Impact of Metal Impurities on Recombination in Lead-Tin Perovskites
Florine Rombach a, Luca Gregori b, Anika Sidler c, Jayne Whitworth d, Stefan Zeiske e, Heon Jin a, Esther Hung a, Silvia Motti f, Pietro Caprioglio a, Daniele Meggiolaro g, Henry Snaith a
a Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
b Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy
c Institute for Ecopreneurship, School of Life Sciences, University of Applied Sciences and Arts Northwestern Switzerland, Hofackerstrasse 30, 4132 Muttenz, Switzerland
d Materials Innovation Factory, University of Liverpool, 51 Oxford Street, Liverpool L7 3NY, UK
e Sustainable Advanced Materials (Sêr-SAM), Department of Physics, Swansea University, Singleton Park, Swansea, Wales SA2 8PP, UK
f School of Physics and Astronomy, Faculty of Engineering and Physical Sciences, University of Southampton, University Road, Southampton SO17 1BJ, UK
g Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto CNR di Scienze e Tecnologie Chimiche (SCITEC-CNR), Via Elce di Sotto 8, 06123, Perugia, Italy.
Poster, Florine Rombach, 213
Publication date: 6th February 2024

A major strategy for tuning the optoelectronic properties of semiconductors has long been doping with small densities of foreign elements. Perovskites are a class of novel materials with promising applications including photovoltaics, light emitting diodes, and photodetectors, in which the effects of doping are only beginning to be explored. The incorporation of small densities of foreign ions can strongly affect the defect chemistry and in turn the properties of perovskite materials.

We investigate the effect of doping narrow bandgap lead-tin perovskites with small amounts of trivalent metal ions Bi3+ and Sb3+. We discover that both cause greatly increased rates of non-radiative recombination, at doping densities as low as 1 ppm for Bi3+ and 100 ppm for Sb3+. DFT calculations confirm that these metal ions can incorporate in the perovskite crystal structure, and show that they function as deep electron traps in the perovskite.

Having found that very small amounts of Bi3+ have a disastrous effect on the electronic quality of lead-tin perovskite films, we investigate the presence of Bi impurities in various perovskite precursor chemicals by inductively coupled plasma mass spectrometry, discovering significant quantities in some. In response, we introduce a facile method for removing Bi3+ impurities, with which we demonstrate the successful removal of 100 ppm Bi3+ from a perovskite precursor solution.

This work demonstrates how the incorporation of very small concentrations of foreign ions can severely affect the optoelectronic quality of perovskites, highlighting the importance of precursor chemical purity. It also demonstrates the significance of screening for trapping activity when examining potential dopants for perovskites in the future.

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