Quantum Nanostructured Dots-in-Host Perovskite Solar Cells

• Autor(a) principal: Alexandre, Miguel Diogo Furtado
• Data de Publicação: 2024
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/169663
• topic: Photovoltaics; Photonics; Intermediate Band Solar Cells; Quantum Dots@Perovskite Solar Cells; k · p Method; Domínio/Área Científica::Engenharia e Tecnologia::Nanotecnologia

The outstanding physical properties of dots-in-host (QD@Host) hetero semiconductors demand detailed methods to fundamentally understand the best routes to optimize their potentialities for different applications. In particular, the application to intermediate band solar cells, closely followed throughout this work. A 4-band k · p-based method was developed for rocksalt quantum dots (QD) that describes the optical properties of arbitrary QD@Host systems. Starting with the construction of the 1-band spherical potential-based analysis of the QD — emulating commonly fabricated colloidal quantum dot. This initial model was then used to determine the intraband transitions and consequent absorption coefficient of the QD system. Remarkably, it was determined that this intraband-only absorption coefficient can reach values close to those of standard bulk semiconductors (104–105 cm−1). The simple 1-band model, was then expanded to a 4-band model that considers interband interactions, thus allowing the calculation of the interband transitions and consequent absorption coefficient. Here, the full model was firstly validated against well-established literature results. The electron transition rate was then determined and its dependency on the main compute parameters analysed. This was followed by a multi-parameter optimization, considering intermediate band solar cells as a promising application, where the best QD configuration was determined, together with the corre- sponding QD@Host absorption spectrum, to attain the theoretical maximum efficiency (∼ 50%) of this photovoltaic technology. These results show the creation of pronounced sub-bandgap absorption due to the electronic transitions from/to the quantum-confined states, enabling a much broader exploitation of the sunlight spectrum. The best-determined QDs were then used as a basis for QD@Host absorber material in complete planar and photonic-enhanced solar cell architectures. In the latter, I explore light management schemes capable of improving light incoupling towards the absorber medium and, in particular, of amplifying the QD-generated absorption via resonant waveguided modes caused by photonic micro-structuring. Here, each device was structurally optimized to maximize the overall optical absorption. The optimized structures revealed significant below-bandgap absorption produced via embedded QDs, without detriments to the above- bandgap absorption mainly occurring in the host perovskite. The gains solely due to the QDs were ∼ 30%, mostly from the increased below-bandgap absorption. Adding the light-trapping (LT) structures managed to further increase the absorption by ∼ 20% (50% total enhancement relative to the pristine cells). Remarkably, while the pristine device photocurrent is below the standard Schockley-Queisser (SQ) limit for single-bandgap cells, as expected, the LT-enhanced QD@Host solar cells managed to surpass this limit by ∼ 40%, underlining the viability of this technology. All in all, this work demonstrated the combined effects of LT and QD-enabled ab- sorption in perovskite materials and devices. Notably, the QDs provided significant below-bandgap absorption, that is further fuelled by the significant photonic-enabled resonance effects from the LT structures. Beyond that, the optical gains achieved here are also predicted to transfer to the electrical domain, thus improving the overall device efficiency.