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
a Institute for Microelectronics and Microsystems (CNR-IMM), Zona Industriale - VIII Strada 5, Catania 95121, Italy
b Toin University of Yokohama, Graduate School of Engineering, 1614 Kuroganecho, Aoba, Yokohama, 225-8503, Japan
c Dipartimento 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
Poster, Salvatore Valastro, 285
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].

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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