Chapter 388: Wow, I broke the world record again

In the evening, Xu Qiu returned to the bedroom and saw his roommate Sun Yifan sitting at the table with a lamp, rubbing the hearthstone against the computer.
Sun Yifan greeted: "Xu Qiu, come back, did you see the list sent by the instructor? Our direct doctoral students have no human rights. We only have the second prize. The first prize was taken away by the master and doctoral students."
Xu Qiu shrugged and echoed: "Yes, I thought we were the first prize... But the first and second prizes are about the same. It is estimated that the difference is only one or two thousand yuan at most, sprinkling water."
"That's true," Sun Yifan nodded and asked casually, "By the way, Xu Qiu, did you apply for the National Award? I remember you posted a lot of undergraduate articles."
"Well, I have applied." Xu Qiu responded. He watched behind Sun Yifan for a while, the game just started, both sides are 30 blood, can not see what is coming, he has played WAR3, but after Blizzard, including WOW, Hearthstone, etc. have not touched.
Sun Yifan said suddenly: "I heard that Mu Xue, the monitor of our doctoral class, also applied for the National Award."
Xu Qiu was stunned for a moment and asked, "Mu Xue, didn't she come from Qingbei University for a postgraduate study? How did she apply?
Sun Yifan shook his head: "Then I don't know."
The two chatted a few more words. Xu Qiu heard someone coming out of the bathroom outside the bathroom, so he took toiletries and a card to take a bath.
Usually Xu Qiu and Sun Yifan do not communicate much, not as frequent as their roommates in undergraduate years. Of course, it may be because Tao Yan is relatively familiar.
After taking a shower, Xu Qiu went to bed and entered the simulation laboratory.
These days, for translucent battery devices, he has made many attempts in the simulation laboratory, and obtained the results of some preliminary work.
The preparation of semi-transparent devices is not that difficult. The only difference from traditional devices is that the electrodes are replaced with semi-transparent electrode materials, including thin-layer metals, silver nanowires, or ITO.
Among them, the preparation of ITO is too difficult and requires magnetron sputtering and other means, so Xu Qiu only tried spin-coated silver nanowires and vapor-deposited thin metal electrodes.
Previously, Xu Qiu originally thought that silver nanowires could be spin-coated, which could have the advantages of both conductivity and light transmission, and become a perfect translucent electrode material.
However, it was found in actual operation that the result was not ideal.
He used the thin film spin-coated from the silver nanowire solution purchased by Blue River Company. The light transmittance is satisfied, and it looks very transparent, and the conductivity is on the street. The prepared device is directly in the open state.
In order to find out the reason, Xu Qiu used a multimeter to test the resistance of the silver nanowire film and found that its resistance is in the kiloohm level, while the resistance of the ITO electrode is generally on the order of a few ohms, which is three orders of magnitude away. the above.
Later, he further explored, using various electron microscopes such as AFM, TEM, SEM, etc. to observe. Anyway, the electron microscope in the simulation laboratory does not cost money, so he simply used all the tests.
The final result showed that many of the silver nanowires obtained by spin coating were approximately parallel or stacked together, and there were some nanowires that had been broken.
For things like nanowires to have good conductivity, each nanowire must be in good contact with each other to form a grid-like structure.
Therefore, it is easy to understand the low conductivity of the current microstructure. The possible reason is that the silver nanowires are oriented and damaged during the spin coating process.
In order to try to solve this problem, Xu Qiu browsed the small bug website.
It is found that other people have encountered similar problems when spin-coating silver nanowires, including poor conductivity and poor stability, and there is no good solution.
Therefore, Xu Qiu went to consult some documents and found that the common methods for preparing silver nanowire conductive films are blade coating, drip coating, and "slot-die" methods.
The so-called "slot-die" method is a bit like an advanced version of squeegee coating. It is to place a narrow groove at a certain height above the substrate. The effective layer or transport layer solution is continuously injected into this narrow groove. It drips from the groove and falls on the substrate to form a film. Because it is a narrow groove, the thin film formed is also a thin narrow film. At this time, when the solution is dripping, the narrow groove is moved synchronously at a certain rate, so that the solution after dripping can fill the area swept by the narrow groove, that is, a film is obtained.
