Jiangsheng Li

Morphological, physiological, and biochemical responses of Populus euphratica to soil flooding

The riparian forests along the Tarim River, habitats for Populus euphratica establishment, are subjected to frequent flooding. To elucidate adaptive strategies that enable this species to occupy the riparian ecosystem subjected to seasonal or permanent water-logging, we examined functional characteristics of plant growth, xylem water relations, leaf gas exchange, chlorophyll (Chl) content and fluorescence, soluble sugar and malondialdehyde (MDA) content in P. euphratica seedlings flooded for 50 d. Although flooded seedlings kept absorbing carbon throughout the experiment, their shoot and root growth rates were lower than in non-flooded seedlings. The reduced leaf gas exchange and quantum efficiency of PSII of flooded seedlings resulted possibly from the reduction in total Chl content. Content of soluble sugar and malondialdehyde in leaves were higher in flooded than in control seedlings. Soil flooding induced hypertrophy of lenticels and increased a stem diameter. These responses were responsible for species survival as well as its success in this seasonally flooded riparian zone. Our results indicate that P. euphratica is relatively flood-tolerant due to a combination of morphological, physiological, and biochemical adjustments, which may support its dominance in the Tarim riparian forest.

Inverted polymer solar cells with enhanced fill factor by inserting the potassium stearate interfacial modification layer

A thin potassium stearate (KSt) film combined with an optimized ZnO film was introduced to improve the fill factor (FF) of highly efficient inverted polymer solar cells (PSCs). Atomic force microscopy and contact angle measurements were used to show that the introduction of KSt did not change the morphology of interlayer. On the contrary, it is beneficial for the spread of the active layer on the interlayer. The origin of enhanced FF was systematically studied by the ideal current-voltage model for a single heterojunction solar cell and electrochemical impedance spectroscopy. On the basis of the data analysis, the reduced charge recombination loss was responsible for this improved FF. At last, when KSt was replaced by sodium stearate (NaSt), the similar experiment phenomenon was observed. This indicates that inserting a metallic stearate modified layer is a promising strategy to enhance inverted PSCs performance.

Facile preparation and characterization of ZnCdS nanocrystals for interfacial applications in photovoltaic devices

Recently, ZnCdS nanocrystals (NCs) have attracted intense attention because of their specific optical properties and electrical characteristics. In this paper, a green and facile solution method is reported for the preparation of ZnCdS nanocrystals using dimethylsulfoxide as small molecular ligands. The ZnCdS nanocrystals are used as an interface modification material in the photovoltaic devices. It is found that the modification of ZnCdS on TiO2 surface not only suppresses the recombination loss of carriers but also reduces the series resistance of TiO2/active layer. Consequently, both of the short circuit current (Jsc) and the fill factor (FF) of the solar cells were significantly improved. Power conversion efficiency (PCE) of 7.75% based on TiO2/ZnCdS was achieved in contrast to 6.65% of the reference devices based on pure TiO2 film in organic solar cells. Furthermore, the PCE of perovskite solar cells based on TiO2/ZnCdS was observed with 8.3% enhancement compared to that of pure TiO2-based ones.

Controllable Spatial Configuration on Cathode Interface for Enhanced Photovoltaic Performance and Device Stability

The molecular structure of cathode interface modification materials can affect the surface morphology of the active layer and key electron transfer processes occurring at the interface of polymer solar cells in inverted structures mostly due to the change of molecular configuration. To investigate the effects of spatial configuration of the cathode interfacial modification layer on polymer solar cells device performances, we introduced two novel organic ionic salts (linear NS2 and three-dimensional (3D) NS4) combined with the ZnO film to fabricate highly efficient inverted solar cells. Both organic ionic salts successfully decreased the surface traps of the ZnO film and made its work function more compatible. Especially NS4 in three-dimensional configuration increased the electron mobility and extraction efficiency of the interfacial film, leading to a significant improvement of device performance. Power conversion efficiency (PCE) of 10.09% based on NS4 was achieved. Moreover, 3D interfacial modification could retain about 92% of its initial PCE over 160 days. It is proposed that 3D interfacial modification retards the element penetration-induced degradation without impeding the electron transfer from the active layer to the ZnO film, which significantly improves device stability. This indicates that inserting three-dimensional organic ionic salt is an efficient strategy to enhance device performance.

