I Have a Research Support System

Xu Qiu bound a few documents in his hands, and glanced at the content. There is no noteworthy work in the field of organic photovoltaics recently.

Maybe they are all holding back big moves, like Xu Zhenghong's derivatives based on the IDTBR system, it is conservatively estimated that there are two or three AM-level articles on the way.

After putting down the papers, Xu Qiu stood up and reported, a PPT summarizing the gains from yesterday's conference.

Wei Xingsi had already asked for the PPTs of the conference speakers from Gong Yuanjiang, but Xu Qiu hadn't had time to put in the corresponding pictures, they were all in the text version.

First, the two tests Bazan mentioned:

Exciton binding energy, that is, the energy required to split a bound electron/hole pair (exciton) into a free electron/hole. Exciton average diffusion distance, that is, the average distance that a bound electron/hole pair (exciton) moves before recombination to emit light/heat.

These two tests appeared more frequently in the early years, targeting the donor materials in the traditional fullerene system, but they are relatively rare now.

The main reason is that these polymer donor materials are essentially similar to the structure of the D-A conjugated copolymer, so there is not much difference in the two parameters obtained by testing them, and these two experiments are very troublesome to measure.

For various reasons, later researchers gradually became too lazy to carry out these two characterizations, and they could not draw any new conclusions, and it was troublesome to measure them.

The general conclusions for fullerene systems are:

On the one hand, the exciton binding energy of donor materials is generally high, resulting in a relatively low open circuit voltage of organic solar cell devices. Materials with the same band gap may be 0.3 lower than the open circuit voltage of inorganic silicon solar cells or perovskite photovoltaic devices. Volts or so.

What is this concept? Take dry batteries as an example. Inorganic silicon or perovskite is like a normal AA-A battery and AA-A battery. The voltage is about 1.5 volts, while the voltage of organic photovoltaics is only 1.2 volts.

In the case of other conditions being equal, organic photovoltaic devices are born with a photoelectric conversion efficiency of about 20% minus DEBUFF.

On the other hand, the average diffusion distance of excitons is also very short, about 10 nanometers.

This means that the vast majority of excitons can only diffuse for a distance of 10 nanometers after they are generated. If they are farther away, the excitons produced by absorbing sunlight with great difficulty will recombine and become light energy or heat energy again.

This is why organic solar cells cannot use planar heterojunctions for the effective layer like silicon-based and perovskite solar cells, but must use bulk heterojunctions.

Because only by forming a bicontinuous three-phase blend structure and ensuring that each phase region has a dimensional scale at the level of 10 nanometers, can it be ensured that the generated excitons will not recombine in large quantities before they are split and collected by electrodes. .

Once the scale of the phase region is too large, such as more than 20 nanometers, or more than 100 nanometers like a planar heterojunction, the excitons generated by the effective layer in the central part after absorbing light have not had time to diffuse to the interface. Recombined and consumed, causing the central area of ​​the effective layer to become a dead zone, which will not contribute to the improvement of device efficiency, thus superimposing one? % efficiency minus DEBUFF.

Similarly, the short average diffusion distance of excitons also prevents organic solar cell devices from making thick films with a thickness of several hundred nanometers, and can only prepare thin films with an effective layer thickness of about 100 nanometers.

A film of 100 nanometers may only absorb about 80% of sunlight, and the remaining 20% ​​will be directly transmitted and lost. If the film can be made thicker, such as 300, 500, or 800 nanometers, the light absorption may reach More than 99%, the transmission loss can be basically ignored.

The thin-film effective layer of about 100 nanometers once again allows the organic photovoltaic device to superimpose an efficiency of about 20% minus DEBUFF.

Several DEBUFFs are superimposed together. If some losses are lost in the transmission layer, interface, light reflection, etc., the final device efficiency will be very small...

This is why according to the SQ limit, the theoretical limit of the photoelectric conversion efficiency of single-junction solar cells is about 30%, while in the field of organic photovoltaics, it is actually only about 12%, which is really too much to hinder...

However, these theories are based on the traditional fullerene system, that is, only the donor material absorbs sunlight to generate excitons.

For the non-fullerene system that is slowly rising now, the acceptor material will also absorb sunlight. Xu Qiu intends to regain these ancient test methods and use the ITIC material he developed to test the water to see if he can obtain Some new theories come out.

