Understanding Auger recombination in perovskite solar cells.

Enhanced radiative efficiency, long carrier lifetimes, and high carrier mobilities are hallmarks of perovskite solar cells. Considering this, complete cells experience large nonradiative recombination losses that restrict their VOC considerably below the Shockley-Queisser limit. Auger recombination, which involves two free photo-induced carriers and a trapped charge carrier, is one potential mechanism. Herein, the effects of Auger capture coefficients in mixed-cation perovskites are analyzed employing SCAPS-1D computations. It is demonstrated that VOC and FF are severely decreased with an increase in the acceptor concentration and Auger capture coefficients of perovskites, thus reducing the device performance. When the Auger capture coefficient is increased to 10-20 cm6 s-1 under the acceptor concentration of 1016 cm-3, the performance is drastically lowered from 21.5% (without taking Auger recombination into account) to 9.9%. The findings suggest that in order to increase the efficiency of perovskite solar cells and prevent the effects of Auger recombination, the Auger recombination coefficients should be less than 10-24 cm6 s-1.

Interface engineering of heterogeneous NiMn layered double hydroxide/vertically aligned NiCo2S4 nanosheet as highly efficient hybrid electrocatalyst for overall seawater splitting.

We report the fabrication of a heterogeneous catalyst through vertically aligned NiCo2S4/Ni3S2 nanosheet with encapsulation of ultrathin NiMn layered double hydroxide over self-standing nickel foam (NM/NCS/NS/NF) via two-step hydrothermal processes. Benefiting from more adequate catalytic active centres and copious interfacial charge transfer channels, NM/NCS/NS/NF electrode demonstrates superior bifunctional activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes under alkaline fresh/simulated seawater electrolyte conditions. As a result, NM/NCS/NS/NF electrode requires the smallest overpotentials of 282 & 312 mV (OER) and 171 & 204 mV (HER) to attain current densities of 30 & 50 mA cm-2 respectively under alkaline simulated seawater electrolyte conditions. Besides, the presence of amorphous NiMn LDH layers over crystalline NiCo2S4/Ni3S2 catalyst stimulates surface adsorption of oxygen intermediate species, water dissociate ability on catalytic active centres, and mass transport with electron transfer at the interface. Further, the two-electrode configuration assisted electrolyser system delivers an efficient overall water splitting activity with minimum cell voltages of 1.54 V (in 1 M KOH) and 1.56 V (in 1 M KOH+0.5 M NaCl) at a current density of 10 mA cm-2. Besides, a fabricated electrolyser cell provides a more sustained water electrolysis process and robust durability for 20 h which displays NM/NCS/NS/NF electrode is a vibrant and potential candidate for realistic seawater electrolysis. Therefore, our proposed heterogeneous electrocatalyst could open up a new platform for developing efficient large-scale efficient seawater electrolysis.

Simulation and analysis of lead-free perovskite solar cells incorporating cerium oxide as electron transporting layer.

The great demand for renewable energy has greatly contributed to the development of the solar cell industry. Recently, silicon solar cells have dominated the world market. The ease of processing gives perovskite solar cells (PSCs) an advantage over conventional silicon solar cells. Regular silicon photovoltaics require expensive, multi-step processes accomplished in a specialized ultraclean-chamber facility at an elevated temperature (>1000 °C) and highly vacuumed workspace. Hence, researchers and the solar cell industry have focused on PSC as a great rival to silicon solar cells. Despite this, the highest efficiency was obtained from lead-based PSC, which has a considerably high toxicity issue and low stability related to lead content, so the research field pays attention to lead-free perovskite solar cells. In this digital simulation, tin-based perovskite in this paper, methylammonium tin iodide (MASnI3) with the use of cerium oxide (CeO x ) as an electron transporting layer (ETL) with varying percentages of oxygen, which means different shallow donor densities (ND). The optimum value for the thickness of the absorber layer (perovskite) was made, and the current-voltage characteristics and efficiency calculations were also accomplished for the best cell. Then an improvement was made by changing the ND value of CeO x , and the best-optimized cell parameters were: open circuit voltage (V OC) of 0.92 V, short circuit current density (J SC) of 30.79 mA cm-2, power conversion efficiency (PCE) of 17.77%, and fill factor (FF) of 62.86%.

Influence of microwave power on the preparation of NiO nanoflakes for enhanced magnetic and supercapacitor applications.

Nanoflake-structured NiO were synthesized by a microwave assisted method without the use of additives. The cubic phase of NiO nanoparticles with increasing crystalline nature for higher microwave power is ascertained by X-ray diffraction studies. Previous reports revealed that hexagonally structured ß-Ni(OH)2 was completely transferred into the cubic phase of NiO around 350 °C, confirmed by using thermal analysis (TG/DTA). In our present work, the size and morphology of nanoparticles are ascertained from transmission electron microscopy (TEM) analysis. Flake-like morphology with uniform size, shape and less agglomerated structure formation is obtained for 900 and 600 W of microwave power used for the synthesis of NiO samples. The effect of microwave power used for the synthesis of NiO nanoflakes was analyzed by studying the magnetic and electrochemical behavior of NiO nanoflakes. Room temperature magnetic measurements revealed the small ferromagnetic nature of NiO nanoparticles. It was observed that the samples synthesized at higher microwave power exhibited divergence behavior below 300 K in FC and ZFC measurements, which results superparamagnetic behavior. An enhanced supercapacitor performance with higher specific capacitance values was determined for NiO nanoflake samples synthesized at (25)600 W and 900 W of microwave power.

