Suppressing Charge Recombination in ZnO-Nanorod-Based Perovskite Solar Cells with Atomic-Layer-Deposition TiO2

ZnO nanorods are passivated with a TiO2 interracial layer and applied in the CH3NH3PbI3 perovskite solar cell, which prepared by the atomic layer deposition method show a positive effect on the tiff factor and power conversion efficiency. With TiO2 interracial passivation, the charge recombination in the ZnO/CH3NH3PbI3 interface is effectively suppressed and the maximum power conversion efficiency is enhanced from 11.9% to 13.4%.

Photovoltaic Performance and Charge Recombination Dynamics of P3HT/PCBM Blend Heterojunction

We prepared the polymer solar cell based on poly（3-hexylthiophene）（P3HT）/fullerene derivative PCBM（PCBM=[6,6]-phenyl-C61-butyric acid methyl ester） heterojunction and investigated the irradiation intensi- ty-dependent charge recombination dynamics of heterojunction employing nanosecond transient absorption spectroscopy with bias light so as to simulate the photophysical process in heterojunction when the photovoltaic device is on operation. The experimental data exhibit that the yield of free charges gradually decreases and the loss of mobile carriers originated from bimolecular recombination simultaneously increases as the irradiation intensity gradually enhances. This indicates that the polymer solar cell is much suitably used at a low irradiation intensity.

Profile Measurement of Ion Temperature and Toroidal Rotation Velocity with Charge Exchange Recombination Spectroscopy Diagnostics in the HL-2A Tokamak

This paper deals with the profile measurement of impurity ion temperature and toroidal rotation velocity that can be achieved by using the charge exchange recombination spectrum （CXRS） diagnostics tool built on the HL-2A toknmak. By using CXRS, an accurate impurity ion temperature and toroidal plasma rotation velocity profile can be achieved under the condition of neutrM beam injection （NBI） heating. Considering the edge effect of the line of CVI 529.06 nm （n= 8-7）, which contains three lines （active exciting spectral line （ACX）, passivity exciting spectral line （PCX） and electron exciting spectral line （ICE））, and using three Gaussian fitted curves, we obtain the following experimental results： the core ion temperature of HL-2A device is nearly thousands of eV, and the plasma rotation velocity reaches about 104 m· s^-1. At the end of paper, some explanations are presented for the relationship between the curves and the inner physical mechanism.

Charge Exchange Recombination Spectroscopy Based on Diagnostic Neutral Beam in HT-7 Tokamak

Charge exchange recombination spectroscopy （CXRS） based on a diagnostic neutral beam （DNB） installed in the HT-7 tokamak is introduced. DNB can provide a 6 A extracted current at 50 kV for 0.1 s in hydrogen. It can penetrate into the core plasma in HT-7. The CXRS system is designed to observe charge exchange （CX） transitions in the visible spectrum. CX light from the beam is focused onto 10 optical fibers, which view the plasma from -5 cm to 20 cm. The CXRS system can measure the ion temperature as low as 0.1 keV. With CXRS, the local ion temperature profile in HT-7 was obtained for the first time.

Modification to poloidal charge exchange recombination spectroscopy measurement in JT-60U tokamak

With consideration of the effects of the atomic process and the sight line direction on the charge exchange re-combination spectroscopy （CXRS）, a code used to modify the poloidal CXRS measurement on Tokamak-60 Upgrade （JT-60U） in Japan Atomic Energy Research Institute is developed, offering an effective tool to modify the measurement and analyse experimental results further. The results show that the poloidal velocity of ion is overestimated but the ion temperature is underestimated by the poloidal CXRS measurement, and they also indicate that the effect of observation angle on rotation velocity is a dominant one in a core region （r/a 〈 0.65）, whereas in an edge region where the sight line is nearly normal to the neutral beam, the observation angle effect is very small. The difference between the modified velocity and the neoclassical velocity is not larger than the error in measurement. The difference inside the internal transport barrier （ITB） region is 2-3 times larger than that outside the ITB region, and it increases when the effect of excited components in neutral beam is taken into account. The radial electric field profile is affected greatly by the poloidal rotation term, which possibly indicates the correlation between the poloidal rotation and the transport barrier formation.

