Evaluating Pb-based and Pb-free Halide Perovskites for Solar-Cell Applications: A Simulation Study.

Metal halide Pb-based and Pb-free perovskite crystal structures are an essential class of optoelectronic materials due to their significant optoelectronic properties, optical absorption and tuneable emission spectrum properties. However, the most efficient optoelectronic devices were based on the Pb as a monovalent cation, but its toxicity is a significant hurdle for commercial device applications. Thus, replacing the toxic Pb with Pb-free alternatives (such as tin (Sn)) for diverse photovoltaic and optoelectronic applications is essential. Moreover, replacing the volatile methylammonium (MA) with cesium (Cs) leads to the development of an efficient perovskite absorber layer with improved optical & thermal stability and stabilized photoconversion efficiency. This paper discusses the correlation between the experimental and theoretical work for the Pb-based and Pb-free perovskites synthesised using the hot-injection method at different temperatures. Here, simulation is also carried out using the help of SCAPS-1D software to study the effect of various parameters of CsSnI3 and CsPbI3 layers on solar cell performance. This experimental and theoretical comparative study of the Hot-injection method synthesised CsPbI3 and CsSnI3 perovskites is rarely investigated for optoelectronic applications.

Experimental and Theoretical Investigations of MAPbX3 -Based Perovskites (X=Cl, Br, I) for Photovoltaic Applications.

This work mainly focuses on synthesizing and evaluating the efficiency of methylammonium lead halide-based perovskite (MAPbX3 ; X=Cl, Br, I) solar cells. We used the colloidal Hot-injection method (HIM) to synthesize MAPbX3 (X=Cl, Br, I) perovskites using the specific precursors and organic solvents under ambient conditions. We studied the structural, morphological and optical properties of MAPbX3 perovskites using XRD, FESEM, TEM, UV-Vis, PL and TRPL (time-resolved photoluminescence) characterization techniques. The particle size and morphology of these perovskites vary with respect to the halide variation. The MAPbI3 perovskite possesses a low band gap and low carrier lifetime but delivers the highest PCE among other halide perovskite samples, making it a promising candidate for solar cell technology. To further enrich the investigations, the conversion efficiency of the MAPbX3 perovskites has been evaluated through extensive device simulations. Here, the optical constants, band gap energy and carrier lifetime of MAPbX3 were used for simulating three different perovskite solar cells, namely I, Cl or Br halide-based perovskite solar cells. MAPbI3 , MAPbBr3 and MAPbCl3 absorber layer-based devices showed ~13.7 %, 6.9 % and 5.0 % conversion efficiency. The correlation between the experimental and SCAPS simulation data for HIM-synthesized MAPBX3 -based perovskites has been reported for the first time.

Experimental analysis of methylammonium and Formamidinium-based halide perovskite properties for optoelectronic applications.

Nowadays, the toxicity of lead in metal-halide perovskites is the most precarious obstruction in the commercialization of perovskite-based optoelectronic devices. However, Pb-free metal halide perovskites as environment-friendly materials because of their exceptional properties, such as band-gap tunability, narrow emission spectra, low toxicity and easy solution-processability, are potential candidates for optoelectronic applications. Recently, literature reported the poor structural stability and low-emission intensity of Bi-based perovskite NCs. Still, this paper focuses on the fabrication of Formamidinium (FA)-based Bi mixed halide and Methylammonium(MA)-based Bi-pure halide perovskites using Ligand-Assisted Reprecipitation Technique (LARP) technique. XRD diffraction patterns of FA-based perovskites were slightly broad, signifying the nanocrystalline form and limited size of perovskite nanocrystals. While the XRD diffraction patterns of MA3Bi2X9 (X = Cl/Br/I) perovskites were narrow, signifying the amorphous nature and larger size of perovskite nanocrystals. The peak positions were varied in MA-based bismuth halide perovskites with respect to the halide variation from Br to Cl to I ions. The optical study shows the variation in band gap and average lifetime with respect to halide variation leading to enhanced optical properties for device applications. The band-gap of FA3Bi2BrxCl1-x & FA3Bi2IxCl1-x perovskites was calculated to be around 3.7 & 3.8 eV, respectively, while in MA-halide perovskites the band-gap was calculated to be 2.8 eV, 3.1 eV & 3.4 eV with respect to halide variation from I to Cl to Br in perovskite samples using Tauc's plot respectively. Moreover, simulation is carried out using the SCAPS-1D software to study the various parameters in MA & FA-based Bi-pure or mixed halide perovskites. Here, we discussed the variation in efficiency with respect to the thickness variation from 100 to 500 nm for MA3Bi2I9 halide perovskites. These MA3Bi2I9 halide perovskites show minimum efficiency of 4.65 % at 100 nm thickness, while the perovskite sample exhibits maximum efficiency of 10.32 % at 500 nm thickness. Thus, the results stated that the thickness of absorber layers directly affects the device characteristics for optoelectronic applications.

Synthesis and Characterization of Highly Crystalline Bi-Functional Mn-Doped Zn2SiO4 Nanostructures by Low-Cost Sol-Gel Process.

Herein, we demonstrate a process for the synthesis of a highly crystalline bi-functional manganese (Mn)-doped zinc silicate (Zn2SiO4) nanostructures using a low-cost sol-gel route followed by solid state reaction method. Structural and morphological characterizations of Mn-doped Zn2SiO4 with variable doping concentration of 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 wt% were investigated by using X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) techniques. HR-TEM-assisted elemental mapping of the as-grown sample was conducted to confirm the presence of Mn in Zn2SiO4. Photoluminescence (PL) spectra indicated that the Mn-doped Zn2SiO4 nanostructures exhibited strong green emission at 521 nm under 259 nm excitation wavelengths. It was observed that PL intensity increased with the increase of Mn-doping concentration in Zn2SiO4 nanostructures, with no change in emission peak position. Furthermore, magnetism in doped Zn2SiO4 nanostructures was probed by static DC magnetization measurement. The observed photoluminescence and magnetic properties in Mn-doped Zn2SiO4 nanostructures are discussed in terms of structural defect/lattice strain caused by Mn doping and the Jahn-Teller effect. These bi-functional properties of as-synthesized Zn2SiO4 nanostructures provide a new platform for their potential applications towards magneto-optical and spintronic and devices areas.

Charge Transport Properties of Hybrid Nanocomposites Based on Colloidal PbSe Quantum Dots in Poly(2-methoxy,5-(2'-ethylhexyloxy)-P-Phenylenevinylene (MEH-PPV) Matrix.

The synthesis of PbSe nanoparticles were carried out by colloidal route using lead acetate as starting material with Oleic acid/TOP as capping agents at the optimized growth temperature. The phase and surface analysis of oleic acid/TOP capped PbSe nanocrystallites were studied in detail in this article. Current-voltage characteristics of pristine and lead selenide quantum dots (PbSe QDs) incorporated in poly(2-methoxy,5-(2'-ethylhexyloxy)-p-phenylenevinylene (MEH-PPV) thin films have been studied at different temperatures (306-125 K) in hole only device configuration, i.e., ITO/poly(ethylene-dioxythiophene):polystyrenesulphonate (PEDOT:PSS)/MEH-PPV/Au and ITO/PEDOT:PSS/MEH-PPV:PbSe/Au. It has been found that the presence of PbSe QDs in MEH-PPV results in the modulation of the charge transport mechanism from dual conduction mechanism, i.e., trap and mobility model to only trap model. It signifies that the traps are becoming shallower due to reduction in trap density from 2×1017 to 1.2×1017 cm-3 as well as trap energy reduces from 74 meV to 62 meV on the incorporation of PbSe QDs.