Seryio Saris
The development of sustainable, renewable and economic chemical processes lies in the centre of todayâs global energy challenge. Like in plants, artificial photosynthesis offers an auspicious solution in harvesting solar energy and storing it in chemical bonds. A number of potential architectures and material systems have been proposed. Among these, the construction of light harvesting antennas funnelling energy towards a catalytic center is a promising idea that mimics the natural photosynthetic system.
Semiconductor nanocrystals (NCs) and plasmonic metal NCs are ideal candidates to develop such a concept. The former possesses a tunability of optical properties which is superior to other light absorbers. The latter are interesting photocatalysts able to steer reaction selectivities in a unique way related to their plasmon decay. Among semiconductor NCs, the recently emerged lead halide perovskite NCs represent ideal FRET-type donors due to their high quantum yields and short photoluminescence lifetimes. Yet, incorporating them into a multicomponent light harvesting assemblies is challenging due to their inherent instability issues in conditions which are normally used to drive water splitting or CO2 reduction.
Hence, this thesis focuses on exploring the viability of a photocatalytic assembly including perovskite and metal NCs, starting from enhancing the environmental stability of perovskite NC films, then moving towards investigating the optical and structural changes resulting from their interfacing with plasmonic metal NCs, and finally demonstrating an exemplary assembly platform to study energy transfer between perovskite and metal NCs that ultimately reveals improved photocatalytic efficiencies compared to the single components.
Firstly, the fabrication of CsPbX3 NC aluminium oxide (AlOx) nanocomposites by a low temperature atomic layer deposition (ALD) process is proposed as a novel protection scheme. The nucleation and growth of AlOx on the NC surface was investigated by a miscellanea of techniques, highlighting the importance of the interaction between the ALD precursors and the NC surface to uniformly coat the film. These nanocomposites show enhanced stability under exposure in air, irradiation, heat, and upon immersion in water for 1 hour.
A deeper understanding of the perovskiteâmetal chemistry is crucial to elucidate the instability problems at the assembly and device level. In the second part, we study the reactions occurring between CsPbX3 (X = Br, BrI, I) perovskite and plasmonic metals (M = Ag, Cu, Au) NCs. We demonstrate a fast optical and structural degradation of perovskites, particularly of iodine containing analogs, driven by the formation of metal halides.
While the encapsulation of perovskite NCs in inorganic matrices has been shown to be effective in enhancing their stability, the feasibility of extracting electronic energy from these composite systems still needs to be studied. In this final part, we explore the capacity of CsPbBr3 NC/AlOx nanocomposite films to drive chemical reactions by coupling them to plasmonic Ag NCs. AlOx is used both as a stabilizing layer and as a spacer to study distance-dependent energy transfer, which reveals a migration of energy from the perovskite toward the AgNCs. We then utilize this pooled energy for a plasmon-mediated dye desorption where we demonstrate enhancement effects of spectral and spatial absorption on the reaction outcome due to the coupling to perovskites NCs.
EPFL2020
