Chapter 357: Conjecture, prove it!

This temperature controller is used by Duan Yun to test thermoelectric devices. The accuracy is very high and the heating program is also very fine.
There are three major grades, namely fast, medium and slow.
Each large grade has nine small grades from 1 to 9, corresponding to different heating powers.
If it is 9 gears faster, the heating speed is brushed, if it is 1 gear slow, it may be a snail-like heating speed.
The thermocouple is independently placed next to the sample. In an approximately vacuum environment, heat conduction is very slow, and the temperature display will lag behind the heating operation.
In other words, the main difficulty of the experiment is temperature control.
The heat taken away by the liquid nitrogen in the liquid nitrogen tank and the heat provided by the heater must be offset before the temperature can stabilize.
Of course, it is impossible to achieve complete accuracy.
Certain experimental errors are still acceptable. For example, if the test point is 120K, the temperature fluctuation during the test is between 119.9K-120.1K, which is acceptable.
The actual temperature of the current temperature sensor is 118.74K, and the cooling rate has been very slow, decreasing by 0.01K.
Xu Qiu checked the quartz window, and there was no fog, indicating that the internal vacuum was still relatively high, so he filled up the liquid nitrogen again, and put the cryogenic device into the PL instrument.
From now on, continuous testing is required.
Once it is interrupted in any way, including the liquid nitrogen completely leaking light, the low temperature device is moved, or the quartz window is fogged, the test needs to be restarted, and the previous test data can only be discarded.
For example, for the first time, six sample points from 120K to 145K were tested at 5K intervals. When measuring 150K, the quartz window suddenly became foggy, then the next test result must be inaccurate, and the test must be continued. If this is the case, the final fit may be a curve, which should be a straight line.
Not only that, you cannot start directly from 150K when retesting. You must start from 120K. Otherwise, the previous data will be used. It is very likely that the two sets of data will not match, and there will be a fault at 150K. Now it becomes two straight lines.
Xu Qiu started the heating program, and tested the water with the slowest one with the lowest power. The target temperature was set to 120K.
At the beginning, the temperature was still slowly decreasing. After about a minute, the temperature began to rise by 0.02 and 0.03K.
Xu Qiu secretly rejoiced, it seems that the power of this slow first gear is not small.
However, it is normal to think about it. After all, the interior is now at a low temperature of about 120K. As long as you heat it up a little, the temperature will take off.
Xu Qiu was very patient and watched the temperature slowly climb for five minutes, finally reaching 120K.
The heater automatically stops working, and the residual heat makes the temperature continue to rise a little, then slowly fall, and then slowly rise again, and finally stabilize at about 120K, the deviation value is less than 0.1K, and the working principle is somewhat similar to that of ordinary heating tables. It's just that the progress of this temperature control is higher now.
After the temperature stabilized at 120K for three minutes, Xu Qiu started testing and continuously tested five sets of PL data.
The PL results fluctuate slightly, but the fluctuation range is not large, within 10%.
Continue to heat up, Xu Qiu set the temperature up program to slow 2 this time, after more than four minutes, the temperature stabilized at 125K, he tested five sets of data again.
130K, 135K, 140K...
As the temperature increased, Xu Qiu also continued to increase the heating rate, 3 gears slower, 4 gears slower...
At the same time, he added three additional liquid nitrogen.
In the end, from 1:30 PM to 8 PM, Xu Qiu got data from 120K to 200K, a total of 17 sets of 85 data.
From start to finish, there is almost no chance to breathe. You need to keep an eye on the temperature changes. Even Xu Qiu has dinner in the office next to him.
No way, it takes five minutes to raise the temperature, three minutes to stabilize the temperature, and five minutes to test. This is still an ideal state. If additional liquid nitrogen is added in the middle, the heating rate will be significantly slower.
Fortunately, in the middle of the experiment, there were no incidents such as complete light leakage of liquid nitrogen, movement of the low-temperature device, or fogging of the quartz window, which is considered to be continuous testing.
Of course, before the results of the fitting data are available, it is not completely certain that the experiment will succeed.
In case the test result is extremely unreasonable, it may be that an unknown problem occurred during the experiment.
Xu Qiu turned off the instrument, placed the cryogenic device in a corner, and opened the valve of the liquid nitrogen tank.
Xu Qiu didn't treat the liquid nitrogen in the liquid nitrogen chamber of the cryogenic device for the time being, so he let it evaporate slowly.
In theory, it is not impossible to pour it out directly, but it is not necessary. Anyway, as long as you keep your mouth open, when you come over tomorrow, the liquid nitrogen will definitely run out.
Back at the office, Xu Qiu started processing data.
Fit according to the formula.
The abscissa is 1/kBT, kB is Boltzmann's constant, and T is temperature.
The ordinate is ln(I0/I(T)-1), I0 is the PL intensity at the lowest temperature, and I(T) is the PL intensity at the corresponding temperature.
