Chapter 16: Spin coating

　　 In the afternoon, the laboratory.
　　As soon as I saw Xu Qiu, Chen Wanqing said on the initiative: "School brother is here, I will teach you spin coating today."
　　 "Okay." Xu Qiu replied.
　　 He thought that he usually took the initiative to ask the senior sister for advice. Today, the senior sister is so enthusiastic, but he didn't care too much.
　　 chatted for a while, the two put on lab coats and started to work.
　　 [Spin ​​coating skills detected, whether to record? 】
　　 "Record."
　　 "The system, can you automatically record the skills related to the experiment afterwards?"
　　【Yes. 】
　　…………
　　"The main instrument used in spin coating operation is a homogenizer.
　　 First, drop the solution on the substrate, and then use the homogenizer to rotate the substrate at high speed. Under the action of centrifugal force, the solution is quickly thrown away, and the solvent in the solution evaporates, finally forming a uniform solid film.
　　 Usually, the thickness of the film prepared by spin coating is between a few nanometers and a few hundred nanometers.
　　 There are now two homogenizers in our laboratory, one in the glove box and one outside the glove box.
　　 Today, I will teach you the spin coating methods of three solutions, namely PEDOT, zinc oxide and effective layer solution.
　　 First is PEDOT, pay attention to when spin coating..."
　　 After finishing the introduction, Chen Wanqing said: "The principle and operation method are like this, do you have any questions?"
　　 "No problem, I understand everything." Xu Qiu said.
　　 "Okay...then I'll go back. This afternoon, I should only have enough time to apply PEDOT and zinc oxide. If the effective layer is applied, wait until Sunday." Chen Wanqing said.
　　 "Hmm." Xu Qiu nodded.
　　 He felt the senior sister was a little strange, what happened to her today?
　　 Forget it, I don’t want to, the experiment is important.
　　…………
　　 Through reading the literature these days, Xu Qiu has roughly understood the structure of organic solar cell devices.
　　 is usually divided into normal structure and inverted structure.
　　 The normal structure is glass as the substrate and ITO on it as the positive electrode material. Then spin coating is used to prepare the hole transport layer and effective layer, and finally the electron transport layer and negative electrode material are prepared by vacuum coating (evaporation).
In the 　　 inverted structure, first is the glass substrate, ITO is the negative electrode material, then spin coating is used to prepare the electron transport layer and the effective layer, and finally the hole transport layer and the positive electrode material are prepared by the evaporation method.
　　Cleaning substrates, preparing solutions, spin coating, and vacuum coating are the four major skills for preparing organic solar cells. After learning spin coating today, only evaporation is left.
　　 Xu Qiu turned on the auxiliary system for experimental operation.
　　 First is the preparation of PEDOT film.
PEDOT is a water-soluble polymer material with high conductivity. In order to increase its solubility, it is usually necessary to add a certain proportion of polystyrene sulfonate (PSS), so strictly speaking, it is called PEDOT: PSS is more appropriate.
　　 Xu Qiu first used a nitrogen gun to dry 24 substrates and put them in two petri dishes.
　　 Then put the petri dish with the lid removed into the ozone generator and process for 30 minutes.
　　Ozone is difficult to store, and the oxygen in the air can be converted into ozone with an ozone generator.
　　 Treating the substrate with ozone can increase the wettability of its surface, so that the liquid can easily stay on the substrate during the spin-coating process, and avoid obtaining a thin film with holes.
　　 Taking advantage of the ozone treatment, Xu Qiu took out the reagent bottle containing the PEDOT aqueous solution from the refrigerator's cold room, used a disposable dropper to about 2ml of the solution, and transferred it to a 4ml centrifuge tube.
　　 Then take out a 1ml disposable syringe, remove the needle and fill up with the solution, add a 0.22 micron water phase filter to the head of the syringe.
　　……
"What's the taste."
　　 Xu Qiu suddenly smelled a faint fishy smell.
　　 He quickly reacted, it should be ozone leaking.
　　Because of the low toxicity of ozone, he didn't wear a gas mask, he took a breath and walked to the ozone generator.
　　 First stop the instrument, and then start the inspection.
　　 The instrument door was closed tightly, and the rubber hose at the back of the instrument was connected to the outside of the window.
　　 It looks like everything is normal, so how does the smell come out?
　　 Is it there?
　　 Xu Qiu had an inference in his heart. He found the toolbox, pulled out a roll of 3M black electrical tape from it, and then returned to the ozone generator with the tape.
　　 At this time, the smell of ozone has almost dissipated.
　　 He walked around to the hose behind the instrument and carefully checked section by section.
　　 Sure enough, a rubber hose was cracked due to aging, and judging from the fracture marks, it should have just been broken.
　　 Xu Qiu glued the cracks together with tape.
　　 Turn on the instrument again, this time I can't smell the ozone.
　　 However, sticking with tape is only a stopgap measure, the best way is to replace a new rubber tube.
　　 So, Xu Qiu shouted:
　　 "Senior sister, the hose of the ozone generator is cracked. I will stick it with tape now, and then I need to get a new tube."
　　 "Okay, I wrote it down." Chen Wanqing said.
　　 After solving this little trouble, Xu Qiu continued the experiment after the countdown of the ozone generator was over.
　　 He took the petri dish out of the instrument, took a piece of substrate with tweezers, and placed the substrate on the platform of the gel homogenizer. UU Reading www.uukanshu.com
　　 There is a small hole under the platform, which is connected to a vacuum pump to ensure that the substrate will not move during high-speed rotation.
　　 He set the parameters of the glue spreader, the speed is 3000 revolutions per minute, and the rotation time is set to 60 seconds.
　　 Then use a syringe to squeeze about 0.1 ml of PEDOT solution to the center of the substrate, and then drag the liquid surface with the end of the filter to make the solution cover the entire substrate.
　　 Then press the start button, the homogenizer automatically turns on the vacuum pump and runs according to the preset parameters. After the platform completely stops rotating, the vacuum pump is automatically turned off.
　　 is another fool-like machine similar to an ultrasonic cleaner.
　　 Xu Qiu picked up the spin-coated substrate with tweezers. After careful inspection, he found that the spin coating was perfect. The blue-violet film covered the entire substrate, and the surface of the film was smooth without holes.
　　 Put the substrate back into the original petri dish and continue to pick up the next one.
　　 After repeated spin coating 12 times, 11 pieces were perfect, only one piece was slightly flawed, and only three-quarters of the area was coated.
　　 Xu Qiu threw the defective piece into the old substrate box.
　　 Next, is the thermal annealing step.
　　 For PEDOT:PSS film, the main function of annealing is to remove the residual moisture in it, so only the temperature is slightly higher than the boiling point of water.
　　 Xu Qiu puts the spin-coated substrate with a petri dish on a heating table set at 130 degrees Celsius, and then presses a stopwatch to count.
　　 generally takes more than 30 minutes.
　　 After a long wait, Xu Qiu returned to the desk, planning to take a drink and take a break.
　　 Suddenly, the senior sister next to him asked abruptly: "Xu Qiu, what are your plans for the future?"
　　 Xu Qiu almost squirted out the water he drank into his mouth.