Black-Yellow Bandgap Trade-off during Thermal Stability Tests in Low-Temperature Eu-doped CsPbI3

Salvatore Valastro^a^,^c, Giovanni Mannino^a, Emanuele Smecca^a, Corrado Bongiorno^a, Salvatore Sanzaro^a, Ioannis Deretzis^a, Antonino La Magna^a, Ajay Jena^b, Tsutomu Miyasaka^b, Alessandra Alberti^a

^aInstitute for Microelectronics and Microsystems (CNR-IMM), Zona Industriale - VIII Strada 5, Catania 95121, Italy

^bToin University of Yokohama, Graduate School of Engineering, 1614 Kuroganecho, Aoba, Yokohama, 225-8503, Japan

^cDipartimento di Scienze Chimiche, Università degli Studi di Catania, V.le A.Doria 6 95125 Catania

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)

València, Spain, 2022 May 19th - 25th

Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson

Contributed talk, Salvatore Valastro, presentation 035
DOI: https://doi.org/10.29363/nanoge.hopv.2022.035
Publication date: 20th April 2022

The black g-phase of CsPbI₃ with its bandgap at ~1.75eV can enable the take-off of tandem solar cells as soon as its intrinsic instability to the yellow d-phase is solved. Here, a black g-phase is formed at low temperature (80-90 °C) by incorporating Eu through EuCl₃ or EuI₂[1],[2]. It is forced to become yellow by thermal heating under nitrogen. It is demonstrated how Spectroscopic Ellipsometry measurements and the related critical points analysis provide a newly-conceived diagnostic tool to monitor the transformation through the Bandgap footprint. As two sides of the same coin, the consumption of the black g-phase and the growth of the yellow d-phase are addressed and modelled in the temperature range 60-100 °C using the Avrami’s theory. This approach allows extracting the activation energies of the phase transformation that are 0.95 eV vs. 1.15 eV using EuI₂ and EuCl₃, respectively. In-situ Transmission Electron Microscopy analyses combined with Fast Marching simulations highlight that the phase transformation occurs through constant nucleation and growth. Europium has indeed the capability to tackle those processes and to extend the durability of the black g-phase at 30 °C in N₂ to ~250 days, hugely above the one observed without Eu (~hours) [3].

References:

[1] Jena, A.K.; Kulkarni, A.; Sanehira, Y.; Ikegami, M.; Miyasaka,T. Stabilization of α-CsPbI3 in Ambient Room Temperature Conditions by Incorporating Eu into CsPbI3 Chemistry of Materials 2018, 30 (19), 6668-6674

[2] Alberti, A., Smecca, E., Deretzis, I., Mannino, G., Bongiorno, C., Valastro, S., Sanzaro, S., Fisicaro, G., Jena, A.K., Numata, Y., Guo, Z., Spinella, C., Miyasaka, T., La Magna, A. Formation of CsPbI3 γ-Phase at 80 °C by Europium-Assisted Snowplow Effect. Adv. Energy Sustainability Res. 2021, 2: 2100091.

[3] Valastro, S.; Mannino, G.; Smecca, E., Bongiorno, C., ,Sanzaro, S.,Deretzis, I., La Magna, A. , Jena, A.K., Miyasaka, T., Alberti, A. Black-Yellow Bandgap Trade-off during Thermal Stability Tests in Low-Temperature Eu-doped CsPbI3 Sol. RRL 2022 (Just Accepted)

Acknowledgements:

This activity was partially supported at CNR by the national projects BEYOND NANO Upgrade (CUP G66J17000350007) and VertiGrow (CUP B15F21004410005).

CNR also acknowledges the project PON entitled “Tecnologia per celle solari bifacciali ad alta Efficienza a 4 terminali per utility scale”, called BEST-4U, financed by the Italian Ministry MIUR (CUP B88D19000160005)

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