Chapter 142: Deja vu

"What should I do?"
　　 In response to the gaze of the school girl asking for help, Xu Qiu thought for a moment and said:
　　 "Let me see you make a complete batch of devices, find out what is wrong, and give you some suggestions."
　　 "Okay, great." Han Jiaying said happily.
　　……
　　 After Feifei Wu finished the experiment, the school girl took over the spin coating glove box.
　　 The first step is the solution preparation.
　　 She had three materials, so she prepared three sets of chlorobenzene solvent solutions.
　　 From the perspective of solvent selection, there is no problem.
　　 After all, she doesn't have a simulation laboratory. It is a good choice to use the previous experimental conditions in the preliminary experiment.
　　 However, she changed the concentration of the solution. The concentration of P2T and P3T is 8 mg/ml, while the concentration of P5T is 6 mg/ml.
　　Xuqiu P4T system, the best concentration is 8mg/ml.
　　 In response, Han Jiaying actively explained:
　　"In the beginning, I used the condition of 8 mg/ml for all three solutions.
　　 But I found that the P5T solution at this concentration, even if the temperature of the solution is heated to 90 degrees Celsius, still cannot dissolve well, and some solid matter will remain on the bottle wall.
　　 I added some more solvent and diluted it to 6 mg/ml before it can be used normally.
　　 P2T and P3T two systems, it can be dissolved normally. "
　　 "It's the solubility problem again." Xu Qiu said with emotion.
　　 "Again?" Han Jiaying asked in confusion.
　　 "Well, when I did an experiment before, I encountered solubility problems twice," Xu Qiu explained:
　　 "However, I solved it all later. At that time you hadn't come to Teacher Wei's research group."
　　 "So, how did the brother solve it?"
　　 "The first time was to use chloroform Soxhlet extraction to process the crude polymer product to remove insoluble matter in the product," Xu Qiu said:
"The second time is the modification of the molecular structure. By increasing the length of the side chain of the changed polymer material, its solubility is fundamentally improved.
　　 Actually, I have almost guessed the cause of the solubility problem you encountered this time. "
　　 "Really or fake, so powerful?" Han Jiaying said.
　　 "After all, the three systems you made are similar to my P4T system, and the relevant experimental experience can also be used and analogized." Xu Qiu said:
"The best OD side chain used in P4T molecules is not necessarily used in P2T, P3T, and P5T molecules, but is also optimal."
　　 I guess, because the P5T molecule increases the conjugation length of the main chain, the relative proportion of the side chain will decrease.
　　 is manifested in solubility, that is, solubility is reduced. To increase its solubility, it is necessary to extend the length of its side chain.
　　 For the two molecules of P2T and P3T, shorter side chains can also meet the dissolution needs. Perhaps shortening the length of their side chains can improve performance. "
　　 "It sounds reasonable," Han Jiaying said:
　　 "Then brother, come and guess again, what are the efficiencies of these three systems?"
　　 "You... a bit too embarrassing," Xu Qiu cried and laughed:
　　 "If I know the efficiency just by looking at the molecular structure, I don't need to experiment."
　　 Seeing Han Jiaying's serious face, Xu Qiu still cooperated:
　　 "Let me guess, the P3T is the highest, I can't judge the other two."
　　 "Hey, you really guessed it," Han Jiaying said:
　　 "P3T is indeed the highest, with 4%, and P5T is the second with 3%. The efficiency of P2T is very low, less than 1%."
　　 "This way, with the result, the reason can be roughly deduced." Xu Qiu thought for a while and said:
　　"Everything assumes that there are no major problems with your experimental operation.
　　 The poor performance of P2T may be that the D unit is too small, and long side chains are attached to it, which hinders its contact with PCBM, thereby reducing the donor/acceptor interface, resulting in poor exciton splitting efficiency.
　　If the subsequent experiments still get similar results, you can temporarily abandon the research in this direction.
　　 As for P3T and P5T, as I analyzed before, the length of their side chains can be reduced and increased by one unit, and the performance may be improved. "
　　 "Unexpectedly, just a single efficiency experiment conclusion, the senior can analyze so many things." Han Jiaying said:
　　 "Hey, I got the results of the experiment before, and I was at a loss. I didn't know what to do next. Now everything is clear."
　　 "These are all conjectures from the molecular structure level. I am just pointing out the direction for improvement in the future, and it is not necessarily correct." Xu Qiu said:
　　 "You have to rely on yourself for the specifics. Of course, if you have any questions, you can still find me at any time."
　　 "Hmm," Han Jiaying nodded and said, "Then I will continue the experiment."
　　Prepare zinc oxide solution, clean the substrate, and spin-coat zinc oxide.
　　Han Jiaying has a good grasp of these basic experimental operations, and there are no obvious problems.
　　 The experiment started this afternoon, and there was not enough time to prepare and test a batch of devices.
　　 Therefore, the two agreed to continue the spin coating, evaporation and testing of the effective layer on Friday afternoon.
　　……
　　 Time flies by.
　　 At 1:20 pm on Friday, Xu Qiu and Han Jiaying entered the laboratory on time and occupied the spin-coating glove box.
　　 can still hear Wu Feifei's voice behind her:
　　 "I don't make components today, no one is robbing you of the glove box, so you are anxious."
　　 Xu Qiu ignored her, turned to the school girl and said:
　　 "It feels like Feifei Wu is envious of me, the new student Cheng Mingbo, I can hardly see others.
　　 You are still reliable, but fortunately I chose you. "
　　 Han Jiaying didn't know how to answer the call~EbookFREE.me~ After thinking for a while, she whispered:
　　 "I'm very lucky too."
　　 "What are you whispering?"
　　 "No, nothing, I'm about to start spin coating."
　　 After finishing talking, she started to heat the solution and substrate, but the experiment operation was a little flustered.
　　 Fortunately, it didn't last long, and her movements gradually stabilized.
　　 The first piece, start spin coating.
　　 Xu Qiu was watching from the side, her technique was still a bit rusty.
　　 He didn't point it out immediately, but continued to observe.
After 　　 spin coating is completed, Han Jiaying uses tweezers to pick up the substrate.
　　 Two people observe together. There is a circular pattern in the center of the film. This is caused by the real hot spin coating method. This is no problem.
　　 However, the resulting film is not very smooth, and there are a few small bumps on it, which may be undissolved polymer, or the polymer may be precipitated during the film forming process.
　　 Xu Qiu suddenly thought that he seemed to have never taught the school girl this operation seriously, because the operation was very difficult. Before, the school girl was watching by himself.
　　 However, this method can only rely on constant trial and proficiency, and there is no shortcut.
　　 "The technique of true hot spin coating is not proficient enough. This should be the reason for the low efficiency of your device," Xu Qiu commented:
　　 "Let’s practice with the glass sheet first, until you can stably obtain a uniform film."
　　 "Okay." Han Jiaying said.
After 　　, she began to practice real and hot spin coating with glass slides, and Xu Qiu guided outside.
　　 This scene is a bit familiar, as if it was the same when Chen Wanqing was taught the spraying method.
　　The difference is that Han Jiaying's talent is higher.