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Stable Halide Perovskite Nanocrystals for Efficient Optoelectronic Devices

Periodic Reporting for period 1 - StabPerov (Stable Halide Perovskite Nanocrystals for Efficient Optoelectronic Devices)

Reporting period: 2019-08-01 to 2021-07-31

The increasing demand for clean and renewable energy requires the development of improved strategies and materials to obtain energy from renewable sources. Improved efficiencies for solar cells, photocatalytic CO2 reduction and water splitting are highly investigated, but also more efficient ways to use electrical energy for lighting must be developed. These challenges are also recognized by the European Energy Efficiency Plan.

Perovskites have shown impressively high efficiencies for solar cells and light emitting diodes but stability issues are still a big problem, which currently hinders the wider commercialization and the fabrication of perovskite based devices.

The StabPerov project succeeded in developing strategies for the synthesis of highly stable perovskites by using amphiphilic molecules as coating materials and contributed to the structural and optical characterization of these nanocrystals.
The StabPerov project contributed to two of the most challenging aspects in perovskite nanoparticle preparation, namely stability issues and the understanding of the formation of perovskite nanocrystals. In order to achieve such goals, we have developed new synthetic routes and investigated the nanocrystal formation via live photoluminescence (PL) detection.

To obtain stable perovskite nanocrystals (NCs), a new method was developed to obtain spontaneous crystallization perovskite NCs in nonpolar organic media by mixing of precursor–ligand complexes. The shape of the NCs can be tuned from nanocubes to nanoplatelets by decreasing the ratio between the monovalent cation (e.g. formamidinium (FA+) and Cs+) to divalent Pb2+ precursors. What’s more, the perovskite nanorods with improved stability were directly synthesised by controlling and fine-tuning the concentration and ratio of organic ligands (FA and oleate) and/or the ligand/precursor ratio (oleic acid/PbI2). Furthermore, we could demonstrate that the emission properties of perovskite nanorods can be fine-tuned by controlled halide exchange.

State-of-the-art structural and optical spectroscopy methods and techniques were employed for sample characterization of the nanocrystals and to analyse NC formation during synthesis. As an example, a new setup for in-situ PL detection was developed to monitor the progress of CsPbBr3 synthesis during nanocrystals growth, sample cooling, and purification. As an intriguing result, we observed that nanocrystals would form superstructures during the process of cooling in dispersion (which was frequently ignored in the literature). Furthermore, the FAPbI3 NCs were further characterized by femtosecond pump–probe spectroscopy in combination with density functional theory calculations, revealing that Bromium–based perovskite NCs display a superior stability over Iodine–based perovskite NCs.
This project has tackled two of the most challenging aspects in perovskite nanoparticle preparation, namely stability issues and the understanding of the formation of perovskite nanocrystals. The outcome of the project directly contributes to a better understanding of the formation of perovskites. These findings could potentially pave the way towards the commercialization of perovskite nanocrystals based devices.

The achievements made in this project resulted in six high impact publications in internationally renowned peer-reviewed journals.

The results of the project were disseminated to the research community in three international conferences and to the non-scientific community at public events such as University Open days for high school students.