I Have a Research Support System

Xu Qiu placed the samples in the transfer compartment of the glove box, and took them out in no hurry.

He followed his senior sister to the external quantum efficiency testing equipment, where there is a computer and a black box.

The light-shielding performance of the cabinet in the closed state is very good.

After opening the box, there are light source, lens, power supply, detector, and lifting platform inside, and the light source can emit monochromatic light of different wavelengths.

Chen Wanqing began to demonstrate the operation.

She put the standard silicon cell on the lifting platform, connected it to the power supply and detector, and then adjusted the lens so that the light spot completely hit the surface of the silicon cell.

The standard silicon cell is 10 cm x 10 cm, and the light spot is very small, so there is no difficulty in handling it.

Then turn on the computer, start the test software, and set the parameters.

The scan interval is set to 300-800 nm, and the step size is set to 10 nm,

start testing.

The instrument started running "dang dang dang", and the test results were displayed on the computer in real time.

The abscissa is the wavelength, and the ordinate is the EQE value. Starting from 300 nanometers, a data point is generated every 10 nanometers.

After the test is completed, the software automatically calibrates according to the test results.

"Senior sister, let me do the next operation." Xu Qiu had already watched the operation process in advance through the system video.

"Are you sure? It's not easy to focus the spot when the sample is tested next time." Chen Wanqing said.

"It's okay, don't worry."

"Okay." After Chen Wanqing finished speaking, she gave up the seat to Xu Qiu.

Xu Qiu took out the sample holder from the transfer cabin, with the side of the quartz glass window facing up, placed it on the lifting platform, and connected the probe to the power supply and detector.

Next, focus the light spot of the light source on the battery to be tested.

This step is indeed difficult, because the area of ​​each battery device is only 0.09 square centimeters.

If the light spot is not fully irradiated within this range, the light energy outside the range will be lost, and the final test result will be low.

But Xu Qiu couldn't be bothered, he adjusted the light spots patiently for a while, and started the test.

"You can do this." Chen Wanqing exclaimed.

"It's just the basic operation, not worth mentioning." Xu Qiu waved his hand casually and said, "By the way, why should the area of ​​the battery device be so small? Wouldn't it be good to make a one square centimeter?"

"Because the larger the battery area, the lower the photoelectric conversion efficiency," Chen Wanqing said:

"At this stage, in order to obtain high efficiency, most research groups are working on small areas. The general international practice is 0.09 or 0.04 square centimeters, but there are also more exaggerated research groups that will make devices of 0.01 square centimeters."

"Let me think about it," Xu Qiu thought for a while, then said:

“I get it, the active layer film we spin-coated looks almost uniform to the naked eye, but there are subtle differences in every area.

For example, a device A of 0.09 square centimeters is divided into nine parts A1-A9, and each part has an area of ​​0.01 square centimeters.

The photoelectric conversion efficiency of A1-A9 may fluctuate between 5.0-5.5%, then the final efficiency of A is about 5.25%.

Finally, compare the highest efficiency, the 0.09 large area is about 5.3%, while the 0.01 small area is 5.5%, and it can even fluctuate to a higher value.

Is this the reason, senior sister? "

"Yes, it's almost like this. Now organic photovoltaic is still in the laboratory stage, so there is no unified standard," Chen Wanqing said:

"I also saw a document before, and the title said that the photoelectric conversion efficiency has reached more than 15%, and it turned out that the journal was in the second division of SCI.

I was shocked at the time, even if I can't publish "Nature" and "Science", I can still publish one of their major sub-journals.

Then I read the text carefully and found that it used monochromatic light instead of simulated sunlight, which was just a gimmick in the title. "

…………

Sample testing is over.

The shape of the EQE curve is roughly similar to the light absorption spectrum of the effective layer, and the theoretical short-circuit current density can be calculated through the built-in integral function of the software.

The theoretical result of this sample is 11.96 milliamperes per square centimeter, and the measured result of the J-V curve is 12.05 milliamperes per square centimeter.

The error between the two is between 5%, indicating that the latter test results are credible.

After that, Xu Qiu tested another five sets of devices.

By 5:15 in the afternoon, all tests were completed.

"Sister's prediction is quite accurate, as expected, I don't need to work overtime today." Xu Qiu said.

"Practice makes perfect," Chen Wanqing said, "By the way, what are we going to eat tonight?"

"Why, do you want a treat, senior sister?"

"Didn't I promise you last week?"

"I was just joking at the time. It's so embarrassing, so let's go eat Gelaoguan hot pot."

"OK."

Because it was Friday night, there were quite a lot of people eating hot pot.

Xu Qiu took a number, A65, and there are 12 tables ahead, and the wait is estimated to be about an hour.

During the waiting period, he was not idle and asked Chen Wanqing for advice.

Although reading the literature can also get the answer, but the effect of real person guidance is naturally better.

Engaging in scientific research is a systematic work, and every detail encountered must be figured out, and there is no guarantee that it will be used someday.

Because every data in every test must eventually be transformed into a demonstration of the results. When writing a paper, we can't tell others that we tested a XXX, and the data obtained is XXX, and then stop.

The resulting data must be analyzed and its relationship to the conclusions of the paper discussed.

If it is a relatively abnormal result that cannot be explained, then it should also be explained that "we cannot explain this phenomenon for the time being", but it is okay if this happens once or twice, and if the whole article is "we cannot explain", it will be rejected by the reviewers. Teach to be a man.

"During the test just now, I found that the EQE value of the device we made is below 60% at most wavelengths, while the silicon cell can reach above 80%. Why is this?" Xu Qiu asked.

"Simply put, there are many problems with the P3HT materials currently used and need to be improved.

If you want to expand specifically, you first need to know the process of converting solar energy into electrical energy:

Photons are irradiated by sunlight, and the effective layer composed of photoelectric materials absorbs photons, and electron-hole pairs are generated inside, and then the electron-hole pairs are split into free charges, which are transported in the material and then collected at the electrodes. Eventually a current is formed.

This process is very complicated, and if there is a problem in any step in the process, it will cause a loss of current, and what you see on the surface is that the EQE is low. "Chen Wanqing said.

"I understand," Xu Qiu said, "So people are making improvements based on P3HT. Up to now, the best donor material is PTB7-TH."

"Yes, the field of organic photovoltaics has been developed for 20 years, and the materials have been iterated for many generations, including PTB7-TH. Do you know why it is called this name?" Chen Wanqing asked.

Xu Qiu shook his head, he only knew a name.

Chen Wanqing explained:

"This is a series of materials, where T represents a thienothiophene unit, B represents a benzothiadiazole unit, and P represents a polymer formed by the copolymerization of these two units, so it was originally called PTB.

Later, based on PTB, researchers modified it to obtain PTB2, PTB3, and PTB7.

Then change the benzene ring on a branched chain of PTB7 to a thiophene ring, so an abbreviation of thiophene -TH is added, and the current PTB7-TH is obtained.

Moreover, in the past 20 years, the main direction of improvement is the polymer donor material, and the acceptor has always used the PCBM series.

Perhaps one day in the future, breakthroughs will be made in the field of receptors, which will bring about earth-shaking changes in the field of organic photovoltaics. "