I Have a Research Support System

the second week.

Last week, Xu Qiu initially explored the influence of solution concentration and spin coating method on the photoelectric performance of the device.

This week he plans to simultaneously investigate the effects of donor-acceptor mass ratio, solvent additives, and annealing on cell efficiency.

Because it is in the simulation laboratory, the raw materials are free, so Xu Qiu didn't have too many worries when designing the experiment.

The first is the donor-acceptor mass ratio.

According to the literature, most researchers give a ratio between 1:1 and 1:1.5, but a few also reach 1:2.

Xu Qiu decided to follow the majority of people first, so he prepared 3 sets of solutions, keeping the total concentration of solute at 20 mg/ml, and the mass ratio of donor and acceptor at 1:1, 1:1.3 and 1:1.5, respectively. 1.5 ml.

Because of the ratio of 1:1.3, the amount of giver and acceptor is not an integer, so he calculated the quality of the material in advance and pasted it on the glass of the glove box with label paper.

Followed by solvent additives.

The most commonly used additive is 1,8-diiodooctane, referred to as DIO, which is a high-boiling solvent that can prolong the film-forming time of the solution and improve the morphology of the blended film.

In addition, some researchers use other solvent additives, such as chloronaphthalene.

Xu Qiu finally chose DIO. He set three conditions: no addition, addition of 1% and 2% by volume fraction.

In the glove box he found DIO's reagent bottle, which had copper powder inside as a stabilizer, deposited beneath the liquid.

He first used a disposable dropper to avoid the bottom of the reagent bottle, carefully sucked up about 100ml of liquid, and transferred it to a 2ml centrifuge tube for use.

After the three groups of solutions just now were completely dissolved, Xu Qiu divided each group of solutions into three equal bottles of 0.5 ml each, and then added 0, 5, and 10 microliters of DIO in sequence with a pipette gun.

Three sets of solutions have thus become nine sets of solutions.

This is followed by annealing conditions.

According to literature reports, the PTB7-TH system generally does not undergo solvent annealing, and some researchers choose thermal annealing.

So Xu Qiu designed two conditions: no annealing and thermal annealing at 120 degrees Celsius for 15 minutes.

Lastly is the speed.

The best speed in the last experiment was 3000r.p.m., and the next level was 2500r.p.m. Xu Qiu decided to continue using these two speeds.

He calculated, a total of 3*3*2*2=36 sets of conditions.

If it wasn't for the fear that the number of samples would expand to hundreds, Xu Qiu would have wanted to make finer adjustments.

But even so, 36 groups is still quite a lot.

He shook his head, stopped thinking about it, and started the experiment.

Spin coating, done.

The evaporation machine can only evaporate up to 25 substrates at a time, so it needs to be done twice to complete.

Finished test.

The highest efficiency is 9.88%.

The corresponding sample is "1.3, 1, w/o, 2500", that is, the mass ratio of PTB7-TH:PC[70]BM is 1:1.3, the solvent additive DIO volume ratio is 1%, 2500r.p.m. speed, no annealing Under conditions.

Other devices have efficiencies that fluctuate between 5-9%.

Xu Qiu recorded the list of experimental results in the experimental record book, and then made a summary:

First, the optimal mass ratio is 1:1.3, and the change of the ratio has little effect on the optoelectronic performance. This item does not need to be changed for now.

Second, the annealing operation will increase or decrease the device efficiency, but the fluctuation range of the efficiency is small, only less than 1%, which shows that whether annealing or not has little effect on the photoelectric performance of the device. This item does not need to be changed for now.

Third, solvent additives have a greater impact on device performance, and the addition of 1% is the best. If it is increased to 2%, the efficiency will be greatly reduced. Therefore, finer regulation of the amount of additives is required.

Fourth, for the sample with DIO added, the optimum rotational speed was changed from 3000 to 2500r.p.m. Therefore, it is necessary to further adjust the rotational speed of the DIO-added sample.

After summing up, Xu Qiu had two questions.

Why does only 1% volume ratio of additives have such a big impact on the results?

Why does the optimal RPM change?

After thinking for a while, he felt a little dizzy in his head, and his body was also sending him signals of fatigue.

The pace of high-intensity review and experiments is indeed too fast, and life needs to be relaxed.

Xu Qiu decided to take a walk around the campus for a while.

Wandering around, he thought that today happened to be Sunday, the senior should be in the lab, why not go and see the progress of her experiment.

…………

"Hey, Xu Qiu, why are you here again?" Chen Wanqing said.

"I'm too tired from studying, let's go out for a stroll, and drop by to see how my sister is doing with her experiments," Xu Qiu said.

"It's not bad. After using your method, the polymer dissolves very well. I made a batch of devices with a maximum efficiency of 7.57%." Chen Wanqing hesitated and said:

"It's just... a little accident happened."

"Accident? You blew up the glove box?" Xu Qiu said.

"It's not that exaggerated," Chen Wanqing said, "It's just that I put the solution I prepared with chloroform on the heating and stirring table at 90 degrees Celsius."

"Okay, but there's only one milliliter of solution, so it shouldn't be a big problem," Xu Qiu said.

"It's really not a big problem, the quality of the bottle is good," Chen Wanqing said:

"When I picked it up, I didn't find anything unusual from the outside, until I unscrewed the bottle cap with my right hand, the boiling solution sprayed out instantly, and I subconsciously blocked it with rubber gloves, and it turned out that the original black gloves Now it's a blue patterned glove."

"It's good that people are fine," Xu Qiu asked, remembering his purpose of coming to the laboratory:

"Sister, what are the conditions for doing PTB7-TH now?"

Chen Wanqing took out the experiment notebook and handed it to Xu Qiu, saying: "The conditions are all on it, let's read it for yourself."

Xu Qiu took the notebook and found that the best conditions for the senior sister were "15 mg per milliliter, donor-receptor ratio 1:1, 2000 rpm, 120-degree annealing for 15 minutes."

No solvent additive is written, so it should not be added.

Xu Qiu thought to himself, if he directly reminded the senior sister to change the concentration or the ratio of receptors, it would be a bit deliberate.

How about reminding me from the aspect of solvent additives, the senior sister may be able to answer the two questions I encountered before.

So he said:

"Sister, when I read the literature of the PTB7-TH system these days, I found that some of them use solvent additives. Adding 1% DIO can improve the efficiency a lot, but when adding 2%, the efficiency will drop sharply. Do you know why?"

"You still read literature during the exam these days." Chen Wanqing said.

"Now I read literature for an hour every day, and the little things add up. I feel that there is still a lot to learn." Xu Qiu said.

"Well, your question I happen to know that the solvent additive has a higher boiling point than the original solvent, so at the end of the spin-coating process, almost only the solvent additive is left, so even a small amount of additive will be harmful. The film morphology has a great influence.

In the same way, if the amount added is from 1% to 2%, it seems that it only increases by 1%. In fact, if the volume of the solvent doubles, the concentration will double, and the natural impact will be significantly different. "

After Chen Wanqing finished speaking, she suddenly realized:

"Yes, I can also add some solvent additives when preparing the solution."

Xu Qiu nodded in satisfaction, killing two birds with one stone.