Venkatraman Madurai Ramakrishnan

Bismuth is one of the promising elements that can replace toxic lead in perovskite solar cells. However, surface roughness and inhomogeneous morphology with voids on the bismuth perovskite films limits their photovoltaic performance. In the present work, a scalable doctor-blade technique is employed to prepare perovskite thin film with high surface coverage. Methylammonium bismuth halide (MABiH) ((CH₃NH₃)₃Bi₂Cl_xI_9-x) nanoparticles were synthesized by conventional sol-gel technique. The formation of perovskite structure was confirmed by X-ray diffraction measurement which confirmed that MABiH perovskite films were in hexagonal symmetry with polycrystalline nature. The prepared perovskite nanoparticles were deposited on mesoporous TiO₂-coated FTO substrates through the spin coating technique and doctor blade method. Morphology analysis of MABiH perovskite revealed the formation of an orange Lily-like structure with higher surface coverage. Lead-free mesoporous perovskite solar cells prepared using MABiH perovskite material with carbon as hole extraction layer showed a maximum power conversion efficiency (PCE) of 0.004 %, with short circuit current density of 89 μA/cm², open circuit voltage of 0.12 V and fill factor of 38 %. These results allow us to step toward fabricating bulk MABiH lead-free perovskite solar cells.

This research work aims to develop a new dual-functional electrode material suitable for both lithium-ion batteries (LIBs) and dye-sensitized solar cells (DSSCs). Nanostructured Cu₂ZnSnS₄ (CZTS) was synthesized through the solvothermal method. Structural properties analysed through the X-ray diffraction pattern (XRD) and Raman spectra reveal the formation of the CZTS with kesterite structure . The stoichiometry and the oxidation states of CZTS have been analyzed using X-ray photoelectron spectroscopy (XPS). The core level XPS spectra of Cu 2p, Zn 2p, Sn 3d, and S 2p confirm the presence of the constituent elements in the required oxidation states (Cu⁺, Zn²⁺, Sn⁴⁺, S²⁻). The surface morphology of the CZTS nanoparticles showed a nanoflake-like structure with a surface area of 34.20 m² g⁻¹. The geometrical optimization, electronic, and optical properties were calculated using DFT calculations. The semiconducting material CZTS is electrochemically active toward Li, which can be used as an alternative anode material for lithium-ion batteries offering potential improvements in cycling stability and specific capacity. The electrochemical studies of the CZTS nanoflakes exhibited a specific capacity of 1141.08 mA h g⁻¹ and 350 mA h g⁻¹ at 0.1C and 1C rates respectively. The cycling stability of CZTS at a high scan rate of 1C, and the specific capacity of 220 mA h g⁻¹ over 70 cycles with 73% coulombic efficiency, suggest it to be a promising alternative anode material in the next-generation lithium-ion batteries. The performance of CZTS as a counter electrode in dye-sensitized solar cells was also explored. The DSSC constructed with CZTS as the counter electrode showed an efficiency of 5.9%.

Summary: By the process of doping in semiconducting nanomaterials, properties of the materials such as electronic, optical and photochemical properties can be effectively tuned. Here fluorine doped TiO₂ nanostructures were synthesized by microwave assisted solvothermal technique. The X‐ray diffraction patterns (XRD) and Raman analysis results of the sample exhibits peaks characteristic of anatase TiO₂. From the UV‐visible absorption analysis, an increase in visible light absorption with no significant change in the absorption edge was noticed. F doped TiO₂ nanostructures were found to possess quasi cubic morphology through the transmission electron microscope images and from the presence of well‐defined ring pattern in selected area electron diffraction patterns the polycrystalline nature of the samples were confirmed. The presence of fluorine in the TiO₂ lattice was confirmed through the presence of Ti³⁺ states using X‐ray photoelectron spectroscopy (XPS) analysis and electron paramagnetic resonance (EPR) analysis respectively. The prepared TiO₂, F doped TiO₂ nanostructures were coated over fluorine doped tin oxide (FTO) substrates, further they were subjected to dye sensitization and were used as photoanodes in dye sensitized solar cells and their power conversion efficiencies were studied.