Synthesis, growth and spectroscopic investigation of an organic molecular charge transfer crystal: 8-hydroxy quinolinium 4-nitrobenzoate 4-nitrobenzoic acid.

An organic intermolecular charge transfer complex salt of 8-Hydroxy quinolinium 4-nitrobenzoate 4-nitrobenzoic acid (OPNB) has been synthesized. Single crystals of OPNB were grown by slow solvent evaporation solution growth technique at room temperature. The (1)H and (13)C NMR spectra were recorded to confirm the molecular structure of the complex salt. The crystal structure of OPNB has been determined by single crystal XRD analysis and it belongs to triclinic crystal system with space group P-1. Fourier transform infrared (FT-IR) spectral study has been carried out to identify the various functional groups present. The UV-Vis-NIR transmittance spectrum was recorded in the range 200-2500nm, to find the suitability of the single crystal for various optical applications. The thermal stability of the crystal was investigated using thermogravimetric (TG) and differential thermal analyses (DTA).

Synthesis, growth, spectral, and thermal studies of a new organic molecular charge transfer complex crystal: 3-nitroaniline 4-methyl benzene sulfonate.

A new organic intermolecular charge transfer complex 3-nitroaniline 4-methyl benzene sulfonate (NATS) has been successfully synthesized and good optical quality single crystals grown by slow solvent evaporation solution growth technique at room temperature using methanol as the solvent. The (1)H and (13)C NMR spectra were recorded to establish the molecular structure of the title complex. The crystal structure of NATS has been determined by single crystal XRD analysis and it belongs to orthorhombic crystal system with space group Pbca. Fourier transform infrared (FT-IR) spectral study has been carried out to confirm the presence of various functional groups present in the complex. Electronic absorption spectrum was recorded to find the prevalent charge transfer activity in the complex. The UV-Vis-NIR transmission spectrum was recorded in the range 200-2500 nm, to find the optical transmittance window and lower cut off wavelength of the title crystal. The thermal stability of the title complex crystal was studied by using thermo-gravimetric and differential thermal analyses and found that the compound is stable up to 215 °C.

Synthesis, growth, structure and spectroscopic characterization of a new organic nonlinear optical hydrogen bonding complex crystal: 3-carboxyl anilinium p-toluene sulfonate.

A new organic nonlinear optical hydrogen bonding complex salt of 3-carboxyl anilinium p-toluene sulfonate has been synthesized and highly transparent good quality single crystals of it were successfully grown employing slow solvent evaporation solution growth technique at ambient temperature. The (1)H and (13)C NMR spectra were recorded to establish the molecular structure. The single crystal XRD analysis carried out reveals that the title salt crystallizes in monoclinic crystal system with non-centrosymmetric P21 space group. The FT-IR spectrum was recorded to confirm the presence of various functional groups in the grown title crystal. The UV-Vis-NIR transmission spectrum was recorded to apprehend the suitability of the single crystal of the title salt for various optical and NLO applications. The TG/DTA thermal analysis was performed to establish the thermal stability of the crystal. The SHG activity in the grown crystal was identified employing the modified Kurtz-Perry powder test. The electronic charge distribution and reactivity of the molecules within the title complex was studied by HOMO and LUMO analysis and the molecular electrostatic potential (MEP) of the title crystal was performed using the B3LYP method.

Growth and characterization of 2-amino-4-picolinium toluene sulfonate single crystal.

2-Amino-4-picolinium toluene sulfonate (2A4PTS), a new organic material, was synthesized and grown as single crystals in room temperature by slow evaporation solution growth technique using water as solvent. The crystal structure of 2A4PTS has been determined using single crystal X-ray diffraction studies. 2A4PTS belongs to monoclinic crystal system. The molecular arrangements in the crystal were studied. The structural perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectral studies have been performed to identify the functional groups. The optical transmittance window and the lower cutoff wavelength of the 2A4PTS have been identified by UV-Vis-NIR studies. The nonlinear optical properties have been investigated by Z-scan method. The nonlinear refractive index and linear absorption coefficient of the 2A4PTS are found to be in the order of 10(-8) cm(2)/W and 10(-4) cm/W, respectively. The laser induced surface damage threshold for the grown crystal was measured using Nd:YAG laser. Thermal analysis carried out on the compound reveals that 2A4PTS is stable up to 133°C. The microhardness test was carried out and the load dependent hardness was measured.