I Have a Research Support System

This temperature controller is used by Duan Yun to test thermoelectric devices. It has high precision and a very precise heating program.

There are three major grades, namely fast, medium and slow.

Each large grade has nine small grades from 1 to 9, which correspond to different heating powers.

If it is 9 gears faster, the heating speed is just a swipe, and if it is 1 gear slower, it may be a snail-like heating speed.

The thermocouple is independently placed next to the sample. In an approximate vacuum environment, the heat conduction is very slow, and the temperature display will lag behind the temperature rise 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 to stabilize the temperature.

Of course, it is impossible to be completely accurate.

Certain experimental errors are still allowable. For example, if the test point is 120K, then 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 is already very slow, dropping at a rate of 0.01K.

Xu Qiu checked the quartz window and found that there was no fog, indicating that the vacuum inside was still relatively high, so he filled up the liquid nitrogen again, and then put the cryogenic device into the PL instrument.

From now on, continuous testing is required.

Once the test is interrupted in any way, including liquid nitrogen leaking completely, the cryogenic 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 an interval of 5K. When measuring 150K, the quartz window suddenly fogged up. Then the next test results must be inaccurate, and the test was forced to continue. If , the final result of the fitting may be a curve, which should have been a straight line.

Not only that, when retesting, you can’t start directly from 150K, you must start from 120K, otherwise, if you continue to use the previous data, it is very likely that the two sets of data will not match, and there will be a fault at 150K. The old and new data should be in a straight line. Now it becomes two straight lines.

Xu Qiu turned on the heating program, tested the water with the slowest gear with the lowest power, and set the target temperature to 120K.

At the beginning, the temperature was still slowly decreasing, and after about a minute, the temperature began to rise at a rate of 0.02, 0.03K.

Xu Qiu secretly rejoiced, it seems that the power of this slow speed is not small.

However, it is normal to think about it. After all, the interior is currently at a low temperature of about 120K. As long as it is heated a little, the temperature will take off.

Xu Qiu was very patient, and watched the temperature climb slowly for five minutes, and finally reached 120K.

The heater automatically stops working, and the residual heat makes the temperature continue to rise a little, then slowly falls back, then slowly rises, and finally stabilizes at around 120K, with a deviation of less than 0.1K. The working principle is somewhat similar to that of an ordinary heating table. 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 the test and continuously tested five sets of PL data.

The PL results fluctuate slightly, but the fluctuation range is not large, within 10%.

Continuing to raise the temperature, Xu Qiu this time set the heating program to the slow second gear. After more than four minutes, the temperature stabilized at 125K, and he tested five sets of data again.

130K, 135K, 140K...

As the temperature rises, Xu Qiu also continuously increases the heating rate, slowing down by 3 gears, slowing down by 4 gears...

At the same time, he also added liquid nitrogen three times in the middle.

In the end, from 1:30 p.m. to 8 p.m., Xu Qiu obtained data ranging from 120K to 200K, a total of 17 groups and 85 data.

From the beginning to the end, there was almost no chance to breathe, and he needed to keep an eye on the temperature changes. Even Xu Qiu's dinner was solved by eating takeaway 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 midway, the heating rate will be significantly slower.

Fortunately, in the middle of this experiment, there were no incidents such as complete light leakage of liquid nitrogen, removal of the cryogenic device, or fogging of the quartz window, so the continuous test was considered complete.

Of course, before the fitting data results come out, it cannot be completely sure that the experiment will be successful.

If the test results are extremely unreasonable, it may be that there are unknown problems during the experiment.

Xu Qiu turned off the instrument, put the cryogenic device in a corner, and opened the valve of the liquid nitrogen chamber.

Xu Qiu didn't deal with the liquid nitrogen in the liquid nitrogen chamber of the cryogenic device for the time being, and 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 tomorrow comes, the liquid nitrogen will definitely run away.

Back in the office, Xu Qiu began to process the 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 among 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.

Theoretically, the two results are the same, and the error of the second integration method may be smaller.

After thinking about it, Xu Qiu still 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 mean value after excluding singular points, and then calculate and linearly fit.

Finally, the linear fit had a slope of negative 0.117 and a linear correlation coefficient R of 0.98.

