I Have a Research Support System

"Xu Qiu, what do you understand?"

"I thought of an idea to further improve the performance of the device."

Xu Qiu settled down and said slowly:

"Currently, in my system, the performance of the device in the chloroform solvent is the highest, above 9%, while the performance of the device cold-coated with the chlorobenzene solvent is very low.

Only under the condition of hot coating with chlorobenzene solvent, the device efficiency can be barely equivalent to chloroform solvent, reaching 9%. I have never tried to understand the reason before.

And the sister just mentioned that the temperature of the solution during spin coating is different, which will be reflected in the light absorption spectrum of the film obtained by spin coating.

This shows that my material is different from traditional low-crystalline polymer materials, and the processing temperature during spin coating will significantly affect the microscopic morphology of its film.

The solvent used when the senior sister tested the light absorption is chlorobenzene, right? "

"That's right, all I use are chlorobenzene solvents, and chloroform solvents can't be heated." Chen Wanqing said:

"Does that have anything to do with what you said?"

"Of course it's related, don't worry," Xu Qiu said:

"In the organic photovoltaic system, the ideal microscopic morphology of the effective layer film should have a three-phase structure, including a pure polymer phase, a pure PCBM phase, and a blend of the two phases.

If the intrinsic crystallinity of the polymer material is too strong and is not suppressed, a very large crystal region will be formed in the obtained effective layer film, thereby squeezing the proportion of the blended phase, which is not conducive to the improvement of device performance. "

"I seem to understand," Chen Wanqing seemed to understand:

“You are saying that your system can focus on optimizing the blend morphology of the effective layer because of the high crystallinity of the polymer.

So, how does it work? "

Xu Qiu put on an air of "children can be taught".

After receiving a blank stare from his senior sister, he explained seriously:

"The crystallization of the polymer is not instantaneous, but takes a certain amount of time.

In spin coating, that is, during the film formation process of the effective layer, the slower the solvent volatilizes, the more time is left for the polymer to crystallize, and the larger the crystal phase size of the polymer in the resulting blended film will be.

Let's analyze the two solvents we used earlier.

Chloroform is a solvent with a low boiling point. Even if it is spin-coated at room temperature, the solvent volatilizes very quickly, and its film-forming process is also very fast.

Under such conditions, the degree of crystallinity of the polymer phase can be controlled within a reasonable scale.

But because chloroform has a very low boiling point, it cannot be heated, so it is difficult for us to fine-tune the specific scale.

However, chlorobenzene solvent is directly cold-coated, the solvent volatilizes very slowly, and the film-forming process is also very slow, which leads to a lot of crystalline phases of the polymer, which is also the reason for the poor performance of the corresponding devices.

In the hot coating method, because the temperature is increased, the solvent volatilization rate is increased, the film forming rate is faster, the polymer crystal phase is reduced, and the performance is improved.

Although the performance of devices based on chlorobenzene solvents is not as high as that of chloroform at present, fine control can be achieved by controlling the temperature during the spin coating process. "

"However, I remember that when you tested, you used a 90-degree chlorobenzene solution to heat it up." Chen Wanqing said:

"And the boiling point of chlorobenzene is only 130 degrees Celsius, so there is not much room for upward adjustment."

"Isn't there still room for 40 degrees Celsius?" Xu Qiu said:

"Besides, the main purpose of our previous hot coating method was to accelerate the dissolution of the solution, rather than considering the crystallinity, so the substrate was still a cold substrate.

This method is just a pseudo hot coating method.

We can improve this by heating the solution, along with the substrate, to the appropriate temperature.

In fact, it is best to use a spin coater with a heating platform that can control the temperature of the substrate, but we do not have that condition. "

"After your job is published, mention it to Mr. Wei, he will most likely agree to buy it." Chen Wanqing said:

"By the way, have you ever thought about which journal to submit to? If the efficiency can reach 10%, at least one article can be published in AM, even if it is only 9%, there is no problem in publishing its major sub-journal AEM.

If this is my job, I can send an AM, and the doctor will be complete. "

"Let's talk about it, let's see Teacher Wei's opinion. I didn't think too much about it. The first thing is to finish the job well." Xu Qiu said.

Han Jiaying listened in a blur.

However, as a student of the Department of Materials, AM still knows that the full name of the journal is "Advanced Materials", which is the top journal in the field of materials.

This brother, there is something, as expected, he didn't miss it before.

...

It was time for dinner, and Wu Feifei, Duan Yun, and Tian Qing also came out of the laboratory one after another.

Today, except for the new student Cheng Mingbo who did not come, everyone in the laboratory is here.

A group of people walked together in twos and threes, marching towards the cafeteria mightily.

Small research group, no thorns, get along very well with each other, there is no intrigue, and there is no obvious relationship between superiors and subordinates.

It's just that because of the experiment, Xu Qiu and Chen Wanqing have more contact.

But when we are free, we all do activities and eat together, which makes us feel like a small family.

Wu Feifei looked at Han Jiaying, who followed Xu Qiu and followed suit, and felt a little envious in her heart.

Looking at other people's juniors, and then looking at my own juniors, they only appeared once a week, and met once.

After dinner, Tian Qing, Chen Wanqing and the graduate students went back to their dormitory to rest, only Xu Qiu and Han Jiaying returned to the laboratory.

This is also normal, because the postgraduate dormitory is between the cafeteria they often go to and the first floor of the materials, so if they don't plan to work overtime, they will choose to go back and rest for a while.

But if Xu Qiu wants to go back to the dormitory, he has to go around a lot, so he usually returns to the laboratory directly after dinner.

Fortunately, there is a small meeting room on the third floor of the first floor of the material, which is also a lounge, with sofas for short breaks.

When he is usually tired, he will rest there for a while.

Returning to Caiyi with Han Jiaying, he thought that the junior would leave, but unexpectedly she sat down and took out "Semiconductor Physics" from her bag.

"Han Jiaying, I remember you said that the time to come to the laboratory on Thursday is in the morning."

"Yes." Han Jiaying pondered for a while, and then she understood Xu Qiu's meaning. She explained:

"Actually, I have very few courses this semester, so I can stay in the laboratory for a while.

Anyway, there is nothing to do when I go back, and I can study by myself here, and I can also find time to learn experimental operations. "

Xu Qiu recalled that in the first semester of his junior year, he had about 16 credits of courses.

His course selection is relatively average, and he takes about 20 credits per semester in his freshman and sophomore year.

Judging by the tone of the school girl, could it be that she has less than 10 credits for this semester?

"How many credits did you take this semester?"

"8 points, all of which are limited to professional courses taken this semester."

"How much, 8 points?"

Xu Qiu thought he had heard it wrong, but seeing the serious expression on the junior girl, it didn't seem like a fake.