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S-I1
S-I2
Maria Antonietta Loi studied physics at the University of Cagliari in Italy where she received the PhD in 2001. In the same year she joined the Linz Institute for Organic Solar cells, of the University of Linz, Austria as a post doctoral fellow. Later she worked as researcher at the Institute for Nanostructured Materials of the Italian National Research Council in Bologna Italy. In 2006 she became assistant professor and Rosalind Franklin Fellow at the Zernike Institute for Advanced Materials of the University of Groningen, The Netherlands. She is now full professor in the same institution and chair of the Photophysics and OptoElectronics group. She has published more than 130 peer review articles in photophysics and optoelectronics of nanomaterials. In 2012 she has received an ERC starting grant.
Tin-based perovskites have long remained an unexplored subclass of materials in the metal halide perovskite field. The recent efficiency improvement in thin film solar cells [1] and the observation of a long hot carrier cooling time in forma-midinium tin iodide (FASnI3) [2], stimulated not only the attention of the community but also the awareness that understanding of the material's
properties become a pressing matter if further improvements in device performance are desired. Since pronounced background doping can easily obscure the actual material properties, it is of paramount
importance to understand how different processing conditions affect the observed behavior.
Using photoluminescence spectroscopy, we investigated thin films of FASnI3 fabricated through different protocols [3]. We show that the best quality material, as marked by the photophysical properties is obtained by the addition of small amounts of 2-phenylethylammonium (PEA) ions on the A-site. Surprisingly, the optical properties of these highly crystalline thin films are even superior to the one of FASnI3 single crystals.
[1] S. Shao, J. Liu, G. Portale, H.-H. Fang, G. R. Blake, G. H. ten Brink, L. J. A. Koster, M. A. Loi. Adv. Energy Mater. 8, 1702019, 2018; E. Jokar, C.-H. Chien, C.-M. Tsai, A. Fathi, and E. W.-G. Diau. Adv. Mater., 31, 1804385, 2019; X. Jiang, F. Wang, Q. Weiet al. Ultra-high open-circuit voltage of tin perovskite solar cells via an electron transporting layer design. Nat Commun 11, 1245 (2020).
[2] H.-H. Fang, S. Adjokatse, S. Shao, J. Even, M. A. Loi. Nat. Commun. 9, 243, 2018.
[3] S. Kahmann, S. Shao, M. A. Loi Adv. Funct. Mater., 29, 1902963 (2019).
S-I3
The major problem with Sn halide perovskites for use in photovoltaic cells is the high self-doping that occurs upon oxidation resulting in a highly-doped semiconductor that is not ideal for photovoltaic use. While some control over this doping has been achieved, it is still an important problem, resulting in much lower conversion efficiencies compared with Pb-based perovskite cells.
In this talk, I will describe various mechanisms leading to the high doping levels. I will discuss some already-used methods of reducing self-doping and suggest future ways of mitigating this doping and perhaps learning more about the effect of doping of these materials in general.
S-I4
The development of high performance lead free perovskite solar cells (PSCs) is important to address the environmental concern of heavy metal lead. In recent years, tin perovskite solar cell (TPSCs) is developing quickly and emerging as a promising candidate for high efficiency lead free PSCs. In this presentation, I will summarize recent work of our group about tin perovskite solar cells, including the use of low-dimensional structure and film structure manipulation, crystal growth kinetic control to manipulate its nanostructure, as well as device structural engineering to reduce interface carriers recombination. In the end, the challenges for TPSCs and potential strategies toward high efficiency TPSCs will be discussed.
S-I5
Tin-iodide perovskites show comparable optoelectronic properties to lead-iodide perovskites and are good candidates for next generation lead-free perovskite solar cells.[1] Despite significant progress, however, the device efficiency of tin-halide perovskites is still limited by two apparently related phenomena, i.e. self p-doping and tin oxidation.[2]
In this work, we present a study of the MASnI3 defect chemistry, considered as a prototype of the entire materials class, based on state of the art density functional theory. We show that the inherently low ionization potential of MASnI3, compared to e.g. lead perovskites, is responsible of the high stability of acceptor defects such as tin vacancy and interstitial iodine, which are at the origin of the material p-doping.[3] The emergence of deep electron traps associated to under-coordinated tin defects (e.g. interstitial tin) and promoting non radiative recombination is also reported.[4]
The occurrence of intrinsic mechanisms leading to the oxidation of Sn(II) to Sn(IV) is investigated through the analysis of the thermodynamic stability of Sn(IV) defects within the bulk and at the surface of MASnI3. According to our predictions, tin oxidation is unfavorable in bulk MASnI3 while it is energetically favored at unpassivated perovskite surfaces. Sn(IV) at the surface acts as a deep electron trap, enhancing non-radiative carrier recombination, and can promote the lattice degradation to bulk Sn(IV) phases, i.e. SnI4 and MA2SnI6. The stoichiometry and the valence band surface pinning are found to largely influence the formation of Sn(IV). Hence, compositional engineering and surface passivation strategies are key to obtain efficient and stable tin-halide solar cells.
References
Noel et al. Energy Environ. Sci. 2014, 7, 3061-3068.
Nasti et al. Adv. Energy Mater. 2020, 10, 1902467
Milot et al. Adv. Mater. 2018, 30, 1804506.
Meggiolaro et al. J. Phys. Chem. Lett. 2020, 11, 3546-3556.
S-I6
Tin is the closest relative of lead electronically. But they are substantially different chemically. This talk reports our recent observations on the chemistry of tin perovskites, including its oxidation by conventional solvent [1], comproportionation [2], and stabilization in operating LEDs [3].
References
[1] Saidaminov, M. I.; Spanopoulos, I.; Abed, J.; Ke, W.; Wicks, J.; Kanatzidis, M. G.; Sargent, E. H. Conventional Solvent Oxidizes Sn(II) in Perovskite Inks. ACS Energy Lett. 2020, 5 (4), 1153–1155.
[2] Lin, R.; Xiao, K.; Qin, Z.; Han, Q.; Zhang, C.; Wei, M.; Saidaminov, M. I.; Gao, Y.; Xu, J.; Xiao, M.; Li, A.; Zhu, J.; Sargent, E. H.; Tan, H. Monolithic All-Perovskite Tandem Solar Cells with 24.8% Efficiency Exploiting Comproportionation to Suppress Sn(Ii) Oxidation in Precursor Ink. Nat. Energy 2019, 4 (10), 864–873.
[3] Liang, H.; Yuan, F.; Johnston, A.; Gao, C.; Choubisa, H.; Gao, Y.; Wang, Y.; Sagar, L. K.; Sun, B.; Li, P.; Bappi, G.; Chen, B.; Li, J.; Wang, Y.; Dong, Y.; Ma, D.; Gao, Y.; Liu, Y.; Yuan, M.; Saidaminov, M. I.; Hoogland, S.; Lu, Z.; Sargent, E. H. High Color Purity Lead‐Free Perovskite Light‐Emitting Diodes via Sn Stabilization. Adv. Sci. 2020, 7 (8), 1903213. https://doi.org/10.1002/advs.201903213.