A-site Modified Hybrid Perovskites: Compositional Engineering and Role of Grain Boundaries on Optoelectronic Properties (ASTRAL)

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Hybrid lead iodide perovskites based on a mixture of A-site cations have attracted significant attention due to their higher stability when compared to the parent compound methyl ammonium lead triiodide. The objectives of this project center around fundamental understanding of formability, crystallization and grain boundary engineering in solution-processed A-site modified hybrid alkyl ammonium lead iodide perovskites. Through an integrated synthesis, processing and computational effort, functional perovskite inks with optimal crystal size and solvent chemistry will be developed to examine the optoelectronic properties of solid-state absorber films in device structures. In order to understand the synergistic effect of multi-cation hybrid perovskite structures, detailed information on the role and position of the different A-site cations and crystal symmetry is critically important. Owing to the chemical and structural degrees of freedom, we propose to systematically vary the substitution of A-site cations, which are majorly responsible for the structural parameters (tolerance factor) and modulations in optical band gap The research tasks in this project will primarily focus on (i) formulation of perovskite inks based on A-site modified chemical compositions ((A1,A2,A3,A4)PbI3) in conjunction with solution studies to develop synthetic protocols for controlled crystal growth and test new solvent systems for precise crystal engineering (ii) control of on-surface grain growth and tailoring of grain boundaries in single and tandem application methods (spin-coating and electrospraying) (iii) fabrication of perovskite solid-state absorber films to investigate the transport properties as function of the size of perovskite domains (iv) detailed understanding of perovskite materials, their composition, nucleation and layer growth and effects of intergranular and intragranular transport mechanisms in predevice structures (v) demonstrate the impact of A-site engineering in mixed-cation perovskites by validating the experimental data through DFT calculations and (vi) fabricate thin film solar cell device structures and evaluation of the solvent influence, deposition technique and processing conditions on the device performance and stability. Preliminary studies on degradation of pre-device structures through light or heat-stimulated processes will be initiated as well. In summary, this interdisciplinary effort will pursue an integrated synthesis – application – modelling approach to gather new insights in the nucleation behavior of perovskite crystals with A-site variations and in-situ studies on solvent effects to obtain stable and processable inks, film formation and understanding of pre-device structure towards optical and transport properties that will be validated by DFT calculations on defect chemistry of A-site mixed systems and modelling of grain boundary transport.