Publication date: 3rd July 2020
Colloidal lead based nanocrystals (NCs) have attracted broad interest for applications in solution-processed voltovoltaic devices.[1] In this presentation, I will discuss several different matierals and approaches for colloidal metal halide, chalcogenide and chalcohalide nanocrystals in energy harvesting and detection devices.
First, I will discuss the room-temperature synthesis of inks based on CsPbBr3 perovskite nanocrystals using short, low boiling-point ligands and environmentally friendly solvents that are easy to process into high quality thin-films.[2]. The robustness of these films is further demonstrated by the fabrication of the first CsPbBr3 NC-based solar cells, with density of short circuit current higher than 6 mA cm-2 and open circuit voltages as high as 1.5 V.
We also explored rectangular-shaped PbS nanosheets with a highly monodisperse thickness of thickness of 1.2 nm.[3] In contrast to rocksalt PbS nanocrystals, these nanosheets have an orthorhombic crystal structure and lack both excitonic absorption features and photoluminescence. The PbS nanosheets are though highly photoconductive in films, with a responsivity up to 0.1 A W–1 and a detectivity of 1.3 × 10^9 Jones and perform significantly beter under bending stress compared to that of films of PbS quantum dots, indicating their use in flexible devices.
Finally we studied a series of surfactant-stabilized lead chalcohalide nanocrystals.[4] The Pb4S3Br2 NCs feature a remarkably narrow size distribution a good size tunability (from 7 to∼ 30 nm), an indirect bandgap, photoconductivity (responsivity= 4±1 mA/W) and stability for months under air. We could also prepare NCs of Pb3S2Cl2 and Pb4S3I2. Although not directly usable for energy harvesting, it highlights the important role of colloidal chemistry in the discovery of new materials otherwise not stable, and motivates further exploration into metal chalcohalides NCs.
[1] Q. A. Akkerman, et al. Nat. mater. 17, 394 (2018)
[2] Q. A. Akkerman, et al.Nature Energy 2, 16194 (2017)
[3] Q. A. Akkerman, et al.Chem. Mater. 2019, 31, 19, 8145–8153
[4] S. Toso, Q. A. Akkerman et al. J. Am. Chem. Soc. 2020, 142, 22, 10198–10211
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