It is shown that the exciton binding energy of ITIC is 0.117 eV, or 117 meV.

Theoretical analysis is usually more troublesome, unlike making materials, it is relatively simple and direct, and the value is whatever it is.

After obtaining the exciton binding energy, further fitting is required to obtain a curve of the ratio of excitons spontaneously splitting into free charges versus the excited state density at room temperature.

This formula is more complicated, involving nearly 10 physical quantities.

Xu Qiu referred to the literature for some manipulations...

The final conclusion is: at a temperature of 300K, under normal sunlight illuminance, that is, under the condition that the excited state particle density is 1E12 to 1E14 per cubic centimeter, more than 80% of the excitons will spontaneously transform into free charges.

"Conjecture, proof!" After seeing the result, Xu Qiu let out a sigh of relief. It was not in vain that he spent several days searching for information and testing, and finally got the result he wanted.

At this time, Han Jiaying and Wu Shengnan were both in Zhangjiang, Mo Wenlin was doing experiments in the inner laboratory, and only Chen Wanqing was sitting next to Xu Qiu, writing liver articles.

After hearing Xu Qiu's movement, the senior sister came over curiously, looked at the ORIGN software on Xu Qiu's computer desktop, and asked, "How is the result of today's test?"

Xu Qiu looked relaxed and said: "I calculated the exciton binding energy of ITIC to be 117 millielectronvolts, which is the same as I predicted before. Further analysis shows that under normal working conditions of organic photovoltaic devices, more than 80% The exciton will spontaneously transform into a free charge, which can prove why the ITIC series of non-fullerene materials do not need a 'driving force' to achieve charge transport..."

"Wow, this is an important discovery." Chen Wanqing immediately heard the importance of this conclusion. Although she is relatively average in terms of experiments, she is not much worse than Xu Qiu in terms of literature reading.

The senior sister paused, and continued: "It was just a guess before, but now that the result comes out, it is a real hammer, but this conclusion is more physical, what article are you planning to post?"

Xu Qiu said calmly: "I plan to integrate several highlights and write a big article."

"Big article? NC?" Chen Wanqing tilted her head, hesitantly said, "Could it be... you want to publish the big sub-issue of "Nature", right?"

"Bingo!" Xu Qiu snapped his fingers and explained: "Afterwards, if the exciton diffusion distance test can also get a good conclusion, coupled with a high-efficiency 13% system, there will be a chance to hit a wave of "Natural Energy ’ or ‘Joule’.”

"So it's a new publication, so the chances are better." Chen Wanqing nodded first, and then changed the topic: "However, are you confident that the efficiency of the new system can reach 13%?"

At present, the highest efficiency system on the surface of the group is the IEICO-4F system of the senior sister, with an efficiency of 12.3%.

But in fact, Xu Qiu's has already achieved 13.5%. Even if it cannot be completely repeated in reality, it should not be difficult for the J2:IDIC-4F system to reach an efficiency of 13%.

Of course, Xu Qiu couldn't go into details about this kind of thing, so he made an excuse at random, saying: "The IDIC system performed well before, and the chance of performance improvement after optimization is very high, and the juniors don't want to develop J2, For J3 donors, maybe the combination of two or two can break through the efficiency.”

"Well, it's definitely possible!" Chen Wanqing encouraged, and she also hoped that Xu Qiu could go further.

On the one hand, Xu Qiu's help has contributed a lot to her current academic achievements; on the other hand, she also has a sense of "entrusting Xu Qiu to complete her scientific research dream".

During the summer vacation, Chen Wanqing thought for a long time, and finally realized that she was not suitable for further development in the academic circle.

After choosing a domestic soil blog, the development space is limited. After all, the overall situation in the scientific research circle has been raising the entry threshold and emphasizing overseas work experience.

For someone like Xu Qiu who has achieved outstanding results, it doesn't matter whether he has overseas experience or not. It is definitely no problem to stay in school after graduation, but in her current situation, she can't be high or low. The final outcome is to go abroad to find a postdoctoral fellow. Post, or go abroad as a visiting scholar for two years.

If you go abroad to find a postgraduate student, it is basically difficult to meet Xu Qiu's thighs, and there is a high probability that the original shape will be revealed...

This is also the reason why she took the initiative to find Blue River in the end.