Regulating Effect of Substrate Temperature on Sputteringgrown Ge/Si QDs under Low Ge Deposition

The effect of deposition temperature on the morphology and optoelectronic performance of Ge/Si QDs grown by magnetron sputtering under low Ge deposition(~4 nm)was investigated by atomic force microscopy,Raman spectroscopy,and photoluminescence(PL)tests.The experimental results indicate that temperatures higher than 750℃effectively increase the crystallization rate and surface smoothness of the Si buffer layer,and temperatures higher than 600℃significantly enhance the migration ability of Ge atoms,thus increasing the probability of Ge atoms meeting and nucleating to form QDs on Si buffer layer,but an excessively high temperature will cause the QDs to undergo an Ostwald ripening process and thus develop into super large islands.In addition,some PL peaks were observed in samples containing small-sized,high-density Ge QDs,the photoelectric properties reflected by these peaks were in good agreement with the corresponding structural characteristics of the grown QDs.Our results demonstrate the viability of preparing high-quality QDs by magnetron sputtering at high deposition rate,and the temperature effect is expected to work in conjunction with other controllable factors to further regulate QD growth,which paves an effective way for the industrial production of QDs that can be used in future devices.

Enhanced Crystal Quality of Perovskite via Protonated Graphitic Carbon Nitride Added in Carbon-Based Perovskite Solar Cells

The quality of perovskite layers has a great impact on the performance of perovskite solar cells(PSCs).However,defects and related trap sites are generated inevitably in the solutionprocessed polycrystalline perovskite films.It is meaningful to reduce and passivate the defect states by incorporating additive into the perovskite layer to improve perovskite crystallization.Here an environmental friendly 2D nanomaterial protonated graphitic carbon nitride(p-g-C_(3)N_(4))was successfully synthesized and doped into perovskite layer of carbon-based PSCs.The addition of p-g-C_(3)N_(4)into perovskite precursor solution not only adjusts nucleation and growth rate of methylammonium lead tri-iodide(MAPb I3)crystal for obtaining flat perovskite surface with larger grain size,but also reduces intrinsic defects of perovskite layer.It is found that thep-g-C_(3)N_(4) locates at the perovskite core,and the active groups-NH_(2)/NH_(3)and NH have a hydrogen bond strengthening,which effectively passivates electron traps and enhances the crystal quality of perovskite.As a result,a higher power conversion efficiency of 6.61% is achieved,compared with that doped with g-C_(3)N_(4)(5.93%)and undoped one(4.48%).This work demonstrates a simple method to modify the perovskite film by doping new modified additives and develops a low-cost preparation for carbon-based PSCs.

Optical and electrical properties of room temperature preparedα-IGZO thin films using an In_(2)Ga_(2)ZnO_(7) ceramic target

In this study,a high-purity In_(2)Ga_(2)ZnO_(7) ceramic target was used to deposit indium gallium zinc oxide(IGZO)films by RF magnetron sputtering technology.The microstructure,growth state,optical and electrical properties of the IGZO films were studied.The results showed that the surface of the IGZO film was uniform and smooth at room temperature.As the substrate temperature increased,the surface roughness of the film gradually increased.From room temperature to 300℃,all the films maintained amorphous phase and good thermal stabilities.Moreover,the transmission in the visible region decreased from 91.93%to 91.08%,and the band gap slightly decreased from 3.79 to 3.76 eV.The characterization of the film via atomic force microscope(AFM)and X-ray photoelectron spectroscopy(XPS)demonstrated that the film prepared at room temperature exhibited the lowest surface roughness and the largest content of oxygen vacancies.With the rise in temperature,the non-homogeneous particle distribution,increase in the surface roughness,and reduction in the number of oxygen vacancies resulted in lower performance of theα-IGZO film.Comprehensive analysis showed that the best optical and electrical properties can be obtained by depositing IGZO films at room temperature,which indicates their potential applications in flexible substrates.

Molecular engineering of s-triazine and its derivatives applied in surface modification strategy for enhancing photoelectric performanc of all-inorganic perovskites

We develop the effective modification strategy based on molecular engineering of s-triazine and its derivatives to improve the photoelectric performance of all-inorganic perovskites(AIP)for the first time.The surface modification strategy with cyanuric acid successfully increases the PLQY of AIP from 40.55%to 88.15%,and significantly enhances the current of the AIP film under 3 V by almost 20-fold(from4.44 m A to 81.20 m A).This work has proven the effectiveness of improving the photoelectric performances of AIP via s-triazine and its derivatives and also suggested the potential risks of reducing the photoelectric performance of AIP due to inappropriate substituents in conjugated organic ligands.

