Authors: George, Gibu
Source: Universitat de Girona Digital Repository (Universitat de Girona) (article, 2025-04-25)
Field: Materials Science — Materials Chemistry

Computational study and design of materials for photovoltaic applications ENG- The rapid evolution of photovoltaic technologies demands the precise design of materials with tailored properties to overcome performance bottlenecks and achieve high efficiency. This thesis presents a computational investigation into the properties and behavior of molecular systems and materials relevant to photovoltaic applications, with a focus on aromaticity, electronic structure, and defect passivation. By integrating quantum chemical methods and electronic structure analysis, this work explores the interplay between molecular stability, charge transfer dynamics, and defect engineering, offering a multifaceted perspective on material design for energy conversion technologies. The journey begins with indenofluorene (IF)-type systems, where a predictive rule for ground-state stability was established using Clar’s π-sextet theory. This Ground State Stability (GSS) rule provides a robust framework to determine whether IF derivatives favor open-shell singlet or triplet electronic configurations. By extending this approach to π-extended systems like fluorenofluorene and diindenoanthracene, the study demonstrates how molecular aromaticity influences electronic stability and biradical character—essential properties for charge transport in organic photovoltaics. Transitioning from linear to cyclic systems, the thesis investigates carbon nanohoops and their host–guest interactions with fullerenes. Distinct differences between aromatic ([4]DHPP) and antiaromatic ([4]PP) nanohoops reveal how their electronic structures govern charge transfer dynamics, with antiaromatic systems exhibiting ultrafast electron transfer from fullerene to the nanohoop. The effect of stereoisomerism on electronic properties adds another layer of control, showcasing how molecular topology can fine-tune photovoltaic performance. These findings highlight the synergy between molecular design and charge carrier dynamics in organic photovoltaic devices. Finally, the study extends to hybrid perovskites, addressing a key bottleneck: surface defects. Through detailed simulations, the adsorption of fullerenes (C60 and PCBM) on CsPbI3 surfaces was shown to mitigate the detrimental effects of iodine antisite defects, which create trap states. Fullerenes drive surface reconstructions, eliminating these defects, enhancing charge carrier lifetimes, and stabilizing the perovskite interface. These results bridge molecular-scale design with device-scale improvements, illustrating the complementary role of organic and hybrid materials in solar energy conversion. Through the lens of computational analysis, this thesis establishes a cohesive understanding of how molecular and surface-level properties interact to influence material performance in photovoltaic systems. By bridging concepts of aromaticity, charge transfer, and defect passivation, the work provides guiding principles for the rational design of advanced materials, paving the way for improved energy conversion technologies Photovoltaic system ; Antiaromaticity ; Fullerene ; Charge (physics) ; Electronic structure ; Molecular electronics ; Molecular dynamics ; Organic solar cell ; Singlet state Chemical and Physical Properties of Materials ; Advanced Physical and Chemical Molecular Interactions ; Organic Electronics and Photovoltaics