Chapter 465: Continuous breakthroughs, the sword points to 17%!

Regardless of the reason behind it, since the current device efficiency has exceeded 16%, the external quantum efficiency EQE curve must be tested.
So Xu Qiu greeted Han Jiaying: "I'll turn on the EQE computer, warm it up, and test it later."
"Good~ brother~" Han Jiaying said in a sweet and greasy voice. When only the two of them were present, the school girl would be more open, and when there were a lot of people, she would be more reserved.
After speaking, the school girl hummed a song happily, "La la la, la la la la, la la la, la la la la...", apparently very satisfied with the 16% efficiency data she got.
Xu Qiu smiled and shook his head, walked to the experimental platform next to him, and turned on the EQE computer.
Before testing the EQE curve of the sample, it is also necessary to connect the circuit to test the EQE curve of the standard silicon cell for calibration.
In fact, if you want to be lazy, you can only test the EQE curve of the best laminate system later, which saves time.
However, from the perspective of data completeness, it is best to test all of them.
Because in case some data is needed later, and it turns out that it was not tested because of laziness before, then it may be necessary to redo all the devices of the entire system and perform the test again.
Moreover, sometimes the required data may not be obtained by making the device once, and it needs to be repeated twice, three times, or even more times.
Especially for articles of the "Science" grade, the requirements for data completeness are very high, and all the original data files need to be uploaded when submitting the manuscript.
For articles like the usual AM, you don’t need to upload the original data, you only need to upload the text file and supporting information.
Xu Qiu naturally did not choose to be lazy, and planned to test all the devices.
The main reason is that he and his schoolgirls are now collaborating on experiments. One is responsible for testing the J-V curve and the other is responsible for testing the EQE curve.
When the same workload is spread out, the time spent is only 60 to 70% of the original time, and it may take more than an hour in total to complete.
And now there are still three hours before twelve o'clock in the evening, there must be too late in time, and there is no need to rush.
Therefore, Xu Qiu has one mind and three purposes.
While operating the EQE computer for testing, while chatting with the school girl, I thought about the reasons for the abnormally high device efficiency data in my mind.
After thinking about it, Xu Qiu discovered that there are two main variables.
On the one hand, it is the change of experiment operator.
Previously, Xu Qiu and Mo Wenlin were mainly involved in the fabrication of laminated devices. This time it was replaced by Han Jiaying.
Although the school girl was also taught by herself, the operation habits should logically be the same as her own, but Xu Qiu could not completely rule out the possibility of this.
After all, there are more or less differences between people.
However, even if it is really a factor in this aspect, it cannot be verified now.
I can only ask the school girl to come over next week and try another batch of devices to see if I can repeat the result.
On the other hand, when Xu Qiu and others are making laminated devices, they usually calculate the time, wait for the evaporation to complete the test directly, there will be no long stay in the middle:
If the test can be completed before 5:30 in the afternoon, then the test will be done in the afternoon;
If it is too late to complete the test in the afternoon and the data is in a hurry, then order a takeaway and work overtime to get the data out;
If the data is not in a hurry, then delay the start time of the evaporation and arrange the expected completion time of the evaporation to after 7:30 in the evening, so that the experiment can be carried out after the break.
In other words, the previous series of processes such as the preparation and testing of laminated devices are continuous.
But this time, the school girl did not test immediately after evaporating the laminated device at more than five o’clock in the afternoon, and then let the vapor-deposited device be placed in the vacuum environment of the evaporation chamber for about four hours, until The test started around nine o'clock in the evening.
In other words, there is a window period of about four hours between the preparation and testing of this batch of devices.
If it were normal, Xu Qiu would definitely not suspect that it was the reason, but now he really couldn't find the reason, so he could only consider the details.
Moreover, the organic photovoltaic device is also quite special, and its effective layer is a multiphase blended bulk heterojunction structure.
Theoretically, once the device is fabricated, as long as it is not under absolute zero conditions, the morphology of the effective layer changes all the time.
Therefore, even if the same device is tested at different times, the results will be different.
It's just that people generally don't think about device performance changes under shorter time scales, and they are usually stored for hundreds or thousands of hours to verify the stability of the device.
Because of the short-term storage of devices, there are too many factors that will be affected and it is difficult to control.
