Advances in Methylammonium Lead Halide Perovskites Synthesis, Structural, Optical, and Photovoltaic Insights

Introduction

Methylammonium lead halide perovskites, namely MAPbX3 (X = Cl, Br, I), have demonstrated potential as hybrid organic-inorganic perovskites in solar cell technology ¹. Perovskites provide appealing features such as extended carrier lifetimes, adjustable band gaps, strong absorption coefficients, and convenient synthesis processes that can be carried out using solutions. The optoelectronic characteristics of solar cells have led to a substantial increase in their power conversion efficiency (PCE), hence improving their competitiveness compared to traditional silicon-based cells. The perovskites MAPbX3 have an ABX3 crystal structure, where X represents a halogen ion (Cl, Br, or I), B represents a smaller divalent cation (often lead), and A represents a larger monovalent cation (such as methylammonium, MA+). By altering the composition of the A, B, or X sites, the flexibility of this structure allows for the adjustment of several properties, including the band gap, absorption characteristics, and lattice parameters³. The Hot-Injection Method (HIM) synthesis of MAPbX3 allows for the cost-effective and non-vacuum-based production of perovskites with distinct structural, morphological, and optical properties. This study aims to investigate the correlation between the structural characteristics of solar cells and their photovoltaic efficiency. It utilizes experimental research and device simulations to examine these attributes and their impact on the performance of solar cells. This study aims to provide a comprehensive understanding of the potential of MAPbX3 perovskites for solar cell applications by utilizing photovoltaic simulations to evaluate their structural, optical, and morphological features⁴. The outcomes have the potential to guide future advancements in perovskite solar cell technology, hence promoting the development of more cost-effective and efficient solar energy alternatives⁵.

Experimental Methods

Methylammonium lead halide perovskites (MAPbX₃; X = Cl, Br, I) are synthesised using a number of important precursors to produce each variation. Lead salts, with 99.99% trace metals foundation, include lead(II) bromide (PbBr₂), lead(II) iodide (PbI₂), and lead(II) chloride (PbCl₂). The organic component is further made up of methylammonium halides, which include methylammonium iodide (MAI), methylammonium bromide (MABr), and methylammonium chloride (MACl), all of which are more than 99% pure. Important components of the solution chemistry, the solvents octadecene (ODE), oleyl-amine (OLA), and oleic acid (OA) stabilize the perovskites throughout production. Other compounds are also used especially in the manufacture of MAPbI₃, including tri-octyl phosphine (TOP). Consistency and purity in the produced perovskites are ensured by the usage of all chemicals, which are obtained from Sigma Aldrich and utilized directly ⁶.

The actual synthesis method is based on the controlled Hot-Injection Method (HIM). In a three-neck round-bottom flask (RBF), 1 mM of MAI is dissolved in 3 mL of OA and well swirled. The solution is next rapidly injected with 0.5 mM PbI2 dissolved in TOP after being heated to 100°C in an argon atmosphere until clear. Following a ten-minute period at 195°C, the solution is chilled, centrifuged, and toluene-washed to produce MAPbI₃. With 1 mM of MABr dissolved in a mixture of OA and ODE and PbBr₂ in the same mixture, the synthesis of MAPbBr₃ proceeds similarly⁷. The remainder of the process is 200°C, same as with MAPbI3. The MAPbCl3 synthesis is repeated at 180°C, with 1 mM of MACl dissolved in the solution and PbCl₂ in an ODE and OLA mixture⁸.

Results and Discussion

The structural, optical, and morphological characteristics of the MAPbX₃ perovskites (X = Cl, Br, I) are evaluated through a thorough characterization process following their synthesis. Various techniques are employed to examine the properties of these perovskites⁹. X-ray diffraction (XRD) technique analyzes the crystalline structure, revealing information about each perovskite’s phase, size, and lattice planes ¹⁰.

