbon/binder free anode for lithium ion battery (LIB). As a comparison, Si-Cu2O composite electrode was also prepared via a solvothermal method. The specific capacity of Si@Cu2O-15 anode gradually decreased from 1596.8 mA h.g–1 to 1526.9 mA h▪g–1 after 100 cycles with an average loss of specific capacity at 0.24% per cycle. Moreover, the coulomb efficiency of the electrode remained at about 98%. Furthermore, the reversible capacity of the Si@Cu2O-15 anode still maintained above 709.0 mA h.g–1 after 60 cycles at a higher rate of 2 C, being ascribed to the improved diffusion rate of charge at the solid-liquid interface and to the collection efficiency of electrons in the 3D current collector, which was higher than that of Si-Cu2O composite anode (remained as 448 mA h.g–1 after 60 cycles at 2 C).

Development of a retarding-field type magnetic bottle spectrometer for studying the internal-conversion process of [formula omitted

The nuclear half-life of 235mU (the first metastable nuclear excited state of235U) varies depending on chemical environments because the nucleus interacts only with outer-shell electrons in the nuclear internal conversion (IC) process due to its extremely low excitation energy at 76.737 ± 0.018 eV. Elucidating the mechanism of the half-life variation of this unique isomer would largely contribute to understanding interactions between nuclei and shell electrons. For elucidating the mechanism, we aim at measuring both half-lives and IC electron energy spectra of 235mU in various chemical environments. In this study, we developed a retarding-field type magnetic bottle spectrometer for measuring the half-lives and energy spectra with high signal to noise ratio (S∕N) and high energy resolution. As an evaluation of the fabricated apparatus, the collection efficiency of electrons emitted from a 235mU sample to a channeltron electron detector was measured as a function of the strong and weak magnetic fields and the collection voltage applied to a mesh placed on the entrance of the channeltron detector. Electron collection efficiencies of almost 100% were confirmed under several conditions. Due to this high efficiency together with the low dark noise of the channeltron detector, high S∕N measurements have been achieved successfully. An IC-electron energy spectrum of 235mU recorded under the most efficient condition showed an energy resolution (ΔE∕E) of ∼2%, which is sufficiently high to observe small peak shifts and splittings in the IC-electron energy spectra of 235mU compounds. This developed apparatus allows high precision measurements of half-lives and IC-electron energy spectra of 235mU in various chemical environments even with small amount of 235mU and low emission rate of IC electrons.

Simulation of the Electrostatic Distribution in the Proximity Focusing Structure of an EBCMOS

The electrostatic distribution of an electron bombarded CMOS (EBCMOS) was simulated by Ansoft Maxwell 3D software. Specifically, we studied how the electrostatic distribution was affected by the structure of a back-side bombarded CMOS (BSB-CMOS) and the anode position in electron-bombarded sensors. The simulation results reveal that the electrostatic field may cause a fault in the signal readout of the BSB-CMOS when the anode is positioned under the BSB-CMOS. In contrast, we found that the structure of an EBCMOS will aid electron focusing when the anode is positioned above the BSB-CMOS and the doping concentration of the electron multiplier layer is high. However, the high doping concentration of the electron multiplier layer will reduce the electron collection efficiency due to its rapid electron-hole recombination. We then designed a structure in which the multiplier layer has an overlying ultra-thin highly-doped layer, with an electrostatic distribution that functions to focus electrons. At the same time, this configuration can effectively prevent most of the multiplier electrons from recombining because ultra-thin highly-doped layer is much thinner than incident depth for the high-energy electron. This simulation study will provide a theoretical foundation for the fabrication of high-performance EBCMOS devices. Graphic abstract: a) EBCMOS physical model in Ansoft Maxwell 3D; b) The distribution of electrostatic distribution for BSB-CMOS with an ultra-thin heavily-doped layer. Electrostatic distribution of EBCMOS with different configurations were simulated. The results reveal that the electrostatic field may cause an erroneous readout of the BSB-CMOS if the anode is positioned under the BSB-CMOS. If the high voltage anode is positioned above the CMOS sensor, this is improved, especially when an ultrathin highly-doped multiplier layer is added to improve electron collection efficiency. This study provides a theoretical foundation for the fabrication of high performance EBCMOS devices.

Development of the TIP-HOLE gas avalanche structure for nuclear physics/astrophysics applications with radioactive isotope beams: preliminary results.

We discuss the operational principle and performance of new micro-pattern gaseous detectors based on the multi-layer Thick Gaseous Electron Multiplier (M-THGEM) concept coupled to a needle-like anode. The new gas avalanche structure aims at high-gain operation in nuclear physics and nuclear astrophysics applications with radioactive isotope beams. It is thereafter named TIP-HOLE gas amplifier, and consists of a THGEM or a two-layers M-THGEM mounted in a WELL configuration. The avalanche electrodes are collected by thin conductive needles (with up to a few ten μm radius and a height of 100 μm), located at the center of the hole and acting as a point-like anode. The bottom area of the needle could be surrounded by a cylindrical cathode strip in order to increase the electron collection efficiency. The electric field lines from the drift region above the M-THGEM are focused into the holes, and then forced to converge on the needle tip. An extremely high field is reached at the top of the needle, creating a point-like avalanche process. Stable, high-gain operations in a wide range of pressures can be achieved at relatively low operational voltage, even in pure quencher gas at atmospheric pressure (e.g. pure isobutene). The TIP-HOLE structure may be produced by the innovative scalable additive manufacturing technology for large-area, multiple-layer printed circuit boards, recently developed by the UHV technology company (USA) and discussed for the first time in this work.

Enhanced Charge Carrier Lifetime of TiS3 Photoanode by Introduction of S22− Vacancies for Efficient Photoelectrochemical Hydrogen Evolution

AbstractRecent advances in layered TiS3 has shown appealing potential for photoelectrochemical hydrogen evolution due to its excellent optical and electronic properties. Here, an excellent photoanode, composed of TiS3 nanoribbon arrays with moderate S22− vacancies, is proposed to achieve efficient photoelectrochemical hydrogen evolution. These unique S22− vacancies are introduced in the TiS3 photoanode by a simple vacuum re‐annealing method, which is inspired by crystal structure analyses of TiS3 and TiS2. The existing S22− vacancies are revealed to significantly promote the electron conductivity, charge separation, and transport of the photoanode simultaneously. The resulting TiS3−x photoanode with ≈22% S22− vacancies exhibits a twofold increase in the electron diffusion length for efficient electron collection and a remarkably high photocurrent density of 15.35 mA cm−2 at 1.4 V versus reversible hydrogen electrode.