At this time, Xu Qiu suddenly had an idea and recalled an experimental experience that Tian Qing told him about a year ago when he had just joined the research group:
"I vapor-deposited the devices on Friday and stored them in the vapor deposition chamber. I ran over to test on Sunday. The device efficiency was actually higher than usual..."
Since then, other people in the group have done devices for half a day, or one batch in one day;
Tian Qing will have to wait for two days or even three days to complete a batch. Only occasionally when she is interested in experimenting, she will finish the device in one day.
At that time, Xu Qiu didn't pay much attention to Tian Qing's explanation, only that she was making excuses for paddling herself.
Thinking about it now, Tian Qing might not be lying at the time, she did discover a unique experimental phenomenon.
Moreover, the phenomenon she said may also be universal, for example, it is also applicable to laminated devices.
In other words, after the devices are prepared, they are not tested immediately, but placed in the vacuum environment in the vapor deposition chamber for a certain period of time. There is a possibility that the performance of the devices will be improved.
This variable is easier to verify than the previous experimenter's variable.
Xu Qiu started the operation directly in the simulation laboratory, exploring the device performance of different systems, and the changing trend of the time in the evaporation chamber after the evaporation is completed.
Among them, the selected system includes a variety of classic binary single junction systems, PCE10: PCBM, H22: ITIC, etc., as well as the latest several laminated systems.
The storage time ranges from 0, 1, 3, 6, 9, 12, 18, 24 hours...
Next, continue to test.
Except that the efficiency of the first device reached 16.15%, when the seventh device was tested later, a more efficient device appeared again, reaching 16.24%, which surpassed the result of 16.22% in the simulation laboratory.
Moreover, the processing conditions of the seventh device that can be better are not the optimal conditions explored in the simulation laboratory.
This is a better understanding. The optimal conditions in the simulation laboratory are actually for Xu Qiu's experimental operations. Now two new variables have appeared, and the optimal conditions will likely change accordingly.
In the end, Xu Qiu and Han Jiaying worked in the laboratory until 10:50 in the evening, and finally got all the data.
The short-circuit current density obtained by the integration of the EQE curve is basically the same as the result in the J-V curve, and the error is within 5%, indicating that the device performance data is reliable, and the 16% efficiency data is true.
After finishing the experiment, Xu Qiu found that he was not as tired as previously imagined, and he felt more energetic, probably because he was working outside the glove box, and he could also sit on a stool to test.
The school girl's face is a little red, I don't know if it's tired, or it's too excited and happy.
Because there is still some time before the beginning of the movie, the two chose to take a break at 216.
Han Jiaying sat on Xu Qiu's lap and was trapped in Xu Qiu's arms, as if the battery was plugged into the charger.
After charging for more than 20 minutes, the school girl became full of energy again, and she bounced off Xu Qiu's body and said cheerfully: "Next stop, the cinema, let's go to the duck~"
Wujiaochang, Yida Cinema.
Although it was the early morning premiere, there were still many people due to the superimposed New Year's Eve factors.
The main body of the audience is young people, and most likely are students from the surrounding Magic City University or the Magic City University of Finance and Economics.
The name of the movie is "Bump Man vs. Venom". Xu Qiu read the brief introduction of the promotion before:
The main story is that these two opponents, who are as powerful as a divine residence, met in a spectacular war, when the fate of the world was hanging by a thread.
In order to find the true homeland, Bumpman and his protectors embarked on a difficult journey.
Along with them is a young orphan girl... Maria, there is a unique and strong connection between this girl and Bumpman.
But unexpectedly, they met the angry venom on the forcible channel, which caused a series of destruction around the world.
An invisible force caused a huge conflict between Bumpman and Venom, and the mystery hidden deep in the heart of the earth was also revealed.
Then, Xu Qiu and Han Jiaying took a look at the details and found that the plot was roughly as follows:
Bumpman encountered Venom, they fought, and Bumpman was defeated, but he did not die...
Next, after walking through the plot, they met again and fought again. Bumpman was defeated again, but he was not dead...
After several iterations, Bumpman and Venom discovered that there was a big boss behind the scenes secretly manipulating all this.
As a result, Bumpman and Venom became friends, and worked together to overturn the big boss.
In the end, everyone was happy.
The plot is quite satisfactory, but the fighting special effects are very good.
The overall score can still give 7 or 8 points, it is worth seeing.
