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Rapid Synthesis of Copper Zinc Tin Sulfide (CZTS) & Lead Perovskite Nanocrystals for 
Solar Cells & Associated Environmental Nanotoxicity 
 
 
Kelly A. Collins 
 
 
 
 
 
 
 
 
 
 
 
 
 
In completion of the Undergraduate Research Opportunities Program (UROP) at the University 
of Minnesota – Twin Cities 
Under direction of Professor Eray Aydil of the Chemical Engineering & Materials Science 
Department  
Abstract: Copper zinc tin sulfide (CZTS or 
Cu2ZnSnS4) and lead perovskite (CH3 NH3 PbI3) 
nanoparticles were synthesized and then transformed 
to be dispersible in nonpolar solvents through an 
exchange reaction. These water soluble particles 
were then added to colonies of common Shewanella 
oneidensis bacterium and results of the effect of the 
particles on the bacterium are currently in process. 
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Motivation: 
To synthesize copper zinc tin sulfide (CZTS or Cu2ZnSnS4) and lead perovskite (CH3 
NH3 PbI3) nanoparticles and observe their effect on the growth of the common bacteria strain 
Shewanella oneidensis. 
Background:  
Nanoparticles are an increasingly common component of many new technologies, yet the 
environmental impact they may harbor is still widely unexplored.  
Biofilms are the most common arrangement of bacteria in the Earth’s environment, thus 
studying the impact of nanocrystals on the growth and development of a common biofilm 
bacteria strain yields a generalizable representation of the nanoparticle toxicity. Shewanella 
oneidensis bacterium will be observed because these bacteria are found globally and represent a 
critical member of the ecosystem and food chain. In this experiment CZTS and lead perovskite 
nanoparticles will be synthesized and analyzed. 
Procedure: 
 Synthesis of Lead Perovskite: 38.1 mg of lead (II) bromide and 6.4 mg of methyl 
ammonium bromide are each dissolved in 100 µL of DMF. Both solutions are gently heated and 
stirred to aid the dissolving process. 
 In a round flask 2 mL of ocadecene is combined with 95.8 µL of oleic acid and then 0.05 
mmol tetraoctylammonium bromide. This solution is stirred and heated to 80º C, then both DMF 
solutions are added to the flask and the perovskite particles are immediately precipitated with 
acetone. This solution is then centrifuged at 4,000 rpm for 20 minutes, the supernatant is 
decanted, and the nanoparticles are dispersed in toluene. 
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 Synthesis of CZTS: Three precursory solutions – Cu(dedc)2, Zn(dedc)2, and Sn(dedc)4 – 
must be synthesized in order to produce the CZTS nanocrystals.  
 From the literature synthesis stated in L.C. Schmidt’s “Nontemplate Synthesis of 
CH3NH3PbBr3 Perovskite Nanoparticles” article, Cu(dedc)2 is produced by dissolving 9.0 g of 
sodium diethyldithiocarbamate trihydrate in 150 mL of reagent alcohol. In a separate reaction 
4.23 g of copper(II) chloride is dissolved in 50 mL of reagent alcohol. The first solution is then 
slowly added to the second with constant stirring. A black precipitate will form which must be 
filtered and washed four times with deionized water to remove unwanted salts. To remove the 
water it must then be washed twice with acetone and dried in a desiccator under rough vacuum.  
 The procedure to produce Zn(dedc)2 is identical for that of Cu(dedc)2 except for the use 
of 3.38 g of zinc chloride in place of the copper(II) chloride. 
 Sn(dedc)4 is produced by dissolving 9.6 g of sodium diethyldithiocarbamate trihydrate in 
140 mL of reagent alcohol. In a separate reaction 3.0 g of tin(IV) chloride is dissolved in 50 mL 
of reagent alcohol. The first solution is added drop by drop to the second solution with constant 
stirring, as with the previous syntheses above. An orange precipitate will form. This precipitate 
must be rinsed thoroughly with deionized water and then two rinses with ice-cold acetone. This 
precipitate is then dried in a desiccator with a roughing pump for at least an hour. The crystal has 
thus formed, but it is necessary to purify it through recrystallization since possible side reactions 
like tin(II)-diethyldithiocarbamate may have formed. The orange powder is this time washed 
four times with deionized water, twice with cold acetone, and dried in a desiccator. The powder 
