I Have a Research Support System

Saturday.

Xu Qiuzhai was in the dormitory, using his computer to check the literature that his senior sister had copied to him, about organic solar cells with flexible substrates.

The number of documents is not much, less than ten, and the grades of journals are generally not high, all of which are from the second district of SCI, and there are no articles from the first district.

As for why there are no articles in the third and fourth districts, Xu Qiu learned from the senior sister that it is because Mr. Wei only searches the periodicals in the first and second districts, organizes them and sends them to the students.

After spending more than two hours, Xu Qiu roughly read all the documents and got the information he wanted:

Flexible substrates are usually made of polyester, PET or PEN.

The glass transition temperatures of PET and PEN are around 70 and 120 degrees Celsius, respectively.

Therefore, when using them as substrates to prepare battery devices, the processing temperature of transport layer and effective layer materials should not 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 Xu Qiu thought about it, he felt that it was too risky to rashly use a transmission layer material that he hadn't used before.

Because it takes a lot of time to explore the conditions, the final result may not be satisfactory, so it is better to modify the materials you are familiar with.

In the end, 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 message:

The project given to me by Mr. Wei used to use flexible substrates, so I need to order a batch of PEN substrates coated with ITO film. Is there any way for me to do so?

Within a few minutes, he received a reply from his 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 also left a problem of solution dissolution unresolved.

However, at present, only when the effective layer solution is prepared, there is a need for overnight stirring, that is, the stirring time is longer than 12 hours.

For example, when preparing a zinc oxide prepolymer solution, it only needs to be stirred for two hours, and the problem is not serious.

Xu Qiu entered the glove box, picked up the effective layer solution prepared yesterday, and gently shook the bottle, and it was obvious that there were undissolved polymer materials hanging on the wall of the bottle.

He stared at the small brown bottle, lost in thought.

Why is the solution stirred overnight?

Because the molecular weight of the polymer is relatively large, it is difficult to dissolve, and long-term stirring is required to fully dissolve it.

Is there any way to quickly dissolve the polymer?

Its concentration can be reduced.

However, 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 Polymer Condensed Matter Physics learned last semester talked about the time-temperature equivalence principle of polymers.

He can't remember the specific description, but the general meaning should be that increasing the temperature can shorten the time.

In order to test this idea, Xu Qiu quit the simulation laboratory.

He found the textbook Condensed Matter Physics of Polymers on the bookshelf, looked through the catalog, and soon found the introduction of Principle of Equivalence of Time and Temperature:

The same mechanical relaxation phenomenon of polymer can be observed at higher temperature and shorter time (or higher action frequency), and can also be observed at lower temperature and longer time. Therefore, increasing the temperature and prolonging the observation time are equivalent to the molecular motion, and are also equivalent to the viscoelastic behavior of polymers.

This is about the mechanical relaxation phenomenon of polymers, not the dissolution process, but Xu Qiu thinks it may be possible to extend it.

Because the dissolution process is also a molecular motion process of polymers, increasing the temperature and prolonging the stirring time should also be equivalent.

Moreover, in a nitrogen atmosphere, the two materials that make up the effective layer are very stable to heat, and there is no problem with resisting a temperature of 100 degrees Celsius, otherwise there would be no thermal annealing step.

However, in this case, it is not suitable to use chloroform solvent, because it has a low boiling point and cannot be heated to a 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 and stirring platform to 90 degrees Celsius, and finally put the effective layer solution on the heating platform.

To verify the idea, you need to wait for a while, so Xu Qiu decided to prepare some other concentrations of PTB7-TH:PC[70]BM effective layer solution.

The solvents are all chlorobenzene, the concentrations are 10, 20, and 25 mg/mL respectively, and the mass ratio of donor and acceptor is still fixed at 1:1.5, 1 mL each.

He wanted to see what the limiting solubility of the polymer was.

After preparing the solutions, Xu Qiu recorded the four solutions as 10#, 15#, 20#, and 25# solutions according to their respective concentrations.

After putting the 10#, 15#, and 25# solutions on the heating and stirring table, he picked up the first prepared 15# solution, 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 had passed.

Sure enough, the time-temperature equivalence principle can also be used in the dissolution of polymers.

Moreover, the effect of temperature on time is exponential. Although the current heating at 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 rack and let it slowly drop to room temperature.

Then start to spin-coat zinc oxide substrates, a total of 12 pieces.

While waiting for the substrate to be annealed, he returned to the glove box to check the dissolution of each solution.

It was found that after cooling the 15# solution on the bottle rack, the internal liquid turned into a gel.

Xu Qiu shook the bottom of the bottle vigorously, but the gel underneath did not move. In the end, he had to put 15# on the heating and stirring table to heat again.

He then checked the other three concentrations of solutions, 10# and 20# were completely dissolved, but 25# was not completely dissolved, and there were still solid particles on the bottle wall.

Xu Qiu put the 10# and 20# solutions on the bottle rack to cool down.

Then use a pipette gun to add 667 microliters of chlorobenzene solvent to the 25# solution, dilute its concentration to 15 mg per milliliter, and re-label 25#15#, and then put it on the heating platform.

Afterwards, Xu Qiu recorded the meaning of each solution number in the experiment notebook.

Entering the glove box again, he found that the 15# solution had partially released the gel state and began to turn into a solution again.

The 10# solution can maintain the dissolved state at room temperature, and the 20# solution also appears the phenomenon of gel.

That is to say, at room temperature, PTB7-TH:PC[70]BM with a mass ratio of 1:1.5 has a limit solubility of 10-15 mg/mL in chlorobenzene solvent, and at 90 degrees Celsius, the limit solubility is 20- 25 mg per ml.

Increasing the temperature can not only increase the dissolution rate, but also increase the solubility at the same time.

The problem of solution dissolution is solved.

But, a new problem appeared again.

How should these solutions be spin-coated?

Dilute them all to 10mg/ml concentration, wait for it to cool before applying?

Or don't dilute it, just apply it while it's hot?

However, considering that this week's experiment time has already been filled.

Let's not worry about this problem for now, and wait until next week to continue the experiment and save some points.