After the movie ended, everyone ended in an orderly manner.
Xu Qiu and Han Jiaying were holding hands on the university road, pressing down on the road.
When approaching a fast hotel, Xu Qiu glanced at the school girl, and saw that her walking pace seemed to slow down a lot...
So Xu Qiu asked tentatively: "Did you bring your ID card?"
Then, the school girl responded in a low voice: "Hmm..."
The two walked into the Express Hotel, Xu Qiu took the initiative to say: "Boss, come to a big bed room."
"Sorry, there is no room left tonight."
"Should we switch to another one?"
"Great……"
"Boss, come to a big bed room."
"Sorry, the reservation is full."
"boss……"
"It's full. The reservation was full a week ago. Remember to book early next time."
These are all express hotels along the road, all of which have no vacant rooms, not to mention the double-bed rooms, even the standard rooms are fully booked.
Xu Qiu couldn't help sighing inwardly. It seems that others have come prepared. Sure enough, opportunities always favor those who are prepared.
Finally, Xu Qiu and Han Jiaying walked all the way back to school.
Xu Qiu saw the five-star Crowne Plaza next to him and said to Han Jiaying, "Go try your luck?"
The school girl is not shy anymore, she said openly: "Okay."
"Hello, is there any room, standard room is fine?"
"Hello sir, the room is available, but now there is only the presidential room, do you want to move in?"
"how much is it?"
"Hello sir, the presidential room is 1188 soft sister coins for one night."
"... come to one."
...
...
...
(It is said that a few ellipsis means several times, cross it out)
Although there is a three-day holiday on New Year's Day, it does not exist for the scientific research circle.
Because the schedule in the research group is to rest on January 1, 2 Saturday and Sunday, work as usual on Monday, January 3, and make up work on Saturday afternoon, January 8, so it is equivalent to no rest.
January 3, Monday morning.
Xu Qiu had already obtained the two results that he had handed over to the simulation laboratory to explore.
First of all, it is the change trend of the device performance of different systems with the time that it is placed in the evaporation chamber after the evaporation is completed.
The results show that the previous ternary IDIC-M binary COi8DFIC laminate system with the highest efficiency of 16.22%, as the storage time increases, the device efficiency shows a trend of first rising and then falling.
When the storage time is 12 hours, the device efficiency reaches a peak value of 16.66%.
Xu Qiu's first reaction when he saw the results: "Probably, this is the exclusive welfare God left for the paddling experimenters?"
In fact, Xu Qiu didn't find this "placement to get better" experimental optimization method before, and it was largely influenced by organic synthesis experiments.
Because when doing organic synthesis experiments such as the Stille coupling reaction, Xu Qiu found that the faster the reaction speed, the better the final result, so he directly substituted the same idea when making the device.
This also shows that the element of luck in such things as scientific research is really very big.
In addition, in the experimental phenomenon of "situation getting better", in addition to the peak value after being left for 12 hours, the other results are also very interesting.
Xu Qiu found that when the storage time reaches 3 hours, the highest efficiency has been increased to 16.58%.
After extending the storage time, from 6 hours, to 9 hours, and then to 12 hours, the range of efficiency changes is not large, that is, about 0.02%, 0.03%, and this slowly increases.
After that, if we continue to extend the storage time, the efficiency drop is also not large, about 0.02% and 0.03%. It can be considered that the efficiency has stabilized in the short term.
At the same time, the phenomenon of "placement becomes better" is not applicable to all systems.
Xu Qiu studied a total of 17 standard systems, and found that only five of them have an experimental phenomenon of "placement becomes better", another eight systems are "placement becomes worse", and four systems are "placement unchanged." ".
He tried to categorize the systems of "placement becomes better", "placement becomes worse" and "placement unchanged", and then found:
Most of the systems that "placed better" and "placed worse" are systems that have not been annealed after the effective layer is spin-coated, and most of the systems that are "placed unchanged" are systems that have been annealed.
The annealing experiment mainly affects the residual solvent content after the effective layer is spin-coated. If it is not annealed, there will be chlorobenzene with a boiling point of more than 100 degrees Celsius, and solvent additives with a higher boiling point of more than 200 degrees Celsius. The remaining.
