Solvents for Processing Stable Tin Halide Perovskites

Abstract

Tin is one of the most promising alternatives to lead to make lead-free halide perovskites for optoelectronics. However, the stability of tin-based perovskites is hindered by the oxidation of Sn­(II) to Sn­(IV). Recent works established that dimethyl sulfoxide, which is one of the best-performing solvents for processing perovskite, is the primary source of tin oxidation. The quest for a stable solvent could be a game-changer in the stability of tin-based perovskites. Starting from a database of over 2000 solvents, we identified a series of 12 new solvents suitable for the processing of formamidinium tin iodide perovskite (FASnI3) by investigating (1) the solubility of the precursor chemicals FAI and SnI2, (2) the thermal stability of the precursor solution, and (3) the possibility of forming perovskite. Finally, we demonstrate a new solvent system to produce solar cells outperforming those based on DMSO. Our work provides guidelines for further identification of new solvents or solvent mixtures for preparing stable tin-based perovskites.

Fluoride Chemistry in Tin Halide Perovskites

“…This affinity of fluorides towards Sn IV can have several important implications that may reduce Sn IV content in the final film. For instance, the strong preference for Sn IV means that fluorides could complex it as soon as it is generated, whether from O 2 in the environment or DMSO‐driven oxidation [7, 8, 11] . In fact, one should think if SnF 2 would be as valuable for other solvents as in DMSO, as fluorides could be critical in sequestrating Sn IV as soon as it is oxidized by this solvent, making it less harmful.…”

Fluoridchemie in Zinn‐Halogenid‐Perowskiten

“…Zum Beispiel bedeutet die starke Präferenz fürS n IV ,d ass Fluoride es komplexieren kçnnten, sobald es erzeugt wird, sei es durch O 2 in der Umgebung oder durch DMSO-getriebene Oxidation. [7,8,11] Tatsächlich sollte man bedenken, dass SnF 2 füra ndere Lçsungsmittel genauso wertvoll sein kann wie in DMSO, da Fluoride bei der Sequestrierung von Sn IV entscheidend sein kçnnten, sobald es durch dieses Lçsungsmittel oxidiert wird, was es weniger schädlich macht. Die Umsetzung von SnI 4 zu SnF 4 wird auch die kürzlich von Lanzetta et al beschriebenen SnI 4 -getriebenen Zersetzungswege unterbinden.…”

“…Ausdiesem Grund wurden mehrere Versuche unternommen, um die Oxidation von Sn II zu verhindern. Dazu gehçrt die Verwendung neuer Lçsungsmittelsysteme zur Vermeidung der Oxidation durch Dimethylsulfoxid (DMSO), [11] der Einsatz von Reduktionsmitteln zur Verringerung des Sn IV -Gehaltes,w ie metallisches Sn-Pulver [12] oder hypophosphorige Säure [13] oder die Einführung von Additiven zur Minderung der Bildung von Sn IV ,wie das allgegenwärtige SnF 2 . [6,14] SnF 2 hat einen bemerkenswerten Erfolg als Additiv im Bereich der Zinn-Halogenid-Perowskite erzielt.…”

The green solvent: a critical perspective

“…However, DMSO -containing solvents used to process tin-based PSCs lead to loss of performance associated with oxidation of tin(II) to tin(IV). Di Girolamo et al ( 2021 ) have recently developed DMSO -free solvent systems for processing formamidinium tin triiodide perovskite based on 16 non- DMSO compounds (and 66 mixtures) selected from an initial set of 80 candidates. Characterisation and performance tests identified 6:1 N,N - diethylformamide/ N.N′ - dimethylpropyleneurea as a promising combination.…”

“…Most of these have been assembled from various compilations and data sets used in the computerised identification and selection of solvents with particular characteristics and are discussed in “ Solvent selection and design: empirical database and computational methods ” section. Some materials cited as green in additional papers [and from one website ( http://www.xftechnologies.com/solvents )] are also included (Bankar et al 2013 ; Barbaro et al 2020 ; Bauer and Kruse 2019 ; Bergez-Lacoste et al 2014 ; Byrne et al 2017 ; Byrne et al 2018 ; Calvo‑Flores et al 2018 ; Christy et al 2018 ; Clark et al 2017a ; Cseri and Szekely 2019 ; Di Girolamo et al 2021 ; Diorazio et al 2016 ; Driver and Hunter 2020 ; Estévez 2009 ; Gevorgyan et al 2020 ; Ho et al 2020 ; Hu et al 2014 ; Jessop et al 2012 ; Jin et al 2017 ; Kobayashi et al 2019 ; Lee et al 2017 ; Linke et al 2020 ; Marcel et al 2019 ; Moity et al 2014a , b ; Mudraboyina et al 2016 ; Murray et al 2016 ; Pellis et al 2019 ; Piccione et al 2019 ; Qian et al 2021 ; Samorì et al 2014 ; Shahbazi et al 2020 ; Shakeel et al 2014 ; Sherwood et al 2016 ; Strohmann et al 2019 ; Tobiszewski et al 2015 ; Vinci et al 2007 ; Wypych and Wypych 2014 , 2019 ; Yang and Sen 2010 ; Yara-Varón et al 2016; Zhenova et al 2019 ).…”