Ultrafast Terahertz Probes of Charge Transfer and Recombination Pathway of CH_3NH_3PbI_3 Perovskites

We use transient terahertz photoconductivity measurements to demonstrate that upon optical excitation of CH_3NH_3PbI_3 perovskite, the hole transfer from CH_3NH_3PbI_3 into the organic hole-transporting material（HTM）Spiro-OMe TAD occurs on a sub-picosecond timescale. Second-order recombination is the dominant decay pathway at higher photo-excitation fluences as observed in neat CH_3NH_3PbI_3 films. In contrast, under similar experimental conditions, second-order recombination weakly contributes the relatively slow recombination between the electrons in the perovskite and the injected holes in HTM, as a loss mechanism at the CH_3NH_3PbI_3/Spiro-OMe TAD interface. Our results offer insights into the intrinsic photophysics of CH_3NH_3PbI_3-based perovskites with direct implications for photovoltaic devices and optoelectronic applications.

Benzotriazole derivative inhibits nonradiative recombination and improves the UV-stability of inverted MAPbI_(3) perovskite solar cells

Suppressing the nonradiative recombination in the bulk and surface of perovskite film is highly desired to improve the power conversion efficiency(PCE)and stability of halide perovskite solar cells(PSCs).In this study,a benzotriazole derivative(6-chloro-1-hydroxybenzotriazole,Cl-HOBT)is applied to improve the crystallinity and reduce the trap density of methylammonium lead iodide(MAPbI3)perovskite film.Meanwhile,incorporation of Cl-HOBT elongates the photoluminescence carrier lifetime and chargerecombination lifetime,implying the trap-assisted nonradiative recombination is greatly suppressed.Besides,the improved energy level alignment and enhanced built-in potential are conducive to the charge carrier separation and transfer process with Cl-HOBT.Consequently,a PCE of 20.27%and an open-circuit voltage(Voc)of 1.09 V are achieved for the inverted MAPbI3 PSCs,along with an 85%maintaining of the initial PCE under stored at relative humidity of 20%for 500 h.Furthermore,the existence of Cl-HOBT could inhibit the formation of Pb0 defect under prolonged UV illumination to retard the degradation of perovskite film.It is believed that this study paves a novel path for the realization of highefficiency PSCs with UV-stability.

Energy level engineering of charge selective contact and halide perovskite by modulating band offset:Mechanistic insights

Mixed cation and anion based perovskites solar cells exhibited enhanced stability under outdoor conditions,however,it yielded limited power conversion efficiency when TiO_(2) and Spiro-OMeTAD were employed as electron and hole transport layer(ETL/HTL)respectively.The inevitable interfacial recombination of charge carriers at ETL/perovskite and perovskite/HTL interface diminished the efficiency in planar(n-i-p)perovskite solar cells.By employing computational approach for uni-dimensional device simulator,the effect of band offset on charge recombination at both interfaces was investigated.We noted that it acquired cliff structure when the conduction band minimum of the ETL was lower than that of the perovskite,and thus maximized interfacial recombination.However,if the conduction band minimum of ETL is higher than perovskite,a spike structure is formed,which improve the performance of solar cell.An optimum value of conduction band offset allows to reach performance of 25.21%,with an open circuit voltage(VOC)of 1231 mV,a current density JSC of 24.57 mA/cm^(2) and a fill factor of 83.28%.Additionally,we found that beyond the optimum offset value,large spike structure could decrease the performance.With an optimized energy level of Spiro-OMeTAD and the thickness of mixed-perovskite layer performance of 26.56% can be attained.Our results demonstrate a detailed understanding about the energy level tuning between the charge selective layers and perovskite and how the improvement in PV performance can be achieved by adjusting the energy level offset.

