Defect Passivation via the Incorporation of Tetrapropylammonium Cation Leading to Stability Enhancement in Lead Halide Perovskite

Improving the performances of photovoltaic (PV) devices by suppressing nonradiative energy losses through surface defect passivation and enhancing the stability to the level of standard PV represents one critical challenge for perovskite solar cells. Here, reported are the advantages of introducing a tetrapropylammonium (TPA⁺) cation that combines two key functionalities, namely surface passivation of CH₃NH₃PbI₃ nanocrystals through strong ionic interaction with the surface and bulk passivation via formation of a type I heterostructure that acts as a recombination barrier. As a result, nonencapsulated perovskite devices with only 2 mol% of TPA⁺ achieve power conversion efficiencies over 18.5% with higher V_OC under air mass 1.5G conditions. The devices fabricated retain more than 85% of their initial performances for over 1500 h under ambient conditions (55% RH ± 5%). Furthermore, devices with TPA⁺ also exhibit excellent operational stability by retaining over 85% of the initial performance after 250 h at maximum power point under 1 sun illumination. The effect of incorporation of TPA⁺ on the structural and optoelectronic properties is studied by X‐ray diffraction, ultraviolet–visible absorption spectroscopy, ultraviolet photon–electron spectroscopy, time‐resolved photoluminescence, and scanning electron microscopy imaging. Atomic‐level passivation upon addition of TPA⁺ is elucidated employing 2D solid‐state NMR spectroscopy.     

Growth of low temperature silicon nano-structures for electronic and electrical energy generation applications

This paper represents the lowest growth temperature for silicon nano-wires (SiNWs) via a vapour-liquid–solid method, which has ever been reported in the literature. The nano-wires were grown using plasma-enhanced chemical vapour deposition technique at temperatures as low as 150°C using gallium as the catalyst. This study investigates the structure and the size of the grown silicon nano-structure as functions of growth temperature and catalyst layer thickness. Moreover, the choice of the growth temperature determines the thickness of the catalyst layer to be used.The electrical and optical characteristics of the nano-wires were tested by incorporating them in photovoltaic solar cells, two terminal bistable memory devices and Schottky diode. With further optimisation of the growth parameters, SiNWs, grown by our method, have promising future for incorporation into high performance electronic and optical devices.     

Effect of coating thickness on properties of Mo coatings deposited by plasma spraying

Plasma sprayed molybdenum coatings with different coating thicknesses (100, 200, 300 and 400 μm) were deposited on steel substrate. The variation in microstructural characteristics and properties of coatings with various thicknesses was investigated. The microhardness was measured using a Vickers’ indenter. The quantitative investigation of porosity is carried out with the help of computerised image analyser. The influence of coating thickness on wear resistance was estimated using pin on disc wear test rig. The worn surface of coated pin was characterised by scanning electron microscopy. The experimental results indicated that porosity of coating was increased with increased coating thickness. The enhanced coating thickness also resulted in decreasing microhardness and reduced wear resistance. In this study, the plasma sprayed thin coating with thickness of 100 μm possesses the lowest porosity, the highest hardness and better wear resistance.     

Effect of electron irradiation on the properties of CdTe/CdS solar cells

Polycrystalline CdTe/CdS solar cells are used in space, as well as terrestrial, applications. The results of the studies on the effect of 8 MeV electron irradiation on p-CdTe/n-CdS thin film solar cells prepared by radio frequency (RF) sputtering are presented in this article. Solar cell parameters like short circuit current (I_sc), open circuit voltage (V_oc), fill factor (FF), conversion efficiency (η), saturation current (I_s) and ideality factor (n) have been considered. CdTe thin film solar cells exhibit good stability against electron irradiation up to 100 kGy.     

The effect of precursor concentration on the size of the CdS nanoparticles synthesized in a chicken egg membrane

Results of the studies on the effect of concentration of the precursors on the size of CdS nanoparticles formed in a chicken egg membrane are presented in this article. CdS is formed by the diffusion of aqueous solutions of cadmium acetate and thiourea across the membrane. The optical absorption spectra of the samples exhibit a blue shift in the absorption edge indicating the formation of CdS particles with the size lying in the nanoscale regime. The band gaps of the samples with small reaction times were higher than that of the bulk value, approaching the bulk band gap value with the increase in reaction time for a fixed concentration. Particle sizes were estimated from the band gap values. At lower concentrations, smaller particles are formed even at large reaction times and offer a better control over the size of the particles. At very low concentrations, it takes some time for the absorption edge to evolve after the membrane is removed from the reaction bath. The particle size saturates at higher reaction time possibly due to an equilibrium being established in the system, resulting in stoppage of the diffusion of the reacting ions. Absorption edge could not be detected even days after the removal of the membrane from the reaction bath at still lower concentrations, despite allowing the reaction to take place for large periods of time.     

Morphological changes in nanoparticulate silver films due to electron beam irradiation of polystyrene substrates

Results of the studies on the effect of 8 MeV electron beam irradiation of polystyrene substrates on the morphology of silver particulate films deposited at 455 K in a vacuum of 8 × 10⁻⁶ Torr are reported. Optical absorption studies show the presence of transverse and longitudinal plasmon resonance for films deposited on irradiated polystyrene. Scanning electron microscopy reveals a decrease in particle size with smaller inter-particle separation for irradiated films. Larger clusters are formed in the case of films deposited on polystyrene after 300 h of irradiation. In this paper, we show that the morphology of silver nanoparticulate films can be modified by electron irradiation of inert polymer substrates like polystyrene. The change observed due to irradiation is attributed to the formation of free radicals, thereby altering the polymer-metal interaction.     

Synthesis of Cadmium Sulphide nanoparticles

Nanoparticles form a link between molecular and bulk state of matter and exhibit size dependent physical and chemical properties. A novel technique of synthesizing nanoparticle films on biological membrane substrates is presented here. Cadmium Sulphide (CdS) nanoparticles were prepared by the chemical reaction of aqueous solutions of Cadmium Acetate and Thiourea. The reacting solutions were allowed to diffuse across the membrane for different periods to control the deposition time. The optical absorption spectra of the membrane after the reaction were recorded with bare membrane as reference. The optical absorption spectra show a clear shift in the absorption edge for films with different deposition times at a fixed concentration. The band gaps calculated from the absorption spectra for films with smaller deposition time were higher than that for the bulk CdS. The particle size, estimated from the band gaps, lie in the nanometer range showing that the particle size and band gap can be tailored by controlling the deposition time and concentration of the precursors.     

Effect of mechanical cutting and polishing on the shape memory transformation behavior of NiTi alloy

The results of the studies carried out on the effect of mechanical cutting and polishing on the transformation behavior of Ti-rich NiTi shape memory alloy (SMA) heat-treated at 560 and 660 °C, are presented in this article. Among the samples heat-treated at 560 °C, the sample subjected to mechanical cutting and polishing (HT560MC) shows M → A on reverse phase transformation and A → R → M on forward transformation whereas chemically etched sample (HT560CE) shows the intermediate R-phase both during forward and reverse transformations. Heat treatment at a higher temperature of 660 °C does not facilitate the formation of R-phase in the reverse transformation and helps the formation of R-phase to a very small extent, that too only in HT660MC, during forward transformation due to the reduced dislocation density. Both the heat-treated samples show the effect of mechanical cutting and polishing even at 150th thermal cycling.