All inorganic Tin Germanium Perovskite Nanocubes: Towards Highly Efficient Lead free Perovskite Nanocrystals based Solar Cells
Paola Vivo a, Maning Liu a, Hannu Pasanen a, Harri Ali-Löytty b, Kimmo Lahtonen c, Syeda Qudsia d, Jan-Henrik Smått d, Mika Valden b, Nikolai V. Tkachenko a
a Tampere University of Technology, Finland, Tampere, Finland
b Tampere University of Technology, Finland, Tampere, Finland
c Tampere University of Technology, Finland, Tampere, Finland
d Åbo Akademi University, Finland, Porthaninkatu, 3, Turku, Finland
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#NCFun19. Fundamental Processes in Semiconductor Nanocrystals
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Ivan Infante and Jonathan Owen
Poster, Paola Vivo, 444
Publication date: 18th July 2019

Colloidal perovskite nanocrystals have been recently widely investigated as promising candidates for the next-generation of optoelectronic devices including photovoltaics, light-emitting diodes, photodetectors, and lasers, because of their facile synthesis and their outstanding and size-tunable optoelectronic properties. Similarly as for the bulk perovskite counterparts, there are several bottlenecks impeding the widespread commercialization of perovskite nanocrystals, namely the toxicity of lead, key constituent of the most efficient halide perovskite materials, and their mediocre intrinsic stability.1,2
The most promising lead-free perovskite materials rely on tin (Sn), being it the closest analogue to lead, yet showing highly unstable characteristic due to the rapid oxidation from Sn2+ to Sn4+ in ambient conditions.3 One effective strategy to address instability of Sn is its mixing with other relatively air-stable metals such as germanium (Ge), as recently demonstrated in bulk perovskite films.4 In this work, we pioneer the synthesis of all-inorganic Sn-Ge perovskite nanocubes, and we provide evidence of Ge2+ stabilizing Sn2+ cation, while at the same time enhancing the nanocrystals optical and photophysical properties. In fact, the excitonic lifetime of Sn-Ge based nanocrystals is significantly prolonged compared to that of Ge-free based nanocrystals and the photoluminescence quantum yield greatly increased. This is mainly attributed to Ge’s role in filling the high density of Sn vacancies and reducing the surface trap states. As light harvesters in solar cells, Sn-Ge nanocrystals lead to devices with power conversion efficiencies as high as 4.7%, which is one of the highest records among lead-free perovskite nanocrystals solar cells.
References
1. Li, Y. et al. Advances in metal halide perovskite nanocrystals: Synthetic strategies, growth mechanisms, and optoelectronic applications. Mater. Today 2019, in press.
2. Liu, M. et al. Halide Perovskite Nanocrystals for Next‐Generation Optoelectronics. Small 2019, 15, 1900801.
3. Ke, W.; Kanatzidis, M.G. Prospects for low-toxicity lead-free perovskite solar cells. Nat. Commun. 2019, 10, 965.
4. Chen, M. et al. Highly stable and efficient all-inorganic lead-free perovskite solar cells with native-oxide passivation. Nat. Commun. 2019, 10, 16.

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