Influence of Recombination Centers on the Phase Portraits in Nanosized Semiconductor Films

Influence of recombination centers’ changes on the form of phase portraits has been studied. It has been shown that the shape of the phase portraits depends on the concentration of semiconductor materials’ recombination centers.

Recent advances in elaborate interface regulation of BiVO_(4)photoanode for photoelectrochemical water splitting

Bismuth vanadate(BiVO_(4))is an excellent photoanode material for photoelectrochemical(PEC)water splitting system,possessing high theoretical photoelectrocatalytic conversion efficiency.However,the actual PEC activity and stability of BiVO_(4)are faced with great challenges due to factors such as severe charge recombination and slow water oxidation kinetics at the interface.Therefore,various interface regulation strategies have been adopted to optimize the BiVO_(4)photoanode.This review provides an in-depth analysis for the mechanism of interface regulation strategies from the perspective of factors affecting the PEC performance of BiVO_(4)photoanodes.These interface regulation strategies improve the PEC performance of BiVO_(4)photoanode by promoting charge separation and transfer,accelerating interfacial reaction kinetics,and enhancing stability.The research on the interface regulation strategies of BiVO_(4)photoanode is of great significance for promoting the development of PEC water splitting technology.At the same time,it also has inspiration for providing new ideas and methods for designing and preparing efficient and stable catalytic materials.

A bilateral cyano molecule serving as an effective additive enables high-efficiency and stable perovskite solar cells

The existence of defects in perovskite films is a major obstacle that prevents perovskite solar cells (PSCs) from high efficiency and long-term stability. A variety of additives have been introduced into perovskite films for reducing the number of defects. Lewis base-based additive engineering has been considered as an effective way to eliminate defects, especially the defects caused by the uncoordinated Pb^(2+). In this work, for the first time, a bilateral cyano molecule (succinonitrile, SN) which is a commonly used plasticizer in solid electrolyte of solid-state lithium batteries was selected as an additive to modify organic–inorganic hybrid perovskite films in PSCs. SN is featured with two cyano groups (–C≡N) distributing at both terminals of the carbon chain, providing two cross-linking points to interact with perovskites crystals via coordinating with uncoordinated Pb2+ and forming hydrogen bonds with –NH2 groups in perovskite. It was found that the addition of SN into perovskite precursor solution could effectively reduce defects, particularly inhibit the appearance of Pb0 and thus suppress trap-assisted nonradiative charge carrier recombination. As a result, the efficiency of CH_(3)NH_(3)PbI_(3)(Cl) (MAPbI_(3)(Cl))-based PSCs was improved from 18.4% to 20._(3)% with enhanced long-term stability at N2 and humid air atmosphere. This work provides a facile and effective strategy to enhance the PCE and stability of PSCs simultaneously, facilitating the commercialization of PSCs.

Tri-functionalized TiOxCl4-2x accessory layer to boost efficiency of hole-free, all-inorganic perovskite solar cells

Tin dioxide(SnO2) is generally regarded as a promising electron-transporting layer(ETL) for state-of-theart perovskite solar cells(PSCs), however, the ubiquitous oxygen-vacancy-related defects at SnO2 surface and the large energy difference between conduction band of SnO2 and perovskite layer undoubtedly cause severe charge carrier recombination, resulting in sluggish charge extraction efficiency and non-negligible open-circuit voltage(Voc) loss. Herein, a chlorine-containing TiOxCl4-2x accessory layer is fabricated by immersing SnO2 layer into the TiCl4 aqueous solution to passivate the surface oxygen-vacancy-related defects of SnO2 layer and to set an intermediate energy level at ETL/perovskite interface in all-inorganic cesium lead tri-bromine(CsPbBr3) PSCs. Furthermore, the TiOxCl4-2x layer also improves the infiltration of SnO2 layer surface toward perovskite precursor for high-quality perovskite film. Finally, the hole-free, allinorganic CsPbBr3PSC with a structure of FTO/SnO2/TiOxCl4-2x/Cs0.91Rb0.09PbBr3/carbon achieves a champion efficiency of 10.44% with a Vocas high as 1.629 V in comparison to 8.31% for control device. Moreover, the optimized solar cell presents good stability in 80% humidity in air.