Photoelectric characteristics of an inverse U-shape buried doping design for crosstalk suppression in pinned photodiodes

A design of an inverse U-shape buried doping in a pinned photodiode （PPD） of CMOS image sensors is proposed for electrical crosstalk suppression between adjacent pixels. The architecture achieves no extra fill factor consumption, and proper built-in electric fields can be established according to the doping gradient created by the injections of the extremely low P-type doping buried regions in the epitaxial layer, causing the excess electrons to easily drift back to the photosensitive area rarely with a diffusion probability; the overall junction capacitance and photosensitive area extensions for a full well capacity （FWC） and internal quantum efficiency （IQE） improving are achieved by the injection of a buried N-type doping. By considering the image lag issue, the process parameters of all the injections have been precisely optimized. Optical simulation results based on the finite difference time domain method show that compared to the conventional PPD, the electrical crosstalk rate of the proposed architecture can be decreased by 60%-80% at an incident wavelength beyond 450 nm, IQE can be clearly improved at an incident wavelength between 400 and 600 nm, and the FWC can be enhanced by 107.5%. Furthermore, the image lag performance is sustained to a perfect low level. The present study provides important guidance on the design of ultra high resolution image sensors.

Advances in Polymethine Dyes for Near-Infrared Organic Photodiodes

Near-infrared organic photodiodes (NIR OPDs) have tremendous potential in industrial, military, and scientific applications, due to their unique features of lightweight, low toxicity, high structural flexibility, cooling-system-free, etc. However, the overall performance of currently available NIR OPDs still lags behind the commercial inorganic photodetectors, ascribed to the critical challenge of realizing organic semiconductors with sufficiently low optical bandgap and excellent optoelectronic properties simultaneously. Among various types of NIR-absorbing organic semiconductors, polymethine dyes not only possess advantages of simple synthesis and structural diversity, but also show fascinating optical and aggregation features in the solid state, making them attractive material candidates for NIR OPDs. In this review, after a brief introduction of NIR OPDs and polymethine dyes, we comprehensively summarize the advances of polymethine dyes for broadband and narrowband NIR OPDs, and further introduce their applications in all-organic optical upconversion devices and photoplethysmography sensors. In particular, the relationship between the chemical structure and the aggregation behaviors of polymethine dyes and the device performance is carefully discussed, providing some important molecular insights for developing high performance NIR OPDs.

Vapor-Phase Precise-Synthesis of 2D Inorganic Materials for Optoelectronics

Comprehensive Summary 2D materials have attracted intensive attention due to their unique electrical and optical properties associated with their strictly defined low dimensionalities.They provide a wide range of basic building blocks for future electronics and optoelectronics.The chemical vapor deposition(CVD)has been proposed to be efficient to realize the controllable thickness,scalable size,which are necessary for both industrial applications and fundamental researches.Herein,we share our research works to realize the controllable growth of 2D materials.We found that stable growth microenvironment can regulate the growth of 2D materials.Thus,we developed near-steady source supply,space-confined,and additive-assisted passivated growth methods to solve the problem of unstable growth environment caused by uneven source and mass transfer.Then,we developed several strategies to precisely control the parity,separation,and transport of the carriers in 2D materials including fabricating defect-free interface via van der Waals dielectrics,modulating the parity of carriers via ferroelectric-field,and the separation of carriers via band engineering.Toward future development,we highlight the opportunities and challenges inthis field.

A Composite Photoanode Based on P25/TiO2 Nanotube Arrays/ Flower-Like TiO2 for High-Efficiency Dye-Sensitized Solar Cells

In this work, a three-layer TiO2 composite film consisting of flower-like TiO2 （Flo-TiO2） as overlayer, TiOa nanotube arrays as interlayer and TiO2 nanoparticle （P25） as underlayer was fabricated as the photoelectrode of dyesensitized solar cells （DSSCs）. Due to the introduction of Flo-TiO2, the three-layer composite film has strong lightscattering ability. Then, we have investigated and compared the photoelectric conversion properties of DSSCs based on three-layer structure （P25/TNT arrays/Flo-TiO2） photoelectrode and double-layer film （P25/TNT arrays） photoelectrode. It is found that DSSCs based on three-layer structure exhibit a high power conversion efficiency of 6.48% compared with the DSSCs composed of double-layer film （5.11%）.