A protocol for synthesizing inorganic-lead-halide hybrid perovskite quantum dot inks for inkjet printing and the protocol for preparing and printing the quantum dot inks in an inkjet printer with post characterization techniques are presented.
The main advantages of this technique are that it is well suited for large area deposition, rapid prototyping and print by design, which suggests high potential for roll-to-roll manufacturing. Though this system can provide insight into inorganic photovoltaics it can also be applied to other systems such as organic photovoltaics or biophysics. Demonstrating the chemical synthesis procedure will be Mason McCormick, an undergraduate from the Sinitsky laboratory.
An imprinting procedure will be demonstrated by Dylan Richmond from the Ilie laboratory. To prepare the cesium oleate precursor add 0.203 grams of cesium carbonate 10 milliliters of octadecene and 1.025 milliliters of oleic acid to a three neck round bottom flask containing 2.54 centimeter magnetic stir bar. Place a thermometer into one of the necks of the round bottom flask via a rubber septum.
Next, place a rubber septum into one of the remaining necks of the round bottom flask and attach the third neck to the nitrogen gas line via a Schlenk line. Place the mixture under nitrogen atmosphere. Heat the mixture to 150 degrees celsius with constant stirring at a stirring speed of 399 millimeters per second until the cesium carbonate fully dissolves.
Following this lower the temperature to 100 degrees celsius to avoid precipitation and decomposition of the cesium oleate and continue stirring at a stirring speed of 399 millimeters per second. To prepare the oleylamine lead bromide precursor add 1.35 millimoles of lead bromide 37.5 milliliters of octadecene 7.5 milliliters of olaylamine and 3.75 milliliters of oleic acid to a three neck round bottom flask containing a magnetic stir bar. Next place a thermometer into one of the necks of the round bottom flask and seal with polymer film.
Place a rubber septum in one of the remaining necks of the round bottom flask and attach the third neck to the nitrogen gas line via a Schlenk line. Place mixture under nitrogen atmosphere. Heat the mixture to 100 degrees celsius with constant stirring at a stirring speed of 599 millimeters per second until the lead bromide is fully dissolved.
Now, heat the mixture to 170 degrees celsius with constant stirring and observe the color change to dark yellow once the temperature reaches 170 degrees celsius. Continue stirring at 170 degrees celsius. Using a two milliliter glass syringe with a 10 centimeter long 18 gauge needle extract 1.375 milliliters of cesium oleate precursor from the three neck round bottom flask.
Quickly inject this precursor into the three neck round bottom flask containing the oleylamine lead bromide precursor. After waiting five seconds remove the three neck round bottom flask from the heat and immerse it in an ice water bath. Separate the solution in the three neck round bottom flask equally into two test tubes.
Add 25 milliliters of acetone to each of the supernatant solutions. Next, separate the quantum dots using a centrifuge at 2431.65G for five minutes at room temperature. Now dissolve the separated quantum dots in 10 to 25 milliliters of cyclohexane.
To ensure that the inks print in the desired location draw a straight line at the edge of the disk and continue onto the CD disk tray. Place the desired substrate over the ink images printed on the disk and attach it to the disk using an adhesive such as double sided tape. Before filling the ink cartridges ensure the orange cover is installed correctly on the bottom of the ink cartridge to prevent ink from spilling out.
Using a pipette inject the prepared quantum dot ink into the top of the ink cartridge. Once the cartridge is filled to the desired amount of ink plug the top with the rubber septum and carefully remove the orange cover. Next place the ink cartridge in the printer head and ensure that is snaps into place.
Then insert the remaining cartridges before continuing to the next step. At this point the printer will accept the disk tray and print perovskites on the substrate. After printing is complete check that the inks actually printed onto the substrate as clogging is a common problem.
Finally hold a UV lamp over the substrate to check if the printing was successful and a luminescing film is observed. Characterization of the synthesized inorganic perovskites is vital to confirm the crystal structure. The X Ray defraction results indicate that the crystalline cesium lead bromide quantum dot inks prepared using this protocol maintain an orthorhombic room temperature perovskite structure after the ink jet printing process.
It is well known that the optical properties of these inorganic perovskite quantum dots are sensitive to quantum dot size and stoichiometry of the inorganic and halide atoms. The photoluminescence profile for cesium lead bromide shows a peak around 520 nanometers and the optical absorption profile shows an excitonic peak around 440 nanometers. Current voltage and capacitance voltage measurements were taken for the printed films under dark and light conditions as shown here.
Under illumination the measured kind increased linearly and indicates that the films are photoactive. The films exhibit very low capacitance under dark conditions when no illumination is present. As can be seen here.
Under light illumination the zero bias measured capacitance increases and is another indication that the films are photoactive. While attempting this procedure it's important to remember to keep both the printer head and gaskets as clean as possible. This will ultimately dictate successful printing.
Following this procedure other methods like probe microscopy and time resolved luminescence can be performed in order to answer additional questions like what is the surface termination and surface morphology, and what are the exciton recombination dynamics. After it's development this technique paved the way for researchers in the fields of chemistry, physics and material science to explore roll-to-roll ready, photovoltaic systems composed of organic and inorganic semi conductor materials and the associated device interfaces. This technique proved to be a great educational tool as it was introduced in the upper level inorganic chemistry laboratory course at the University of Nebraska-Lincoln to introduce students to a variety of important concepts ranging from calyceal synthesis and quantum size affects to photovoltaics and renewable energy.
Don't forget that working with lead based products and solvents like hexane, cyclohexane or acetone can be extremely hazardous and precautions such as using proper protective clothing and proper ventilation should always be taken when performing this procedure.
