Chapter 40: Exam month (on)

　　 In the first week of the exam month, Xu Qiu’s daily schedule is proceeding in an orderly manner according to the plan.
　　 Simulation laboratory.
　　 Continue the experiment from last week.
　　 The problem encountered before is whether the effective layer solution should be applied hot or cold.
　　 Xu Qiu thought about it for dozens of seconds, then he patted his forehead and made a decision:
　　 Since I don’t know which condition is good, I’ll just try it all.
　　 The results of the experiment will give the answer.
　　 He had studied "Polymer Chemistry" before and knew that there are many differences between polymers and small molecules.
　　For high molecular polymer materials, it is not pure, but a mixture of polymers of different molecular weights.
　　 Therefore, it is difficult for researchers to accurately measure its components, and can only calculate its average molecular weight through experimental means.
　　 usually use number average molecular weight, weight average molecular weight, polydispersity coefficient to characterize the molecular weight of polymer materials and their molecular weight distribution.
　　 Therefore, for polymer materials prepared in different batches, their molecular weights and polydispersity coefficients are different, so the properties will naturally be different. Even the same batch of materials will be slightly different from each other.
　　 So when it comes to high polymer materials, the experimental conditions found are generally only valid for the same batch. If you change a batch, the best experimental conditions will change.
　　 Fortunately, the senior sister bought 500 mg of PTB7-TH at one time, enough for a few months, so it is necessary to spend some time to find the best conditions.
　　 Combined with the experimental conditions of other researchers in the literature, Xu Qiu designed his own experimental program.
He first took the 25#15# solution diluted last time, added 833ml of chlorobenzene solvent with a pipette again, diluted it to 10mg/ml, relabeled it as 25#10#, and then placed it in the heating at 90 degrees Celsius On the mixing table.
　　 Then remove the 10# solution from the heating and stirring table, put it on the bottle rack and wait for it to cool naturally.
　　 The other 15# and 20# solutions will not be operated and will still be placed on the heating and stirring table.
　　 A total of four sets of solutions were obtained, of which 10# was used for cold coating, 15#, 20#, 25#10# were used for hot coating.
　　 12 substrates, each group of solutions uses 3 speeds, tentatively set as 1500, 2000, 2500r.p.m..
　　 In order to reduce the experimental variables, he decided not to add solvent additives and not to perform annealing operations.
　　 Then spin coating, evaporation, and testing.
　　 Finally, the highest efficiency of this batch of devices was produced in the "20#, 2500" sample, which was 8.22%.
　　 The efficiency values ​​of all other samples are also above 7%.
　　 After completing the experiment, Xu Qiu recorded the experiment results in the experiment notebook, and then analyzed:
　　 First of all, under the current experimental conditions, the higher the solution concentration, the better the photoelectric performance.
　　Secondly, under the current experimental conditions, the cold coating method and the hot coating method have little effect on the performance of the device.
　　 Finally, a total of 12 experimental conditions were used, but the fluctuations in the photoelectric properties of the device were small. This shows that PTB7-TH has excellent performance and low dependence on experimental conditions. This point is compared with P3HT. He heard from her senior sister that when she first did P3HT, she completely referred to the experimental conditions in the literature, but the device efficiency was only less than 1%.
　　 Xu Qiu is quite satisfied with the 8.22% best efficiency data, after all, this is the first attempt.
　　 Although the results reported by other researchers' articles are generally above 10%, and even the highest is 12.2%, it is their best performance after continuous exploration and repeated improvement of experimental conditions.
After 　　, Xu Qiu changed the speed based on the results of the last time and made another batch of devices.
　　 He prepared samples of 20# solution at 2500, 3000, 3500 r.p.m. rotation speeds.
　　 The highest efficiency is produced in the "20#, 3000" sample, which is 8.40%.
　　…………
　　 On Sunday, Xu Qiu received news from her senior sister that the PEN substrate had been delivered to the laboratory.
　　 Xu Qiu ran to the laboratory.
　　 "Hey, Xu Qiu, why are you here?" Chen Wanqing said.
　　 "Senior sister said that the PEN substrate has arrived, so I'll come and have a look." Xu Qiu said.
　　 "I just want to inform you that you are not doing the experiment now, so you don't want to review it." Chen Wanqing said so, but she got up and went into the laboratory to take out the PEN substrate.
　　 Xu Qiu took the substrate and examined it carefully.
The substrate is a large roll that is rolled up, and the texture is hard when bent. Its surface is transparent with a little light yellow. One side is plated with ITO, and the side with ITO is covered with a layer of peelable Plastic protective film.
　　 Xu Qiu calls the system:
　　 "Can the system only copy the PEN substrate without changing other items in the simulation laboratory?"
　　【Yes. 】
　　 "Then copy it."
　　【The copy is successful. 】
　　 Xu Qiu suddenly thought, wouldn't it be possible to bring other things to the simulation laboratory?
　　 But thinking about it, it doesn’t seem to be of much use. Even if it can be brought in, it can’t be taken out. It’s just a virtual one.
　　 He put the PEN substrate back in his hand and asked:
　　 "Senior sister, has the experiment been going well recently?"
　　 "I am planning to make PTB7-TH devices recently, but this thing doesn't seem to dissolve well." Chen Wanqing frowned.
　　 "Well, what are the experimental conditions?"
　　" Hmm... The total concentration of the chloroform solvent I used is 10 mg/ml, giving the receptor a 1:1 mass ratio, that is, 5 mg of PTB7-TH is added.
　　 But after stirring for several days, the dissolution is still not good, and there will always be solid residue on the bottle wall.
　　 But I dare not adjust the concentration of the polymer too low, I am afraid that the film-forming properties of the solution are not good.
　　 There was no such problem when doing P3HT before, hey. "Chen Wanqing said.
　　 Xu Qiu thought to himself: "Senior Sister’s progress is a bit slow. If it continues like this, after a month, even if I find out the optimal conditions, I dare not use it directly.
　　 It's better to give the senior sister some tips, guide her step by step, let her try out a similar condition first, and finally I take out the best condition, it will not appear so abrupt. "
　　 Thinking of this, he said:
"Maybe you can try heating the solution. I recently reviewed "Polymer Chemistry" and saw that there is a time-temperature equivalence principle in it. I think it can be extended to the problem of solution dissolution. I think increasing the temperature should speed up the polymer. Dissolve."
　　 "But this is a chloroform solvent, oh -" Chen Wanqing said: "You mean changing the solvent, using chlorobenzene and dichlorobenzene? Would it cost too much raw materials?"
"I can't bear to have children but not wolves," Xu Qiu said: "And if you use the spray method, you can use 20 microliters at a time. One milliliter of solution can be used for more than 40 times. On average, the solution cost to make a substrate is just over three yuan."
　　 "Your math is really good," Chen Wanqing said: "It sounds reasonable, okay, then I'll try it."
　　 Xu Qiu didn't worry about the senior sister's experimental operation ability, and added:
　　 "The heating temperature can be slightly higher, such as 75 degrees, 90 degrees, etc., polymer and PCBM are relatively stable in a nitrogen atmosphere."
　　 "Okay, okay." Chen Wanqing nodded and recorded it.
　　 This time, there should be no problem.