Extent of Shallow/Deep Trap States beyond the Conduction Band Minimum in Defect-Tolerant CsPbBr <sub/>3</sub> Perovskite Quantum Dot: Control over the Degree of Charge Carrier Recombination

摘要： Perovskite quantum dots (PQDs) are known to be defect tolerant possessing clean band-gap with optically inactive benign defect states. However, we show that there exists significant deep trap states beyond conduction band minimum, although the extent of shallow trap states is observed to be minimal. Extent of deep trap states beyond conduction band minimum seem to significant in PQD, however the extent is less than even optically robust CdSe and InP based core/alloy-shell QDs. In-depth analyses based on ultrafast transient absorption and ultrasensitive single particle spectroscopic investigations decode the underlying degree of charge carrier recombination in CsPbBr3 PQD which are quite important for energy applications.

Phenanthrenea??Fuseda??Quinoxaline as Key Building Block for Highly Efficient and Stable Sensitizers in Copper Electrolyte Based Dyea??Sensitized Solar Cells

摘要： Dye-sensitized solar cells (DSSCs) based on Cu(II/I) bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open-circuit voltages (VOC, > 1 V). However, their short-circuit photocurrent density (JSC) has remained modest. The challenge for increasing the JSC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO2 film and fast regeneration by the Cu(I) complex. Here, we report two new D-A-π-A featured sensitizers coded HY63 and HY64, which employ either benzothiadiazole (BT) or phenanthrene-fused-quinoxaline (PFQ) as the auxiliary electron-withdrawing acceptor moiety. In spite of very similar energy levels and absorption onsets, HY64-based DSSCs outperform largely their HY63 counterpart, achieving an outstanding power conversion efficiency (PCE) of 12.5% with superior stability. In depth studies of interfacial charge carrier dynamics show that PFQ is superior to BT in retarding charge recombination resulting in near quantitative collection of photogenerated charge carriers.

Enhancing Grain Growth for Efficient Solution-Processed (Cu,Ag) <sub/>2</sub> ZnSn(S,Se) <sub/>4</sub> Solar Cells Based on Acetate Precursor

摘要： Material crystallinity is the overriding factor in the determination of the photoelectric properties of absorber materials and the overall performance of photovoltaic device. Nevertheless, in Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic device the bilayer or tri-layer structure for the absorber have been broadly observed, which are generally harmful to the cell performance due to the probability of photogenerated carrier recombination at grain boundaries significantly increased. Herein, our experiment reveals that application of anions to a new family of (Cu,Ag)2ZnSn(S,Se)4 (CAZTSSe) materials leads to the increase of grain size and crystallinity. It is inspiring that by using acetate starting materials in precursor solution, a uniform, compact and pinhole-free CAZTS precursor film was obtained, and the smoothness of the films surpassed that of films fabricated from oxide route. More importantly, the crystallization of the CAZTSSe film has been considerably enhanced after selenization, large grains go through the entire absorber layer was successfully obtained. Additionally, it is observed that the Voc accompanied by excellent crystallinity improved significantly due to the pronouncedly reduced carrier recombination loss at grain boundaries. As a consequence, the power conversion efficiency (PCE) of the CAZTSSe photovoltaic device is successfully increased from 10.35% (oxide route) to 11.32% (acetate route). Importantly, our work attest to the feasibility of tuning the crystallization of the CZTSSe film by simple chemistry.

Influence of nonradiative Auger process in the lanthanide complexes lifetime near interfaces in organic light-emitting diode structures

摘要： The low efficiency of organic light-emitting diodes based on lanthanide complexes is generally attributed to the triplet-triplet annihilation processes in the regime of high concentration of excited states caused by their long lifetimes and optical losses near the interfaces of multilayer device structures. Despite the enormous effort to synthesize short-lived complexes and minimize the optical losses in the interfaces, it remains insufficient in understanding the exciton recombination processes that reduce the lifetime of these complexes. Herein, we investigated the influence of the exciton recombination processes on a Tb complex (Tb-C) lifetime in the regime of a highly excited state concentration as a function of the distance between the carrier layer and the interface by using a typical organic light-emitting diode structure. Our results show that a 10 nm-thick Alq3 layer decreases the exciton lifetime of the Tb-C, increasing approximately by 16 times the spontaneous emission decay rate of triplet exciton. The effects of interference and optical losses at the metallic interface contribute actively to the modulation of the emission intensity and lifetime decay. However, these effects alone do not explain the significant increase in the emission decay rate. The nonradiative Auger process at the Alq3/Tb-C interface seems to be largely accountable for the Tb-C lifetime reduction as the energy released by the terbium ion occurs by the excitation of an adjacent electron at higher energy. Furthermore, we propose a simple theoretical model to explain the observed effects. These results can provide a new approach to reduce the lanthanide complexes’ lifetime through the Auger electron process near the interface and thus improve the performance of organic light-emitting diodes.