If you can get some subversive conclusions, and then match it with high device efficiency as a confirmation, you will have the opportunity to write a big article.

Next, Xu Qiu continued to introduce the gains he got from Gong Yuanjiang, Lu Changjun, Zang Chaojun and others. Relatively speaking, they were relatively trivial. They were some inspirations that he caught when his thoughts collided and he had a brainstorm while listening to the report.

These inspirations are relatively advanced and are ideas that have not been tried in the group, including: "Preparation of semi-transparent devices using Wu Shengnan's FNIC system", "Preparation of stacked multi-junction solar cells with complementary light absorption systems", "Organic photovoltaic and perovskite photovoltaics in the form of non-multijunction devices", "ternary devices based on two light-absorbing complementary non-fullerene acceptors", etc.

Finally, Xu Qiu introduced another more systematic work from Xu Zhenghong's research group, that is, how their group continuously optimized the ADA non-fullerene acceptor molecule based on the Raodanine A unit structure to obtain the present The IDTBR structure.

Xu Qiu also helped Xu Zhenghong to look forward to it, and then can carry out "introducing fluorine atoms on the BT unit", "replacing the two thiophenes at the end of IDT with benzene rings", "introducing cyano groups into the terminal groups of raodanine", etc. series of optimizations.

Of course, he just said it casually, and he didn't mean to do it himself. Xu Qiu can now make more than a dozen systems, which is enough for him to digest for a while.

While Xu Qiu was reporting, Wei Xingsi also listened carefully. He just glanced at Xu Qiu's PPT on the train before, but didn't look at it carefully.

As a result, the more Wei Xingsi listened, the more startled he became. Although there were only a few short pages of PPT and a dozen lines of text, he had condensed scientific research ideas in nearly ten research directions. According to his understanding of these scientific research ideas, more than half of them Everyone has the opportunity to publish articles, and many ideas have the potential to publish articles in the first district.

Is this the reward of taking Xu Qiu out for a meeting for a day? It's so terrifying...

Wei Xingsi couldn't help recalling Xu Qiu's changes in the past year after joining the research group:

In the beginning, Xu Qiu took the initiative to send an email saying that he would join the research group for an internship. The idea at that time was that he finally hoped for a free labor force.

After a face-to-face interview with Xu Qiu, I learned that Xu Qiu has a GPA of 3.5, and his English scores are also very good.

According to the preliminary judgment, if you cultivate it well, you should be able to contribute three or four articles in the second district. If you are lucky, you may be able to publish one or two articles in the first district.

Then, he let Chen Wanqing take Xu Qiu to familiarize himself with various experiments, and let him take over an unfinished school project, which seemed to be about flexible substrates.

I didn't pay much attention to this matter at first, after all, I am an undergraduate student.

It didn't take long before he took out the project conclusion report, and he even sent an article, which was not bad, and if I remember correctly, it should be "Big Molecules".

Next, Xu Qiu learned the polymerization reaction, developed PCE11 independently, and posted an AM directly in front of Yan Hu's research group at HKU.

At that time, he felt that he should be pure luck. He picked up a mistake. Although this is rare in the field of scientific research, it does happen.

Later, the slap in the face came, 3D-PDI system, Xu Qiu published an NC again, broke the world record in the PDI field, and achieved what I wanted to do but failed.

Although this world record was quickly surpassed by Han Jiaying, if Xu Qiu had only luck, he would definitely not be able to make it this far.

He is really capable, and his scientific research level should be similar to that of me when I was young... Probably?

At this time, I had a plan to let him be the small boss of the research group.

Recently, he crossed the field again, came to the ADA system, and developed the ITIC system with an efficiency exceeding 10%, continuing to create miracles.

I also officially promoted him to the position of the small boss of the research group, and planned to arrange for him to visit abroad for two years after graduation, and then specially hired him to come back to take over my class.

Now, seeing his scientific research ideas emerge in endlessly, it seems that there is no end.

According to this trend, let him take over the hammer class. It is estimated that in a few years, I will follow him...

PS: I asked for a recommendation ticket on Monday, and the two chapters were posted directly, and the third update was at 16:00 in the afternoon.