The difference between "slot-die" and squeegee coating is that squeegee is to drop the solution on the substrate first, while "slot-die" is that the solution is in a narrow groove and then flows out a little bit, so the process is slightly more difficult. .
Xu Qiu's operation is actually a regular procedure when he encounters an experiment failure:
First, infer the possible causes based on experimental phenomena;
Then use a cheap method (multimeter) to initially confirm the reason;
Use expensive methods (various electron microscopes) to confirm the reason. Of course, if there is no money in the group, this step can be omitted;
Then, go to the bug to see if other people have similar situations and how they solved it;
Finally, look through the literature to find a solution or alternative.
These sequences are not completely fixed, and can be adjusted according to actual needs.
In addition, the reason why I have to visit the little bugs first is because this is a Chinese forum about scientific research. There are many big guys. If you can accurately search for the problems that others have solved, you will save a lot of time, similar to the program. Use wheels made by others in the circle.
After all, it takes a lot of time to retrieve SCI papers. In many cases, an hour may have passed. Finally, I found a few related documents, but in the end, they found nothing useful and could not solve the problem.
Of course, not every time through this operation, the problem of experimental failure can be solved.
For example, this time, Xu Qiu acted fiercely, and finally came to the conclusion that A (plan A) rushed to the street.
That is, based on the existing equipment in the laboratory, it is not appropriate to prepare the top electrode of the translucent device with the silver nanowire film method.
However, Xu Qiu did not panic at all.
Because he still has B, he didn’t bother to optimize the silver nanowire preparation process, and gave up temporarily; A, first use the thin-layer metal electrode method, and if necessary, it is not too late to try again.
Before the formal experiment, Xu Qiu made a brief summary of the existing literature on translucent devices.
He discovered that the concept of translucent devices had existed a few years ago, and there were a lot of literature. There were more than ten articles in District One and District Two, many of which were published by YangYang, a large foreign group.
However, there was only a fullerene system before. Although the average transmittance (AVT) in the visible light range can be very high, the highest can even reach 50%, but the efficiency (PCE) has not been improved.
With AVT alone, without PCE, this is almost the same as
as long as there is face, no lining
. For example, 50% AVT with 1% PCE does not make much sense. In the end, photovoltaic devices have to return to the efficiency competition.
At present, the best performing work is a translucent device based on PCE10:PCBM. The efficiency is only 7%, and the AVT is only 25%. The electrodes they use are thin 10-nanometer silver electrodes.
In the formal experiment, Xu Qiu tried three kinds of thin-layer electrodes, which are commonly used gold, silver, and aluminum. The two systems of PCE10:-4F and PCE10:FNIC-4F were used as standard samples to prepare metal electrodes with different thicknesses. The devices range from 5nm to the normal 100nm.
The final result, take the PCE10:-4F system as an example.
Under the condition of electrode thickness of 100 nanometers, gold, silver, and aluminum electrodes have the highest device efficiencies of 12.3%, 12.4% and 12.5%, respectively. The device efficiencies of the three electrodes are equivalent. At this time, the AVT of the device is about 0, that is, the device does not transmit visible light at all.
Under 50nm conditions, the highest efficiencies are 12.0%, 12.1%, and 12.0%, respectively, and the device efficiencies of the three electrodes are still comparable. At this time, the AVT of the device is also approximately zero.
Under the condition of 30 nanometers, the highest efficiencies were 10.8%, 11.0% and 6.2% respectively. The device efficiencies of the three types of electrodes were differentiated. Among them, the device with gold and silver as the electrode had no obvious efficiency decay, while the device with aluminum as the electrode had the efficiency decay More serious. At this time, the AVT of the device has reached 5%-10%, and some visible light can pass through, and the things behind the device can be seen vaguely.
Under the condition of 20 nanometers, the highest efficiencies were 9.4%, 10.2%, and 0%, respectively. The device with gold and silver as the electrode still has no obvious efficiency degradation, while the device with aluminum as the electrode has been disconnected. At this time, the AVT of the device has reached 10%-20%, and some visible light can pass through, and the things behind the device can be seen vaguely.
Under the condition of 10 nanometers, the highest efficiencies were 8.0%, 9.0% and 0%, respectively. Devices with gold and silver as electrodes also began to differentiate, and devices with silver electrodes were more efficient. At this time, the AVT of the device has reached 20%-40%, and a larger part of the visible light can be transmitted through, and the things behind the device can be seen more clearly.
