Developing highly stable halide perovskite for solar cells and photodetectors

Lead halide perovskite, 3D cubic AM(ll)X3, have garnered significant attention due to their exceptional optoelectronic properties, enabling applications in solar cells, light-emitting diodes, and photodetector applications. However, concerns over lead toxicity and environmental pollution necessitate the development of lead-free alternatives. All-inorganic (i) A3M(lll)2X9 2D-layered halide perovskite (2D-LHP), (ii) A2M(l)M(lll)X6 3D-cubic double halide perovskite (3D-cDHP), and (iii) A4M(ll)M(lll)2X12 layered-double perovskite (LDHP) are emerging as promising materials due to their superior stability under light, heat, and atmospheric conditions compared to organic-inorganic halide perovskites. However, their optical and electronic properties,

especially in relation to photovoltaic, light emitting and photodetector applications, require further exploration and optimization. This proposal focuses on leveraging alloying and sublattice distortion in 3D-cDHP and LDHP as a strategy to tailor their optoelectronic properties. Specifically, we aim to investigate the effects of substituting M(I) (Ag+, Na+, Cu+) and M(III) (Bi3+, Sb3+, ln3+) sites in the A2M(l)M(lll)X6 structure, and M(II) (Cu2+, Mn2+, Cd2+) and M(III) (Sb3+, Bi3+) sites in A4M(ll)M(lll)2X12 structure with Cs+ and Rb+ as the preferred A-site cation, and Br- and I- as halide anions. This approach capitalizes on the isoelectronic nature of these cations with Pb2+, allowing for structural stability while introducing unique optical and electrical properties. Recent studies suggest that alloying in double perovskites induces local symmetry changes and distortions in the MX6 octahedra [1-3]. These distortions, driven by Jahn-Teller effects, break inversion symmetry and deactivate parity-forbidden transitions, enabling enhanced excitonic recombination. Furthermore, sublattice distortions reduce the optical bandgap, offering new opportunities for bandgap engineering. These changes are expected to result in materials with improved light absorption and emission properties, making them highly suitable for photovoltaic and optoelectronic

devices.

Our proposed research will focus on the following objectives:

1. We will synthesize alloyed double perovskites with compositions

(A2M(l)M(lll)X6 and A4M(ll)M(lll)2X12 ) using solution-based thin film methods, viz, spin coating process and thermal evaporation technique. Structural characterization will involve X-ray diffraction, Raman spectroscopy and electron microscopy and spectroscopy techniques to confirm crystal phases and identify local distortions.

2. We will employ UV-Vis spectroscopy, photoluminescence (PL), and time-resolved PL to study bandgap evolution and excitonic behavior. Carrier mobility and conductivity will be analyzed using Hall effect measurements and impedance spectroscopy.

3. Optimized double perovskites will be integrated into photovoltaic and photodetector devices. Device performance, including power conversion efficiency (PCE) and

external quantum efficiency (EQE), and photodetector performances will be evaluated under standard test conditions. By systematically exploring the interplay between cationic alloying, sublattice distortion, and optoelectronic performance in cubic and layered double perovksite, this research aims to establish design principles for next-generation lead-free perovskites. The resulting materials are expected to achieve higher efficiency and stability, and sensitivity paving the way for sustainable and scalable applications in solar energy and sensing. In summary, this proposal seeks to address critical challenges in double perovskite research by advancing our understanding of alloying-enabled sublattice distortions. The outcomes will contribute significantly to the development of environmentally friendly, high-performance optoelectronic devices.