Publication

Compositional Engineering of Perovskite Light Absorbers for Enhanced Stability and Performance through 2D/3D Interfacing

Anwar Qasem M Alanazi
2021
Thèse EPFL
Résumé

The semiconducting hybrid-organic inorganic halide perovskites have excellent optical and electronic properties that attract the interest of scientists and researchers. Perovskite solar cells have seen the most rising-rate in the chart of solar cell efficiency from 3 to over 25% in less than ten years. In the last three years, most researchers have been focusing on the α-FAPbI3-based perovskite solar cells due to having a lower bandgap (1.45 eV) which is closer to the Shockley-Queisser optimum (1.1- 1.4eV) to gain high efficiency. A distinctive feature of FAPbI3 is that it is more thermally stable compared to MAPbI3. However, the α-FAPbI3 perovskite is not stable at room temperature as it converts to the undesirable Ύ-phase. The 2D- Ruddlesden-Popper-phase-doped 3D FAPbI3 enhancing the stability of the structure, albeit the bandgap is increased rendering a less optimal bandgap. The main achievement of this thesis is discovering that the doping of FAPbI3 with large alkyl ammonium moieties enhances efficiency and stability while maintaining the bandgap of pure α-FAPbI3 perovskite phase. I describe the resulting composition by the formula (A)xFAPbI3, where A represents the large alkyl ammonium iodide species. I study the stabilization of α-FAPbI3 via doping with 5-amino valeric acid hydroiodide (AVAI). By using solid-state NMR, we demonstrate the atomic-level interaction between this molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. Optical measurements confirm that there is no effect on the bandgap of FAPbI3 after doping. The devices based on (AVAI)0.25FAPbI3 exhibit superior operational stability in comparison with neat FAPbI3 while achieving power conversion efficiency of 19%. A similar approach based on benzylammonium iodide (BzI) has been used. The structural and optical characterization of films based on (BzI)xFAPbI3 composition demonstrate that there is no 2D phase forming under these conditions. Moreover, solid-state NMR results show BzI interacting on the atomic level with α-FAPbI3 by binding to the 3D perovskite through hydrogen bonding interaction and stabilizing it against the detrimental α-to-Ύ phase transition. Perovskite solar cells based on the (BzI)0.25FAPbI3composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions.Finally, films based on (BzI)0.25FAPbI3 compositions are further investigated upon aging under the ambient conditions, as they show an unexpected transition from black to red color without transition to expected yellow Ύ phase, unlike the reference FAPbI3. I perform different measurements to investigate the nature of this red phase as a function of annealing temperature compare these properties to the corresponding Ruddlesden-Popper phase (Bz2FAn-1PbnI3n+1). The red phase was found to be a mixture of a 2D phase (n = 2) Bz2FAPb2I7 and Ύ-FAPbI3, which acts as a barrier to the α-to-Ύ phase transition.

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Cellule photovoltaïque à pérovskite
Une cellule photovoltaïque à pérovskite est un type de cellule photovoltaïque dont la couche active est constituée d'un matériau de formule générale à structure pérovskite dans laquelle A est un cation, généralement de méthylammonium (MA), de formamidinium ou de césium , B est un cation d'étain ou de plomb , et X est un anion halogénure tel que chlorure , bromure ou iodure . Le rendement des cellules photovoltaïques utilisant ces matériaux est en constante augmentation depuis la fin des années 2000.
Rendement d'une cellule photovoltaïque
vignette| Meilleurs rendements de différentes technologies de cellules photovoltaïques mesurés en laboratoire depuis 1976. Le rendement d'une cellule photovoltaïque, parfois noté η, est le rapport entre l'énergie électrique générée par effet photovoltaïque d'une part et l'énergie électromagnétique reçue par la cellule photovoltaïque sous forme de rayonnement solaire d'autre part. Avec la latitude et le climat du lieu d'installation, le rendement des cellules solaires d'un dispositif photovoltaïque détermine la production d'énergie électrique annuelle du système.
Cellule photovoltaïque
Une cellule photovoltaïque, ou cellule solaire, est un composant électronique qui, exposé à la lumière, produit de l’électricité grâce à l’effet photovoltaïque. La puissance électrique obtenue est proportionnelle à la puissance lumineuse incidente et elle dépend du rendement de la cellule. Celle-ci délivre une tension continue et un courant la traverse dès qu'elle est connectée à une charge électrique (en général un onduleur, parfois une simple batterie électrique).
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