Chapter 115: The other side of school girl

　　 "Xu Qiu, what do you understand?"
　　 "I thought of a way to further improve the performance of the device."
　　 Xu Qiu calmed his mind and said slowly:
　　 "At present, my system has the highest performance of the device under chloroform solvent, which is above 9%, while the performance of the device cold coated with chlorobenzene solvent is very low.
　　Only under the condition of thermal coating with chlorobenzene solvent, the device efficiency can barely be equivalent to that of chloroform solvent, reaching 9%. I have not figured out the reason before.
　　 And the senior sister just mentioned that the temperature of the solution is different during spin coating, 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. The processing temperature during spin coating will significantly affect the microscopic morphology of the film.
　　Senior sister uses chlorobenzene when testing light absorption, right? "
　　 "Yes, all I use are chlorobenzene solvents, and chloroform solvents can't be heated." Chen Wanqing said:
　　 "Does this have anything to do with what you said?"
　　 "Of course it matters, don't worry," Xu Qiu said:
"In the organic photovoltaic system, the ideal effective layer film must have a three-phase structure, including a pure polymer phase, a pure PCBM phase, and a blend of the two.
"If the intrinsic crystallinity of the polymer material is too strong, and it is not suppressed, a very large crystal region will be formed in the obtained effective layer film, thereby squeezing the proportion of the blend phase, which is not conducive to the improvement of device performance. "
　　 "I seem to understand," Chen Wanqing seemed to understand:
　　"You mean that your system can focus on optimizing the blend morphology of the effective layer because of the high crystallinity of the polymer.
　　 So, how do you do it? "
　　 Xu Qiu made an air of "a child can be taught".
　　 After reaping the elder sister's eyes, he explained seriously:
　　 "The crystallization of the polymer is not completed instantaneously, but takes a certain amount of time.
　　In spin coating, that is, during the process of forming the effective layer, the slower the solvent volatilizes and the more time left for the polymer to crystallize, the larger the crystal phase size of the polymer in the resulting blend film.
　　 Let's analyze the two solvents used before.
　　Chloroform is a low boiling point solvent. Even if it is spin-coated at room temperature, the solvent volatilizes quickly, and its film-forming process is also very fast.
"Under such conditions, the degree of crystallization of the polymer phase can be controlled within a reasonable range.
　　 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.
　　 While the chlorobenzene solvent is directly cold coated, the solvent volatilizes very slowly, and the film formation process is also very slow, which leads to a lot of crystalline phases of the polymer, which is the reason for the poor performance of the corresponding device.
　　The thermal coating method, because the temperature is increased, the solvent volatilization speed is increased, the film forming speed becomes faster, the polymer crystal phase is reduced, and the performance is improved.
　　 Although the performance of the device based on chlorobenzene solvent is not as high as that of chloroform, it can be finely controlled by controlling the temperature during the spin coating process. "
　　 "But, I remember you used a chlorobenzene solution at 90 degrees Celsius for hot coating during the test." Chen Wanqing said:
　　 "The boiling point of chlorobenzene is 130 degrees Celsius, so there is not much room for upward adjustment."
　　 "Isn't there still 40 degrees Celsius," Xu Qiu said:
　　" Besides, the main purpose of our previous hot coating method was to accelerate the dissolution of the solution, not for consideration of crystallinity, so the substrate is still a cold substrate.
　　This method is just a pseudo-hot coating method.
　　We can improve this, in addition to heating the solution, the substrate is also heated to the corresponding temperature.
　　 In fact, it is best to use a spin coater with its own platform heating, which can control the substrate temperature, but we do not have that condition. "
　　 "After your job is published, I would like to mention to Teacher Wei that he will most likely agree to buy it." Chen Wanqing said:
　　" By the way, have you ever thought about what journals you want to submit to? If the efficiency can reach 10%, at least one AM can be published. Even if it is only 9%, there is no problem with publishing its big newspaper AEM.
　　 It would be great if this is my job. I can post an AM and the doctor will be complete. "
　　 "Furthermore, let's look at Mr. Wei's opinions. I didn't think about that much. The first thing is to complete the work." Xu Qiu said.
　　 Han Jiaying was listening in the mist.
　　 However, as a student of materials department, AM still knows that the full name of the journal is "Advanced Materials", which is the top journal of materials major.
　　 This elder brother, there is something, as expected, he didn't look away before.
　　……
　　 It's 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 toward the cafeteria mightily.
　　 Small research group, no thorns, get along well with each other, no intrigue, and no obvious superior-subordinate relationship.
　　 It’s just that Xu Qiu and Chen Wanqing have more contact with each other because of experiments.
　　 However, in their leisure time, everyone also activities together, eating together, and it feels like a small family.
　　Wu Feifei looked at Han Jiaying, who was following Xu Qiu and following each other, still a little envious in her heart.
　　 I look at my school girl, and then I look at my younger brother. I only appeared once in a week~EbookFREE.me~ met once.
　　 After dinner, Tian Qing, Chen Wanqing and their graduate students went back to their dorms to rest. Only Xu Qiu and Han Jiaying returned to the laboratory.
　　 This is also the norm, because the graduate students’ dormitory is between the canteen they often go to and the first floor of the material, 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 bedroom, he has to make a big circle, so he usually returns directly to the laboratory after eating.
　　 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 a short rest.
　　He is usually tired, so he will rest there for a while.
　　 and Han Jiaying returned to Caiyi. He thought that the school girl would leave, but he did not expect that she sat down and took out "Semiconductor Physics" from the bag.
　　 "Han Jiaying, I remember you said earlier that the time for coming to the laboratory on Thursday is morning."
　　 "Yes." Han Jiaying pondered for a while, then she understood what Xu Qiu meant. She explained:
　　 "Actually, I have very few courses this semester, so I can spend more time in the laboratory.
　　 There is nothing to do when I go back anyway. I can study by myself here, and I can also take time to learn experimental operations. "
　　 Xu Qiu recalled that in the last semester of his junior year, he had about 16 credits of courses.
　　He chooses courses more averagely, and his freshman and sophomore year are about 20 credits per semester.
　　 Listening to the tone of the school girl, does she have less than 10 credits of elective courses this semester?
　　 "How many credits have you taken this semester?"
　　 "8 points, all are limited to the professional courses taken this semester."
　　 "How much, 8 points?"
　　 Xu Qiu thought he had heard it wrong, but seeing the serious expression of the school girl, it did not seem to be fake.