is then dissolved into 800 mL of boiling acetone while stirring vigorously. This solution boils 
until it becomes cloudy (at about 650 mL remaining) and the flask is then carefully removed 
from heat and allowed to cool to room temperature overnight. After this, the flask is the cooled 
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to -20 °C in a freezer for a total of one day. These newly formed crystals are then washed 
multiple times with ice-cold acetone and filtered to only keep the millimeter-sized reddish-
orange crystals which are dried in a desiccator under rough vacuum. These crystals should be 
stored in a freezer.  
 Based on stoichiometry, 54 mg of Cu(dedc)2, 27.2 mg of Zn(dedc)2, and 53.4 mg of 
Sn(dedc)4 yields about 30 mg of Cu2ZnSnS4 nanocrystals. These three powders are mixed with 4 
mL of colorless or very faint yellow oleic acid and 1 mL of 1-octadecene. A yellow oleic acid 
indicated oxidation through air exposure during storage or distillation. This new mixture is 
heated to 60 °C while being stirred rapidly, then degassed at 10 mTorr for several minutes and 
purged with dry nitrogen gas in order to remove air from the flask. The degassing and purging 
are repeated three times. The resulting mixture is then heated to 140 °C under a continuous flow 
of dry nitrogen gas. All of the solids will be completely dissolved at this temperature within one 
minute. The solution should not, however, reach 175 °C in order to eliminate the chances of 
forming binary tin sulfide precipitates (i.e. SnS2). This solution must then be cooled and kept at 
75 °C. 
 In a separate reaction 10 mL of oleylamine must be similarly degassed and purged three 
times at 60 °C. This solution must then be heated to the desired synthesis temperature between 
150-340 °C with constant stirring. This synthesis temperature will determine the average CZTS 
nanocrystal size produced. 
 The first mixture (stored at 75 °C) must then be extracted with a syringe and quickly 
injected into the flask containing the hot oleylamine. This reaction will turn black, bubble, and 
fume for several minutes. The addition of the first mixture causes the hot oleylamine temperature 
to drop by about 10-15%, but it quickly returns to its original oleylamine temperature in under 
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two minutes. After the reaction has passed this mixture must be stored under the fume hood for 
ten minutes. The flask must then be placed in a cold water bath to reduce it to room temperature. 
This is done in order to limit the handling of hot organics which can be very hazardous.  
 Lastly, the CZTS nanocrystals are precipitated by the addition of about 30 mL of reagent 
alcohol and centrifuging the solution for about 5 minutes. The supernatant is then discarded and 
the nanocrystals are dispersed in about 1 mL toluene by sonication after adding about 0.3 mL of 
neat oleic acid. The crystals are then washed with the 20 mL of the reagent alcohol and 
centrifuged for five minutes again. The final step in producing the desired CZTS nanocrystals is 
to discard the colorless supernatant and re-disperse the nanocrystals in 1 mL toluene with 0.01 
vol% oleic acid and sonicate it for an hour.  
Exchange Reaction: The exchange reaction is performed identically for both the 
perovskite and CZTS nanoparticles. First, 0.55 g of potassium sulfate or citric acid (depending 
on the trial) is dissolved in 1 mL of deionized water and 2 mL of formamide. This process is 
accelerated by sonicating and gently heating the vial. 1 mL of 2 mg/mL solution of particles 
(either perovskite or CZTS) dispersed in toluene is then added to the vial and stirred for  about 
three hours (the reaction should be stirred for more than one, but less than sixteen hours).  
Once the stirring has been stopped 1 mL of toluene is added to each vial and allowed to 
sit for five minutes to separate. The toluene layer is then removed from the top of the vial with a 
pipette and 2 mL of acetonitrile is added to precipitate the particles from the formamide 
containing potassium sulfate or citric acid. This solution is centrifuged at 4,000 rpm for 20 
minutes and the supernatant is then decanted.  
To clean the nanoparticles they are re-dispersed in 2 mL of fresh formamide and 