High performance of TiO_(2)/Cu_(x)O photoelectrodes for regenerative solar energy storage in a vanadium photoelectrochemical cell

Photocatalysts for harvesting solar energy to either electricity or chemical fuels have attracted much attention recently, but they have big obstacles such as wide bandgaps and rapid charge recombinations to overcome for final applications. In this study, we investigates a useful method to utilize vanadium redox pairs, which are commonly applied for vanadium redox flow batteries, to diminish charge recombinations and thus to enhance photocurrent response in regenerative solar energy storage. The results reveal significant improvements in photocurrent density by forming cuprous and cupric oxides in TiO_(2)/Cu_(x)O electrodes under solar AM 1.5 illuminations using the vanadium photoelectrochemical storage cell at 0.025 mol L^(-1) of vanadium redox species in the acid electrolytes. In addition, the stabilized photocurrent density of the copper content optimized TiO_(2)/Cu_(x)O electrodes is almost tripled from the TiO_(2) only electrode because the charge recombinations can be mitigated with the content optimized TiO_(2)/Cu_(x)O electrodes. Therefore, the optimized TiO_(2)/Cu_(x)O electrode results in the highest charge storing performance in the catholyte chamber, and the roles of vanadium redox species are also clearly demonstrated.

Cosensitization process effect of D-A-π-A featured dyes on photovoltaic performances

Cosensitization based on two or multiple dyes as "dye cocktails" can hit the target on compensating and broadening light-harvesting region.Two indoline D-A-π-A motif sensitizers(WS-2 and WS-39) that possess similar light response area but distinctly reversed feature in photovoltaic performance are selected as the specific cosensitization couple. That is, WS-2 shows quite high photocurrent but low photovoltage, and WS-39 gives relatively low photocurrent but quite high photo voltage. Due to the obvious "barrel effect",both dyes show medium PCE around8.50%. In contrast with the previous cosensitization strategy mostly focused on the compensation of light response region, herein we perform different cosensitization sequence, for taking insight into the balance of photocurrent and photo voltage, and achieving the synergistic improvement in power conversion efficiency(PCE). Electronic impedance spectra(EIS) indicate that exploiting dye WS-39 with high V_(OC) value as the primary sensitizer can repress the charge recombination more effectively, resulting in superior V_(OC) rather than using dye WS-2 with high J_(SC)as the primary sensitizer. As a consequence, a high PCE value of 9.48% is obtained with the delicate cosensitization using WS-39 as primary dye and WS-2 as accessory dye, which is higher than the corresponding devices sensitized by each individual dye(around 8.48-8.67%). It provides an effective optimizing strategy of cosensitization how to combine the individual dye advantages for developing highly efficient solar cells.

PHOTOCHROMISM AND LUMINESCENCE OF DOPANT CHROMOPHORES THROUGH TWO-PHOTON IONIZATION IN POLYMER FILMS

Two-photon ionization and recombination processes of an aromatic chromophore doped in polymer films werestudied and the features of these processes were discussed in relation to photofunctional polymers, An aromatic moleculehaving low ionization potential, e.g., N,N,N',N'-tetramethyl-p-phenylene diamine doped in poly(methyl methacrylate)(PMMA) film was easily photoionized by intense laser ligh excitation, giving a colored radical cation (photochromism) anda trapped electron in PMMA matrix. As a reversed process, the radical cation recombined with the trapped electron, showingdiscoloration and emitting luminescence, either isothermal luminescence (ITL), or thermoluminescence (TL). In this report,ITL and TL through the charge recombination process were studied and the luminescence was suggested as a mean of the read-out of photorecording.

Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

Recent progress in dye-sensitized solar cells （DSC） research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto Ti02, ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron-hole recombination. Advanced exper- imental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and oppor- tunities for further improvement of dye solar cells are presented.