Therefore, Xu Qiu believes that the experimental phenomena of "placement becomes better", "placement becomes worse", and "placement remains unchanged" can be attributed to:
In the vacuum environment of the vapor deposition chamber, the volatilization of the solvent remaining in the device affects the morphology of the effective layer.
For chlorobenzene and these solvents, they are not easy to volatilize under normal temperature and pressure conditions.
Under normal temperature and low pressure conditions, it will gradually "run out" from the effective layer of the device and diffuse into the external vacuum atmosphere.
The process of solvent volatilization takes a certain amount of time.
The normal evaporation process lasts only about 2 hours, which is not enough to completely volatilize the residual solvent inside the effective layer.
Now extend this time for more than 3 hours to allow the solvent to evaporate almost completely.
The process of solvent volatilization will also be accompanied by changes in the micro morphology of the effective layer.
If the impact is positive, the result will be "placement becomes better", otherwise, it is "placement becomes worse."
In a device that has undergone an annealing operation, because there is less solvent remaining in the effective layer, it can be considered that there is no solvent volatilization process.
Therefore, the additional storage time has little effect on the performance of the annealing device.
There may be changes when placed for a long time, but the performance in a short period of time is "placed unchanged."
Of course, these are the views put forward by Xu Qiu. Whether they are specific or not can only be tested through continuous experiments.
However, he feels that there is nothing wrong with this theory, at least the experimental results at this stage support his inferences.
Xu Qiu decided to put the experimental operation of "vacuum placement" together with thermal annealing and solvent annealing as a way to optimize the processing technology.
For specific operations, vapor deposition can be completed at night, without opening the vapor deposition chamber, let the substrate stay in the chamber for a "stuffy night", and wait until the next day to come over during the day for testing.
In doing so, it will take longer.
However, in order to improve the performance of the device, it is also a cost worth paying.
The impact on the simulation laboratory is not great, because the number of vapor deposition chambers inside is large enough that different vapor deposition chambers can be recycled for experiments.
On the other hand, the strategy of introducing PCBM into the top battery has also made breakthrough progress.
As a result of the binary IDIC-M ternary COi8DFIC system in the simulation laboratory, the device efficiency has reached 16.83%.
Compared with the 16.22% of the previous ternary IDIC-M binary COi8DFIC system, an increase of 0.61%.
At this stage, this increase is relatively large.
However, it is also normal.
In the previous report of the Li Dan research group of the National Nano Science and Technology Center, the improvement between their binary and ternary systems was also about 1%. It is not surprising that the improvement of 0.61% in laminated devices is reflected.
Now, with the two strategies of "vacuum placement" and "top battery ternary", both have achieved breakthroughs in performance, which can be described as double happiness.
Moreover, these two strategies were independent of each other when Xu Qiu was exploring before.
In other words, if you put them together and look at the current trend, you can say that the sword is pointing at 17%!
Although Xu Qiu felt a little dreamy, in just over a month, he improved the efficiency of the laminated device from the original 10% to the current close to 17%.
But in fact, judging from the results of semi-empirical analysis, it is normal that the performance of the stacked device is significantly higher than that of the single junction device, and the performance of the stacked device is similar to that of the single junction device, which is abnormal.
For example, as of June 16, 2018, the world's highest efficiency records for three-junction and four-junction stacked devices in all photovoltaic systems have reached 44.4% and 46.0%, respectively.
The king of single junction devices, gallium arsenide photovoltaic devices, has a maximum efficiency of only 35.5%, a 10% difference between the two.
The field of organic photovoltaics has been in an abnormal range before. The main reason is that no suitable near-infrared receptor materials have been found.
Now Xu Qiu's team leads the entire field of organic photovoltaics and fills up this vacancy. It is not surprising that a "leap" in efficiency can be achieved.
If it can achieve 17%, it is already very good data.
It seems that 17% of organic photovoltaics is far from the highest record of 46.0% in other photovoltaics, but as long as the cost of the former can be one-third or less of the latter, the actual gap will not be that big.
This is also the reason why researchers have always been keen to study in some fields, although the performance is not good.
PS: A total of 21W+ words were updated in March, with an average of 7000+ words per day. Continue to work hard in April.
PS2: The current monthly ticket is 1819. I did not expect that it will increase by more than 300 votes a day, nearly 400 votes. Now it is less than 200 votes to break two thousand. I look forward to getting up tomorrow morning and you can see that the number of monthly tickets starts with 2... …
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