Improving the efficiency of inverted organic solar cells by introducing ferrocenedicarboxylic acid between an ITO/ZnO interlayer

In this study, ferrocenedicarboxylic acid (FDA) has been introduced between an ITO electrode and ZnO interlayer to improve the performance of inverted polymer solar cells. The highest power conversion efficiency (PCE) of 9.06% is achieved among the measurements. Besides, the average PCE of FDA/ZnO based devices is observed with 11.9% enhancement (8.73% vs. 7.80%) compared to ZnO-only devices. Electrical characterization, surface morphology, wetting properties, as well as exciton generation rate and dissociation probability were investigated to understand the impact of FDA insertion on the interfacial properties. It was found that exciton dissociation efficiency and charge collection efficiency were significantly improved after inserting FDA, while the surface morphology, average roughness and water contact angle of the ZnO film were not changed. It was thought that FDA connected to the ITO electrode and ZnO film because of its carboxyl groups, which lead to a compact interfacial contact and reduced charge recombination. In addition, the devices based on the FDA/ZnO interlayers displayed improved stability in the argon-filled glove box without any encapsulation for about 1000 h compared to the ZnO-only devices. This study provides a new idea to introduce materials with functional groups between ITO/metal oxides interfaces to achieve more efficient charge collection and device performance.

Graphdiyne as a Host Active Material for Perovskite Solar Cell Application

This work demonstrates a novel photovoltaic application in which graphdiyne (GD) can be employed as a host material in a perovskite active layer for the first time. In the device fabrication, the best molar ratio for active materials is verified as PbI2/MAI/GD being 1:1:0.25, yielding a peak power-conversion efficiency of 21.01%. We find that graphdiyne, as the host material, exerts significant influence on the crystallization, film morphology, and a series of optoelectronic properties of the perovskite active layer. A uniform MAPbI3 film with highly crystalline qualities, large domain sizes, and few grain boundaries was realized with the introduction of graphdiyne. Moreover, the current-voltage hysteresis was negligible, and device stability was significantly improved as well. The results indicate that graphdiyne as the host active material presents great potential for the enhancement of the performance of perovskite solar cells.

Ternary CuZnS Nanocrystals: Synthesis, Characterization, and Interfacial Application in Perovskite Solar Cells

Ternary CuZnS nanocrystals (NCs) are synthesized via a facile, scalable, noninjection method at low temperatures for the first time, wherein sodium ascorbate plays the dual roles of reducing agent and capping ligand in the preparation process. These NCs can be dispersed well in a polar solvent like dimethyl sulfoxide, and the average size is ∼4 nm as measured by transmission electron microscopy. The results of X-ray diffraction and X-ray photoelectron spectroscopy indicate that the crystal structure of CuZnS NCs displays covellite CuS-like structure and the Zn element partly occupies the Cu position. Also, the crystal structure of CuZnS NCs is completely converted from a covellite CuS structure into a digenite Cu9S5 structure when the NCs are treated above 350 °C. Moreover, CuZnS NCs demonstrate favorable hole transport properties. When it is employed in MAPbI3-based perovskite solar cells as a hole transport layer, a peak power conversion efficiency of 18.3% is achieved. Simultaneously, the devices based on CuZnS exhibit a remarkably reduced J-V hysteresis. The results indicate that CuZnS is a promising hole transport layer for enhancing perovskite solar cell performance and presents great potential for optoelectronic applications, as well.

Performance Enhancement of Inverted Perovskite Solar Cells Based on Smooth and Compact PC61BM:SnO2 Electron Transport Layers

In this work, PC61BM:SnO2 electron transport layers (ETLs) were applied in inverted CH3NH3PbI3 perovskite solar cells, and a high power conversion efficiency of 19.7% could be obtained. It increased by 49.0% in comparison with the device based on PC61BM-only ETL (13.2%). SnO2 nanocrystals with excellent dispersibility were employed here to fill the pinholes and cover the valleys of PC61BM layer, forming smooth and compact PC61BM:SnO2 layers. Simultaneously, the electron traps caused by deep-level native defects of SnO2 were reduced by PC61BM, proved by the space charge limited current analysis. Thus, PC61BM:SnO2 ETLs can inhibit both of the defects in PC61BM and SnO2 layers which contribute to the electron transport improvement and reduce the recombination loss. Moreover, the device stability based on the bilayer was significantly improved in comparison with the PC61BM-only device and the performance of 85% could be maintained after 1 month.

Graphdiyne-Doped P3CT-K as an Efficient Hole-Transport Layer for MAPbI3 Perovskite Solar Cells

Here we reported the doping of graphdiyne in P3CT-K in MAPbI3 perovskite solar cells as hole-transport materials. The doping could improve the surface wettability of P3CT-K, and the resulting perovskite morphology was improved with homogeneous coverage and reduced grain boundaries. Simultaneously, it increased the hole-extraction mobility and reduced the recombination as well as improved the performance of devices. Therefore, a high efficiency of 19.5% was achieved based on improved short-circuit current and fill factor. In addition, hysteresis of the J- V curve was also obviously reduced. This work paves the way for the development of highly efficient perovskite solar cells.