Can the efficiencies of simplified perovskite solar cells go higher?

In recent years, metal halide perovskites have emerged as star semiconducting materials in the field of optoelectronic devices owing to their fascinating optoelectronic properties. Of particular interest are perovskite solar cells (PSCs), which have witnessed skyrocketing power conversion efficiencies (PCEs) within a short period of time, and were recently certified to reach 25.5%, which is already higher than other thin film photovoltaic technologies[1]. Nevertheless, multiple layers are still needed for state-of-theart PSCs to achieve high PCEs over 21%.

Performance enhancement of ZnO nanowires/PbS quantum dot depleted bulk heterojunction solar cells with an ultrathin Al_2O_3 interlayer

Depleted bulk heterojunction （DBH） PbS quantum dot solar cells （QDSCs）, appearing with boosted short-circuit current density （Jsc）, represent the great potential of solar radiation utilization, but suffer from the problem of increased interfacial charge recombination and reduced open-circuit voltage （Voc）. Herein, we report that an insertion of ultrathin A1203 layer （ca. 1.2 A thickness） at the interface of ZnO nanowires （NWs） and PbS quantum dots （QDs） could remarkably improve the performance of DBH-QDSCs fabricated from them, i.e., an increase of Voc from 449 mV to 572 mV, J^c from 21.90 mA/cm2 to 23.98 mA/cm2, and power conversion efficiency （PCE） from 4.29% to 6.11%. Such an improvement of device performance is ascribed to the significant reduction of the interfacial charge recombination rate, as evidenced by the light intensity dependence on Jsc and Voc, the prolonged electron lifetime, the lowered trap density, and the enlarged recombination activation energy. The present research therefore provides an effective interfacial engineering means to improving the overall performance of DBH-QDSCs, which might also be effective to other types of optoelectronic devices with large interface area.

Heterogeneous FASnI3 Absorber with Enhanced Electric Field for High-Performance Lead-Free Perovskite Solar Cells

Lead-free tin perovskite solar cells(PSCs)have undergone rapid development in recent years and are regarded as a promising ecofriendly photovoltaic technology.However,a strategy to suppress charge recombination via a built-in electric field inside a tin perovskite crystal is still lacking.In the present study,a formamidinium tin iodide(FASnI;)perovskite absorber with a vertical Sn;gradient was fabricated using a Lewis base-assisted recrystallization method to enhance the built-in electric field and minimize the bulk recombination loss inside the tin perovskites.Depth-dependent X-ray photoelectron spectroscopy revealed that the Fermi level upshifts with an increase in Sn;content from the bottom to the top in this heterogeneous FASnI;film,which generates an additional electric field to prevent the trapping of photo-induced electrons and holes.Consequently,the Sn;-gradient FASnI;absorber exhibits a promising efficiency of 13.82%for inverted tin PSCs with an open-circuit voltage increase of 130 mV,and the optimized cell maintains over 13%efficiency after continuous operation under 1-sun illumination for 1,000 h.

Defect-poor BaSn(OH)6 enhanced charge separation for efficient photocatalytic degradation of toluene

Crystal defect is well-known to have a significant effect on the photocatalytic performance of semiconductors. Herein, defect-rich and-poor BaSn(OH)6(BSOH-Sn and BSOH-Ba) photocatalysts were synthesized by exchanging the addition order of Ba and Sn. Results show that the defect-poor BSOH-Ba exhibited more efficient toluene degradation under ultraviolet(UV) light, which could attribute to the great suppression of photogenerated electron-hole(e--h+) pairs recombination by tuning the defect concentration. The low defect concentration in BSOH-Ba finally promotes the charge separation efficiency, the generation of reactive oxygen species(ROS), and the photocatalytic toluene degradation reactions. This work not only provides an effective way to inhibit the recombination of photogenerated carriers and improve the photocatalytic performance, but also promotes the understanding of defective perovskite-type hydroxide for more photoreactions.