Figure 1: XRD pattern of MAPbBr3, MAPbI3 and MAPbCl3. Click here to View Figure

Figure 2: SEM diagram of MAPbI3, MAPbBr3 and MAPbCl3 7. Click here to View Figure

The diffraction patterns show that MAPbBr₃ and MAPbCl₃ crystallize in a cubic phase, while MAPbI₃ adopts a tetragonal phase ¹¹. The crystallite sizes range from 25.77 to 38.75 nm, with lattice strains correlating with optical and photovoltaic properties. Field Emission Scanning Electron Microscopy (FE-SEM) imaging method provides insights into the surface morphology of each perovskite ¹². It captures particle shapes and distributions, revealing morphological variations between halide variants ¹³.

For instance, MAPbI₃ forms a mixture of rods and spherical nanocrystals, while MAPbCl₃ shows cubic nanocrystals, with particle sizes ranging from 31.1 to 44.5 nm, in close agreement with the crystallite sizes calculated from XRD ¹⁴. Transmission Electron Microscopy (TEM) technique provides high-resolution images of the perovskite particles, enabling a nanoscale analysis of their size and distribution. The particle size distribution can be computed from these images ¹⁵.

Figure 3: Blue shifting in absorption band edge of MAPbI3, MAPbBr3 and MAPbCl3. Click here to View Figure

UV-Vis Spectroscopy This technique observes the absorption spectra of the perovskites, revealing band gaps and absorption coefficients ¹⁶. The band gaps range from 1.56 to 3 eV, showing a blue shift in the absorption band edge from MAPbI₃ to MAPbCl₃. Photoluminescence (PL) investigations provide the emission spectra of the perovskites, showing broad peaks in the 400–800 nm range, with blue shift emission from I through Br to Cl. Time-Resolved PL (TRPL) studies show carrier lifetimes of 1.72 ns (MAPbI₃), 1.87 ns (MAPbBr₃), and 7.65 ns (MAPbCl₃), indicating MAPbCl₃ has the longest charge separation.SCAPS-1D simulations show that MAPbI₃ yields a PCE of 13.66% at 250 nm thickness, while MAPbBr₃ and MAPbCl₃ yield 6.87% and 4.98% at 500 nm thickness, respectively ¹⁷. The combination of band gap, carrier lifetimes, and photovoltaic efficiency positions MAPbI₃ as the most promising candidate for solar cells. Analysis and refinement of X-ray diffraction data (Analytical Technologies, India) using NetworkX Python library.

Figure 4: SCAPS – 1D Simulated PCE of Perovskite Materials (MAPbX3, X = Cl, I and Br) at different thicknesses. Click here to View Figure

Conclusion

This study examines the potential application of methylaminium lead halide perovskites (MAPbX3) in solar cell technology. The perovskites form distinct phases, with MAPbI3 adopting a tetragonal morphology, while MAPbBr3 and MAPbCl3 have a cubic structure. The lattice strains are directly related to the optical and photovoltaic properties. The diameters of the crystallites vary between 25.77 and 38.75 nm. Halide variants reveal distinct morphological variations; MAPbI3 takes the shape of elongated rods and spherical nanocrystals, MAPbCl3 showcases cubic nanocrystals, and MAPbBr3 demonstrates granular structures. The UV-Vis spectroscopy revealed a blue shift in the absorption band boundaries when transitioning from MAPbI3 to MAPbCl3. The TRPL studies revealed carrier durations ranging from 1.72 to 7.65 ns, indicating that MAPbCl3 has the most extended charge separation. MAPbBr3 and MAPbCl3 exhibited photovoltaic performance of 6.87% and 4.98%, respectively, when their thickness was 250 nm. The study highlights the need of employing non-vacuum synthesis techniques, specifically the Hot-Injection Method (HIM), for cost-effective manufacturing of perovskites.

Acknowledgments

We acknowledge the support of Department of Physics and CIF Lab, Kalinga University, Naya Raipur (CG) India.

Conflict of Interest

The authors conducted ethical and transparent research, demonstrating the importance of ethical practices in scientific research.

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