Chapter 38: Time-temperature equivalence principle

on Saturday.
　　 Xu Qiu stayed in the dormitory, and used the computer to check the documents copied to him by the senior sister about the flexible substrate organic solar cells.
　　 The number of documents is not much, there are less than ten articles. The grade of journals is generally not high. They are all in the second area of ​​SCI, and there is no article in the first area.
　　 As for why there are no articles in the third and fourth districts, Xu Qiu learned from the senior sister that it is because Teacher Wei only searches the journals in the first and second districts, sorts them out and sends them to students.
　　 Xu Qiu spent more than two hours reading all the documents, and got the information he wanted:
　　The flexible substrate usually uses polyester material, PET or PEN.
　　 The glass transition temperatures of PET and PEN are about 70 and 120 degrees Celsius, respectively.
　　 Therefore, when manufacturing battery devices based on them, the processing temperature of the transmission layer and the effective layer materials cannot be too high.
　　The solution in the literature is to use a low-temperature method to prepare metal oxides as transport layer materials, such as titanium dioxide and tin oxide.
　　 After thinking about it, Xu Qiu felt that it was too risky to use transmission layer materials that had not been used before.
　　Because it takes a lot of time to explore the conditions, the final result may not be satisfactory. It is better to modify the materials you are familiar with.
　　 Finally, he decided to use PEN as the substrate, first tried to use PEDOT:PSS as the transport layer material, lowered its annealing temperature to 100 degrees Celsius, and extended the annealing time.
　　 After confirming the base, Xu Qiu sent Chen Wanqing a WeChat:
　　 "The project that Mr. Wei gave me before requires a flexible substrate, so I need to order a batch of PEN substrates coated with ITO film. Is there any way out for my sister?"
　　 Within a few minutes, he received a reply from the senior sister.
　　 "Okay." A peach cat's expression.
　　 "Wait for my news."
　　…………
　　 Xu Qiu put down his phone, closed his eyes and did a set of eye exercises, then took a short break and entered the simulation laboratory.
　　 Yesterday, there was still a problem of solution dissolution that was not solved.
　　 However, at present, only when the effective layer solution is prepared, there is a need for overnight stirring, that is, the stirring time is greater than 12 hours.
　　It is like preparing a zinc oxide prepolymer solution. It only needs to be stirred for two hours, and the problem is not big.
　　 Xu Qiu entered the glove box, picked up the effective layer solution prepared yesterday, and gently shook the bottle. You can clearly see the undissolved polymer material hanging on the bottle wall.
　　 He stared at the little brown bottle, lost in thought.
　　Why should the solution be stirred overnight?
　　Because the polymer has a large molecular weight, it is difficult to dissolve it, and it takes a long time to stir to make it fully dissolved.
　　 Is there any way to make the polymer dissolve quickly?
　　 can reduce its concentration.
　　 But if the concentration is lowered, the thickness of the spin-coated film will become thinner, so it is not a good method.
　　 Is there any other way?
　　 Xu Qiu suddenly thought that the principle of time-temperature equivalence of polymers was mentioned in "Polymer Condensed Matter Physics" that I learned last semester.
　　 He can't remember the specific description, but the general idea should be that increasing the temperature can shorten the time.
　　 In order to verify this idea, Xu Qiu quit the simulation laboratory.
　　 He found the textbook "Polymer Condensed Matter Physics" on the bookshelf, looked through the catalog, and quickly found the introduction of "time-temperature equivalence principle":
The same mechanical relaxation phenomenon of 　　 polymer can be observed at higher temperature and shorter time (or higher frequency of action), or at lower temperature and longer time. Therefore, increasing the temperature and prolonging the observation time are equivalent to molecular motion, and to the viscoelastic behavior of polymers.
　　 This is about the mechanical relaxation of polymers, not the dissolution process, but Xu Qiu thinks it might be possible to extend it.
　　Because the dissolution process can be regarded as the molecular movement process of the polymer, increasing the temperature and extending the stirring time should also be equivalent.
　　 And in a nitrogen atmosphere, the two materials constituting the effective layer are very stable to heat, and there is no problem with resistance to a temperature of 100 degrees Celsius, otherwise there will be no thermal annealing step.
　　 However, in this case, the use of chloroform solvent is not appropriate, because it has a low boiling point and cannot be heated to a very high temperature.
　　 Xu Qiu returned to the simulation laboratory.
　　 First put the zinc oxide prepolymer solution prepared yesterday on the lid of the petri dish, then set the temperature of the heating stirring table to 90 degrees Celsius, and finally put the effective layer solution on the heating table.
　　If you want to verify your idea, you need to wait for a while, Xu Qiu decided to prepare some other concentrations of PTB7-TH:PC[70]BM effective layer solution.
"Chlorobenzene" is selected as the solvent, and the concentration is 10, 20, and 25 mg/ml respectively. The mass ratio of the donor to the receptor is still fixed at 1:1.5, each 1 ml.
　　 He wants to see what the limit solubility of the polymer is.
　　 After preparing the solutions, Xu Qiu recorded the four solutions as 10#, 15#, 20#, 25# solutions according to their respective concentrations.
　　 After putting the 10#, 15#, 25# solution on the heating and stirring table, he picked up the 15# solution that was first prepared, and gently shook the bottle again, and found that there was no solid residue hanging on the bottle wall.
　　 He glanced at the time, only half an hour passed.
　　 Sure enough, the "time-temperature equivalence principle" can also be used to dissolve polymers.
　　Moreover, the influence of temperature on time is exponential. Although the current heating of 90 degrees is only 30 degrees higher than the usual 60 degrees, the dissolution rate may be 10 times different.
　　 Xu Qiu put the 15# solution on the bottle holder and let it slowly drop to room temperature.
　　 Then spin-coated zinc oxide substrates, a total of 12 pieces.
　　While waiting for the substrate to anneal, he returned to the glove box to check the dissolution of each solution.
　　 It was found that the liquid inside the 15# solution on the bottle rack turned into a gel after cooling.
　　 Xu Qiu vigorously shook the bottom of the bottle ~EbookFREE.me~ but the gel underneath did not move. In the end, he had to put 15# on the heating mixing table again to heat.
　　 He then checked the other three concentrations of solutions, 10# and 20# were completely dissolved, 25# was not completely dissolved, there were still solid particles on the bottle wall.
　　 Xu Qiu put 10#, 20# solution on the bottle rack to cool.
　　 Then use a pipette to add 667 microliters of chlorobenzene solvent to the 25# solution, dilute its concentration to 15 mg/ml, and re-label the 25#15#, and then put it on the heating table.
　　 Subsequently, Xu Qiu recorded the meaning of each solution number in the experiment notebook.
　　 entered the glove box again, he found that 15# solution had partially lifted its gel state and began to change into solution again.
　　 10# solution can maintain a dissolved state at room temperature, while 20# solution also appears gel.
That is to say, at room temperature, PTB7-TH:PC[70]BM with a mass ratio of 1:1.5 in chlorobenzene solvent has a limit solubility of 10-15 mg/ml, and at 90 degrees Celsius, the limit solubility is 20- 25 mg per milliliter.
　　The increase in temperature can not only increase the dissolution rate, but also increase the solubility at the same time.
　　The problem of solution dissolution is solved.
　　 It's just that a new problem has appeared again.
　　How should these solutions be spin-coated?
　　 is to dilute them to a concentration of 10 mg/ml and wait for it to cool before applying?
　　 Still do not dilute, just apply while it is hot?
　　 However, considering that the duration of the experiment this week is full.
　　 Still don't worry about this problem, wait until next week to continue the experiment, save some points.