Search

Interface modification has been proved to be an effective method to improve the performance of perovskite solar cells (PSCs). In this paper, tetramethylammonium hexafluorophosphate (TMAPF6) is employed to modify the interface of SnO2/perovskite. Fluorine (F) in PF6 − will fill the oxygen vacancy by interacting with Sn in SnO2. Meanwhile, TMA+ and PF6 − in TMAPF6 will effectively fill the MA+ and I− vacancy in the interface. TMAPF6 modification enhances the hydrophobicity of the SnO2 surface, promotes the growth of high-quality perovskite film with large grain size, and then significantly suppresses the non-radiative recombination of PSCs. Furthermore, the TMAPF6 modification introduces a better energy level alignment between SnO2 and perovskite layer, enabling a more efficient electron extraction. As a result, the TMAPF6-modified MAPbI3 PSC achieves a significantly increasing power conversion efficiency (PCE) from 18.62% to 20.92% and an improved stability with only 15% PCE drop after 600 h of storage in air. This work develops an efficient interface modification molecule to increase the efficiency of PSCs, which would be a promising strategy for the large-scale commercialization of the photovoltaic devices.

Owing to the superior properties of the wide bandgap, high carrier mobility, high thermal conductivity and high stability, 4H silicon carbide (4H-SiC) holds great promise for applications in electrical vehicles, 5G communications, and new-energy systems. Although the industrialization of 150 mm 4H-SiC substrates and epitaxial layers has been successfully achieved, the existence of a high density of dislocations is one of the most severe bottlenecks for advancing the performance and reliability of 4H-SiC based high-power and high-frequency electronics. In this topical review, the classification and basic properties of dislocations in 4H-SiC are introduced. The generation, evolution, and annihilation of dislocations during the single-crystal growth of 4H-SiC boules, the processing of 4H-SiC wafers, as well as the homoepitaxy of 4H-SiC layers are systematically reviewed. The characterization and discrimination of dislocations in 4H-SiC are presented. The effect of dislocations on the electronic and optical properties of 4H-SiC wafers and epitaxial layers, as well as the role of dislocations on the performance and reliability of 4H-SiC based power devices are finally presented. This topical review provides insight into the fundamentals and evolution of dislocations in 4H-SiC, and is expected to provide inspiration for further control of dislocations in 4H-SiC.

Solution-processed organic/inorganic hybrid halide perovskites are a class of very promising photovoltaic materials because of their extraordinary optoelectronic properties. However, numerous intrinsic defects within perovskite films limit the performance enhancement of perovskite solar cells (PSCs). Herein, we introduce three different alkali metal fluoride additives into the perovskite precursor to modulate the defect behaviors. The addition of alkali metal fluorides, especially potassium fluoride (KF), significantly passivates grain boundaries and point defects within bulk perovskite films, contributing to increased carrier lifetime and reduced defect state density. By optimizing the concentration of additives, the PSC device with 1% KF added has realized a significantly enhanced power conversion efficiency of 20.11%, and ignorable hysteresis.

The impact of dislocations on oxygen vacancies in un-doped SrTiO3 single crystal has been investigated by cathodoluminescence (CL). The dominated luminescence peak located at ~ 2.8 eV is originated from oxygen vacancies. Enhanced luminescence has been observed at specific dislocations with the accumulation of oxygen vacancies. Under annealing either in oxidizing or reducing atmosphere, the diffusivity of oxygen ions at dislocation cores is nearly the same as that in the bulk. CL results suggest that the accumulation of oxygen vacancies is easily triggered by dislocations, while the diffusion of oxygen vacancies may not be significantly affected.

The effect of post-deposition rapid thermal annealing (RTA) on p-type Czochralski silicon surface passivation by plasma-enhanced chemical vapor deposited nitrogen-rich silicon nitride (SiN x ) films has been investigated. The effective carrier lifetime is significantly improved after annealing at low temperature (400 °C–450 °C) for 15–30 s. This improvement is associated with a decrease of N–H and Si–H bond densities in SiN x films and, a resultant decreased density of states at the SiN x /Si interface. More importantly, the polarity of fixed charges is converted from positive to negative in the annealed SiN x films. It is demonstrated that a release of hydrogen atoms to the SiN x /Si interface combined with a tuning of charges during low-temperature RTA, is very beneficial for p-type silicon surface passivation.

Fullerene (C60) has been demonstrated, using vapor deposition, to be a good electron transport layer (ETL) and different thicknesses have been utilized in n-i-p configuration perovskite solar cells. However, an underlying reason for the variation in thicknesses, which hinders the reproducibility of perovskite solar cells employing a C60 ETL, has not been well-examined. This study reveals that the surface roughness of the conducting glass, such as fluorine doped tin oxide (FTO), affects the photovoltaic performance while optimizing the thickness of the vacuum deposited compact C60 ETL. A low-thickness C60 ETL retains a surface roughness and Ohmic behavior similar to bare FTO due to physical defects at the C60/FTO interface. Increasing the thickness further reduces the defects at the C60/FTO interface and facilitates an enhanced electron extraction from a vacuum co-deposited methyl-ammonium lead iodide perovskite light absorber. As a result, a perovskite solar cell with a homogenously covered C60 ETL on an FTO substrate delivers a power conversion efficiency of 14.63%. These comprehensive characterizations support the finding that suppression of defects at the C60/FTO interface results in an improved photovoltaic performance. This work demonstrates that the surface roughness of FTO needs to be considered for a decisive compact ETL for enhanced photovoltaic performance and reproducibility.

Using first-principles calculations, we report on charge injection induced switching between ferromagnetic (FM) and antiferromagnetic (AFM) in a 2H- monolayer. monolayers doped with different transition metals (TM)—Fe and Mn—initially demonstrate FM and AFM magnetic ground state, respectively. Once the injected charge approaches e/unit, the systems respectively tend to AFM and FM states, due to the modulation effect of the exchange splitting of spins via injected charge. The interesting switch between FM and AFM can be explained by the competition between FM double-exchange and AFM super-exchange interaction. In contrast, the / heterojunction, because of the direct bonding between dopant TM atoms, remains in the AFM state even under charge injection. These findings point toward the possible development of spintronic switch devices using charge injection in TM doped materials, which could be pivotal to information storage and spintronic applications.

Cotton cellulose nanofibers (CCNFs)/In2S3/Ag–CdS nanocomposites were prepared by a typical technical route which combined electrospinning and a chemical method. The results showed that the CCNFs/In2S3/Ag–CdS nanocomposites had a remarkable visible light photocatalytic property and cycling stability, which displayed a significant enhancement compared with that of pure In2S3. Through analysis, this enhancement could be mainly attributed to the multilevel structure of the composites.

Tungsten doped tin oxide thin film transistors (TWO-TFTs) were fabricated by radio frequency magnetron sputtering. With TWO thin films as the channel layers, the TFTs show lower off-current and positive shift turn-on voltage than the intrinsic tin oxide TFTs, which can be explained by the reason that W doping is conducive to suppress the carrier concentration of the TWO channel layer. It is important to elect an appropriate channel thickness for improving the TFT performance. The optimum TFT performance in enhancement mode is achieved at W doping content of 2.7 at% and channel thickness of 12 nm, with the saturation mobility, turn-on voltage, subthreshold swing value and on–off current ratio of 5 cm2 V−1 s−1, 0.4 V, 0.4 V/decade and 2.4 × 106, respectively.