sonicated for about one minute. Then 2 mL each of acetonitrile, acetone, and toluene are added 
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to precipitate the particles. This solution is then 
centrifuged at 4,000 rpm for 20 minutes and the 
supernatant is decanted. This cleaning process is repeated 
three times and after the final supernatant is decanted the 
particles are re-dispersed in deionized water and sonicated 
for about one minute. 
Discussion: 
 The samples were made following the literature 
procedure and yielded concentration of 6 mg/mL. The synthesis of lead perovskite particles is a 
more recent chemical discovery, thus synthesis was carried out, but the particles are still in a 
state of being tested with x-ray diffraction and transition electron microscopy to determine 
characteristics and stability before nanotoxicity trials are conducted. For these reasons the 
exchange reaction and nanotoxicity studies have only been minimally performed with the CZTS 
particles at this time. 
 The particles were soluble in nonpolar solvents when initially synthesized, but, in order 
to test their effects on bacteria, they needed to be dispersible in water as to not harm the bacteria 
samples with a nonpolar solvent. The exchange reaction previously described was carried out for 
CZTS particles and the separation was apparent and as expected, as shown in Figure 1. The 
particles were then cleaned in the process previously described and dispersed in water for testing 
with the bacteria. 
 The water dispersed CZTS particles were then given to our collaborator Christy Haynes 
in the chemistry department of the University of Minnesota for exploration of their reaction with 
bacteria, which is currently in progress. 
Figure 1 - During (left) and after (right) the 
exchange reaction of CZTS nanoparticles. 
Note the mix of stirring layers separates into 
(from top to bottom) a thin layer of 
toluene,a thick layer of particles, and 
discardable supernatant. 
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Future Goals: 
 Once the lead perovskite particles have been characterized they will also undergo the 
exchange reaction to become dispersible in water. Both particles can then be examined at various 
concentrations with bacteria to determine what effects they may have on the environment. 
Acknowledgements: 
 I’d like to thank the Undergraduate Research Opportunities Program (UROP) at the 
University of Minnesota for providing me with this unique research opportunity and 
understanding that a research project cannot always be completed in just one semester. 
I’d also like to thank Professor Eray Aydil of the Chemical Engineering & Materials 
Science department and Professor Christy Haynes of the Chemistry department as well as all of 
their researchers for welcoming me into their groups as part of the MRSEC joint departmental 
project. A special thanks to Shreyashi Ganguly of the Aydil lab for guiding me through this 
entire process and being a wonderful mentor. Also, thank you to Bryce Williams of the Aydil 
group for providing CZTS samples, Sunipa Pramanik of the Haynes group for performing 
toxicity results and helping further my understanding of the project, and the Characterization 
Facility at the University of Minnesota for their equipment and training. 
 
References: 
Aydil, E. S., et al. "Rapid facile synthesis of Cu2ZnSnS4 nanocrystals." Journal of Materials 
Chemistry A (Royal Society of Chemistry), May 2014: 10389-10395. 
Aydil, E. S., et al. "Supplementary Information For Rapid facile synthesis of Cu2ZnSnS4 
nanocrystals." Journal of Materials Chemistry A (Royal Society of Chemistry), May 
2014: 10389-10395. 
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Maurer-Jones, Melissa A., Ian L. Gunsolus, Ben M. Meyer, Cole J. Christenson, and Christy L. 
Haynes. "Impact of TiO2 Nanoparticles on Growth, Biofilm Formation, and Flavin 
Secretion in Shewanella oneidensis." Analytical Chemistry (ACS Publications), 2013: 
5810-5818. 
Schmidt, L. C., Pertegas, A., Gonzales-Carrero, S., Malinkiewicz, O., Agouram, S., Espallargas, 
G. M., . . . Perez-Prieto, J. (2014, January 3). Nontemplate Synthesis of CH3NH3PbBr3 
Perovskite Nanoparticles. Journal of The American Chemical Society, 850-853. Retrieved 
from http://pubs.acs.org/doi/abs/10.1021/ja4109209