Because the lower the temperature, the higher the fluorescence intensity, so I0 is the largest in all PL intensity data, I0/I(T) must be greater than 1, and the base of the logarithm is always positive.
There are two ways to calculate I(T). One is to directly take the maximum intensity value of the PL result at a single wavelength, and the other is to integrate the PL intensity in the full wavelength range to obtain the integrated intensity.
In theory, the two results are the same, and the second integration method may have a smaller error.
Xu Qiu thought about it, and chose the first simpler way.
If the fitting result is normal, then everyone is happy. If the fitting result is not normal, try the second method again.
17 groups of 85 PL data, under each temperature condition, take the average after excluding the singularity, and then calculate and linearly fit.
Finally, the of the linear fit is negative 0.117, and the linear correlation coefficient R is 0.98.
It shows that the exciton binding energy of ITIC is 0.117 electron volts, or 117 milli electron volts.
Theoretical analysis is usually more troublesome. It is not like making materials. It is relatively simple and straightforward. The value is as many as it is.
After obtaining the exciton binding energy, further fitting is needed to obtain the curve of the ratio of excitons spontaneously split into free charges with the density of excited states under normal temperature conditions.
This formula is more complicated, involving nearly 10 physical quantities.
Xu Qiu did some operations with reference to the literature...
The final conclusion is: at 300K temperature and normal solar illuminance, that is, the excited state particle density is 1E12 to 1E14 per cubic centimeter, more than 80% of excitons will spontaneously transform into free charges.
"Conjecture, get it!" After seeing the result, Xu Qiu let out a breath of ease, and it was not wasted that he spent a few days checking information and testing, and finally got the result he wanted.
At this time, Han Jiaying and Wu Shengnan were both in Zhangjiang, and Mo Wenlin was doing experiments in the inner laboratory. Only Chen Wanqing was sitting next to Xu Qiu, code word liver article.
After hearing Xu Qiu's movement, the senior sister leaned in curiously, looked at the ORIGN software on Xu Qiu's computer desktop, and asked, "How did the test result today?"
Xu Qiu looked relaxed and said: "I calculated the exciton binding energy of ITIC. The result is 117 millielectron volts, which is the same as my previous prediction. Further analysis shows that under normal working conditions of organic photovoltaic devices, more than 80% The excitons will spontaneously transform into free charges, so that it can be proved why the ITIC series of non-fullerene materials can realize charge transport without a'driving force'..."
"Wow, this is a major discovery." Chen Wanqing immediately heard the importance of this conclusion. Although her experiment was relatively average, she was not much worse than Xu Qiu in literature reading.
The elder sister paused and continued: "I was just guessing before, but now this result is a real hammer, but this conclusion is a bit more physical. What article do you plan to post?"
Xu Qiu calmly said: "I plan to integrate a few highlights and make a big article."
"Big article? NC?" Chen Wanqing tilted her head and said hesitantly: "Couldn't...you want to publish the "Nature" Dazi magazine?"
"Bingo!" Xu Qiu snapped his fingers and explained: "If the exciton diffusion distance test can also get a good conclusion, coupled with a high-efficiency system of 13%, there will be a chance for a wave of "Nature·Energy" "Or "Joule"."
"It turned out to be a new publication, but that would be a better chance," Chen Wanqing nodded first, and then changed her conversation: "However, are you confident that the efficiency of the new system can achieve 13%?"
At present, the highest efficiency system in the group is the school sister's -4F system with an efficiency of 12.3%.
But in fact, Xu Qiu has already achieved 13.5%. Even if it cannot be fully repeated in reality, it should not be difficult for the efficiency of the J2:IDIC-4F system to reach 13%.
Of course, Xu Qiu couldn’t elaborate on this kind of thing. He just found an excuse and said:
The IDIC system performed well before, and the chances of performance improvement after optimization are very high, and the school girls don’t have to develop J2. J3 donor, maybe the efficiency will break through the combination of two."
"Well, UU reading www.uukanshu.com is definitely possible!" Chen Wanqing encouraged, and her heart also hopes that Xu Qiu can go further.
On the one hand, she can have the current academic achievements, and Xu Qiu's help accounts for a large proportion; on the other hand, she also has the meaning of "putting scientific research dreams on Xu Qiu to complete".
During the summer vacation, Chen Wanqing thought for a long time, and finally realized that she was not suitable for continuing to develop in the academic circle.
After choosing the domestic soil museum, the development space is limited. After all, the current situation of the Red Sea in the scientific research circle has been raising the barriers to entry and emphasizing overseas work experience.
As Xu Qiu has achieved remarkable results, it doesn’t matter what you don’t experience overseas naturally. It’s definitely not a problem to stay in school after graduation. But in her current situation, it’s not easy for her to make a difference. Or go abroad to be a visiting scholar for two years.
If you go abroad to find a post-doc, it is basically difficult to meet Xu Qiu's thighs, most likely to be revealed...
This is why she finally found Blue River on the initiative.
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