Corrigendum: Impact of Polymer Backbone Fluorination on the Charge Generation/Recombination Patterns and Vertical Phase Segregation in Bulk Heterojunction Organic Solar Cells

Effects of interfacial energy level alignment on carrier dynamics and photovoltaic performance of inverted perovskite solar cells

摘要： Metal doping is an efficient method for optimizing NiOx as hole transport material in the inverted perovskite solar cells, which can contribute to the optimization of the interfacial energy level alignment, while the underlying influencing mechanism on the charge carrier dynamics and device performance needs to be further elucidated. In this work, NiOx films with modulated energy levels are obtained via Li doping and examined by ultraviolet photoelectron spectrometer. The effects of the energy level alignment of NiOx on the carrier transfer and recombination dynamics are elucidated by transient photovoltage/photocurrent and transient fluorescence dynamics. The Li doping can significantly shift the valence band of NiOx downward, and the 4% Li content endows NiOx with the optimal energy level matching with perovskite and the best charge separation/transfer ability, which can be confirmed through the photoluminescence results. The corresponding device possesses superior photovoltaic parameters with the champion power conversion efficiency of 17.34%, 37% higher than device based on pure NiOx. The results highlight that proper metal doping can optimize the energy level of the hole transport material to well match the perovskite, thus efficiently promoting charge separation and inhibiting charge recombination, which leads to the enhancement of the device performances.

Controlled Growth and Bandstructure Properties of One Dimensional Cadmium Sulfide Nanorods for Visible Photocatalytic Hydrogen Evolution Reaction

摘要： One dimensional (1D) metal sulfide nanostructures are one of the most promising materials for photocatalytic water splitting reactions to produce hydrogen (H2). However, tuning the nanostructural, optical, electrical and chemical properties of metal sulfides is a challenging task for the fabrication of highly efficient photocatalysts. Herein, 1D CdS nanorods (NRs) were synthesized by a facile and low-cost solvothermal method, in which reaction time played a significant role for increasing the length of CdS NRs from 100 nm to several micrometers. It is confirmed that as the length of CdS NR increases, the visible photocatalytic H2 evolution activity also increases and the CdS NR sample obtained at 18 hr. reaction time exhibited the highest H2 evolution activity of 206.07 μmol.g-1.h-1. The higher H2 evolution activity is explained by the improved optical absorption properties, enhanced electronic bandstructure and decreased electron-hole recombination rate.

Evaluating the performance of InGaN/GaN multi-quantum-well solar cells operated at elevated temperatures via DC and small-signal AC analysis

摘要： InGaN/GaN multi-quantum-well (MQW) solar cells are investigated with temperature-dependent DC and AC analysis, and the effects of differing QW number and thickness are determined. The carrier transport is shown to be dominated by thermionic emission rather than tunneling at elevated temperature but limited by recombination outside the depletion region. Temperature-dependent AC parameters of the III-N MQW devices in high-level injection are determined through a refined AC circuit model of the device. It is shown that the use of AC small-signal analysis and its ability to extract stored charge in the QWs, the comparison of built-in potential to VOC, and other solar cell critical values allows a device designer insight not possible via DC analysis alone. This critical data suggests that the number of QWs and total depletion volume needs to be matched to the operational temperature of a given high temperature solar cell.

Tri-functionalized TiO Cl4-2 accessory layer to boost efficiency of hole-free, all-inorganic perovskite solar cells

摘要： Tin dioxide (SnO2) is generally regarded as a promising electron-transporting layer (ETL) for state-of-the-art 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, all-inorganic CsPbBr3 PSC with a structure of FTO/SnO2/TiOxCl4-2x/Cs0.91Rb0.09PbBr3/carbon achieves a champion efficiency of 10.44% with a Voc as 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.

Long lifetime g-C3N4 photocatalyst coupled with phosphorescent material working under dark condition

摘要： Existing photocatalysts suffer from decreased photocatalytic efficiency when illuminated at wavelengths beyond the UV region or in the absence of irradiation. To overcome this disadvantage, graphitic carbon nitride (g-C3N4), which is responsive to visible light, was coupled with a phosphorescent material (SEAD) that emits green light after irradiation is discontinued. The excited electron and holes in the as-made SEAD/g-C3N4 undergo slow recombination; thus, the material exhibited better performance than g-C3N4 based on photocurrent measurement. We demonstrated the performance of the samples via photodegradation experiments using three organic dyes; methylene blue (MB), methyl orange (MO), and rhodamine B (RhB). The results show that g-C3N4 coupled with the phosphorescent material exhibited better efficiency for photocatalytic degradation of organic dyes than g-C3N4 alone under dark condition as well as light irradiation. In addition, the decomposition of the dyes continued even after irradiation was discontinued, due to phosphorescence.