Chapter 152: Not by luck

　　 Originally, Xu Qiu also planned to have an in-depth exchange with the senior sister about the direction of "non-fullerene derivatives".
　　 did not expect that she just had a preliminary concept.
　　 This is still a discussion.
　　 This situation is very similar to when she proposed to incorporate perovskite materials into the organic photovoltaic system.
　　 At that time, she also only mentioned one concept, and the following content was developed by Xu Qiulai.
　　 However, it is a blessing that the elder sister, who has always been salted fish, is willing to walk out of the comfort zone of the second district.
　　 I can't beat others for this.
　　 Still be silent, right.
　　……
　　 After Xu Qiujiang has revised several articles proposed by the senior sister, he went to the laboratory to find Han Jiaying.
　　 At this time, she is testing the device. Judging from the stacking condition of the nearby substrates, it should be almost finished.
　　 Generally, before device testing, people are more concerned about the protection of the surface of the substrate. Each piece must be face up and neatly arranged.
　　 But for the tested substrates, especially those with low efficiency, they will be placed a lot more randomly, because they may be recycled soon.
　　In the field of organic photovoltaics, the main experimental work is still the synthesis of materials, as well as the preparation of devices and optimization of conditions, both of which have relatively large variables.
　　 As for other aspects of characterization, the experimental operation is relatively fixed. As long as there are no major mistakes, what is measured basically depends on how the researcher analyzes the experimental data.
　　 Therefore, after synthesizing a batch of materials, Han Jiaying's main job now is to prepare and test devices.
　　 "How, are you almost finished?" Xu Qiu asked.
　　 "Come on, I tested the four systems of the brother first, the highest efficiency is 9.8%, not as high as you did before." Han Jiaying said:
　　 "However, the performance change trends of the four systems are basically the same as what you get. As the number of branched carbon atoms increases, the efficiency first rises and then decreases, and the 2OD side chain is the extreme point."
　　 "The trend is the same. It doesn't matter if the efficiency is higher or lower. Besides, you use aluminum electrodes instead of silver electrodes. Low performance is normal." Xu Qiu said:
　　 "So, your two systems, P3T and P5T, have changed the branch chain, and are there any obvious changes in device performance."
　　 "The performance of the P3T system has not changed much. With the shortening of the side chain, the efficiency has increased from 6.20% to 6.42%," Han Jiaying said:
　　 "However, the P5T system has changed significantly. As the side chain becomes longer, the efficiency has jumped from 4.01% to 5.88%."
　　 Xu Qiu thought for a moment and said:
　　"This phenomenon is quite interesting. It seems that for the P5T system, before and after the side chain changes, it happens to be an important critical point, while the P3T system is not.
　　 P5T is somewhat similar to my original P4T system, the latter is the side chain from 2HD to 2OD, the efficiency is greatly improved, and then to 2DT, the efficiency drops slightly. "
　　 "Brother, with this discovery, can I also post an article?" Han Jiaying said.
　　 "I think too much, but I can't, you, I think about articles all day," Xu Qiu said with a smile:
　　" The weight of this discovery is not enough. It only describes a phenomenon, and at most it becomes a description, written in the article.
　　Unless I can analyze the reasons behind this phenomenon, it would be similar in that case, but I don't have this ability now. "
　　 "That's it," Han Jiaying nodded without understanding, and said:
　　 "But I remember Chen Wanqing's senior sister, she planned to do an experiment on the crystallinity of P4T-2OD, which changes with the processing temperature. Isn't that also a description of a phenomenon?"
　　 "Not the same," Xu Qiu said:
　　"Because she can combine light absorption spectroscopy, transmission electron microscopy, atomic force microscopy, grazing incidence X-ray diffraction and other characterization methods for comprehensive analysis.
　　 To put it another way, she can do many representations and tell a complete story, and my discovery is just the beginning of the story. "
　　 "I seem to understand. Looking at the tone of your words at the time, I thought that another article has arrived." Han Jiaying said.
　　 "I just felt it, and I don't mean that I can irrigate it." Xu Qiu smiled.
　　……
　　 school girl continued the experiment, Xu Qiu stood beside her and began to analyze:
　　 At present, it seems that her proficiency in preparing devices is already very high, and she has mastered various instrument operations and several spin coating methods.
　　 And based on his system, the school girl also repeated the efficiency of 9.8%. He did not use silver electrodes at the beginning, and the highest value was only 9.99%, which is not much different.
　　 As for her two systems, P3T and P5T, most of the known experimental optimization methods that can be used, including the introduction of fluorine atoms, regulation of side chains, and true thermal spin coating, are almost used.
　　This shows that the potential of these two systems is exhausted.
　　Unless subversive experimental optimization methods appear again, it can turn things around.
　　 But thinking about it, it’s not easy.
　　 Then, the final result, the device efficiency of P3T and P5T is likely to fluctuate between 6%-8%.
　　 corresponds to the grade of the article, roughly one to two articles in two sections.
　　 There is a high probability that two articles will be published, because almost no one has reported similar molecular structures. Although the structures of P3T and P5T are similar, they are different after all.
　　 If one efficiency is 6% and the other is 7%, it is more appropriate to send 6% first and then 7%.
　　 This is the advantage of doing synthetic experiments by yourself.
　　Because many groups do not do synthesis, then it forms a threshold.
　　As long as the device preparation level is high enough, and the molecular structure is slightly modified, and a similar result is obtained, an article can be published.
　　 From this point of view, Xu Qiu was lucky when he chose to start with the P4T system.
　　 Of course, it's not entirely due to luck.
　　 At that time, he chose the materials, instead of throwing a dice, but the number of points ~ EbookFREE.me ~ also had his own consideration.
　　 First of all, Xu Qiu summarized a set of his own theories based on the DFT results reported in the literature:
　　 In the DFT results, the energy level distribution is generally uniform, which can ensure the conjugation properties of the material and is beneficial to charge transport. The HOMO/LUMO energy levels are respectively concentrated on the D/A unit, which is helpful for exciton separation.
　　 A molecule with this structure will probably perform better.
　　 Then, he used high-order DFT simulations to calculate the four molecules from P2T to P5T, and carefully observed the HOMO/LUMO energy level distribution map of these molecules.
　　 P4T performed the best, followed by P2T, and finally P3T, P5T was worse.
　　 On the whole, the energy level distribution of P4T is relatively uniform, with distribution on each structural unit, and the molecular conjugation is relatively good.
　　 And its HOMO/LUMO energy levels are respectively concentrated on the D unit 2T and the A unit 2TBT.
　　 not only conforms to his theory, but also proves that the performance is really good in practice.
　　 Xu Qiu infers that this situation may be related to the symmetrical structure of P4T.
　　 Relatively speaking, the asymmetric P3T and P5T are worse.
　　 But this theory is not perfect either.
　　 For example, P2T has a symmetrical structure. From the HOMO/LUMO energy level distribution diagram, the conjugation of the molecule is also better, but the performance is the bottom of the four groups of materials.
　　 This shows that there are other factors outside the theoretical framework that have affected the results.
　　 It is difficult for Xu Qiu to analyze the specific impact.
　　 After all, the complexity of materials with hundreds or thousands of atoms on the microscopic scale is unimaginable.