Under the condition of 5 nanometers, the highest efficiencies are 5.3%, 1.2%, and 0%, respectively. The gold electrode device can still maintain a certain device efficiency, while the efficiency of the silver electrode device jumps directly, close to the open circuit. At this time, the AVT of the device has reached 30%-45%, and a larger part of the visible light can pass through, and you can clearly see what is behind the device.
In addition, in the process of decreasing the electrode thickness, the efficiency of the device decreases mainly due to the decrease of short-circuit current density, and the two parameters of open circuit voltage and fill factor remain almost unchanged.
In response to these experimental phenomena:
The level of elementary school students can draw relatively simple conclusions.
Wow, I broke the world record again.
This is also normal. With the resources Xu Qiu currently possesses, it is enough not to choose a certain sub-field. Once a certain field is selected, it also means that the world record in this sub-field is about to change hands.
After all, he has now temporarily become a leader in the large field of organic photovoltaics.
You can think deeply about the level of middle school students.
To prepare a translucent device, the aluminum electrode is a rubbish, and the device is already on the street before the electrode is translucent.
Think about the level of college students.
The current system is better to use silver electrodes. In the more suitable range of 10-20 nanometers, the device performance is the best one. This may be related to the metal material with the best conductivity.
Think about the level of master students.
At a thickness of 5 nanometers, the performance of the gold electrode surpasses that of silver. This shows that the density of the metal electrode can be a very critical factor in the thin layer state.
Because the density of gold is 19.32 grams per cubic centimeter, the density of silver is 10.49 grams per cubic centimeter, while aluminum is only 2.70 grams per cubic centimeter.
The essence of metal conduction is to conduct electrons through the formation of "electron gas" between metal atoms. There is a prerequisite for conduction here, that is, the metal atoms must be continuous without too many omissions.
When the metal film is relatively thick, it does not matter if the density is lower. Anyway, close packing can be achieved approximately. Even if there are occasional defects, there are other metal atom brothers nearby that can be passed on.
When the metal layer is relatively thin, the metal material with low density will be more likely to appear uneven and not dense during evaporation, and defects will occur. As a result, there is no metal atom brother to help. Conduct electrons smoothly, thereby causing a circuit break.
The level of doctoral students can still think about it again.
Compared with opaque metal electrodes, one of the main sources of device performance loss caused by semi-transparent metal electrodes is the decrease in electrode conductivity, which directly affects the electrode’s ability to collect charges, resulting in a decrease in short-circuit current density and ultimately a decrease in device efficiency. .
But there is another source of performance loss, that is, the secondary reflected light from the opaque metal electrode will decrease.
How to understand this?
When sunlight enters the surface of a photovoltaic device, part of the light will be directly reflected, scattered and lost, and part of it will be converted into heat energy and lost, after which the sunlight will reach the effective layer.
A part of the light that reaches the effective layer will be absorbed by the effective layer to form excitons, and then split and transport to form a current, while a part of it will pass through the effective layer and reach the top electrode.
If the top electrode is 100 nanometers thick gold, silver, aluminum, that is opaque, because the metal will reflect light, it will allow this part of the light through the effective layer to return to the effective layer, which is the so-called "two "Sub-reflection" also contributes to the efficiency of the device.
Now that the metal electrode becomes semi-transparent, part of this light will undergo "secondary reflection" and part of it will be lost through the metal electrode.
At the level of Xu Qiu~EbookFREE.me~, he integrated the above and thought of a multilayer thin-layer electrode structure.
The structure of this thin layer of metal is to first vaporize a thin layer of relatively dense gold, such as one nanometer in thickness, and then vaporize silver with better conductivity, such as 10-20 nanometers.
The expected effect that such a structure can produce is:
The ultra-thin gold layer provides a dense nucleation center, thereby reducing the penetration thickness of the silver film into the transmission layer and the effective layer, improving the uniformity of the silver film at low thickness, and ensuring the formation of a continuous silver film, thereby achieving both Thin metal electrode with high transmittance and low resistance.
Of course, analysis is analysis, and the specific results still have to prove everything with practice.
PS: There are three shifts in 4D today, the second shift and the third shift are at 7 and 16 points respectively.
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