Chapter 41: Exam month (middle)

the second week.
　　 Last week, Xu Qiu initially explored the influence of solution concentration and spin coating methods on the photoelectric performance of the device.
　　 This week he intends to study the effects of donor-acceptor mass ratio, solvent additives and annealing on battery efficiency.
　　Because it is in a simulation laboratory, the raw materials do not need money, so Xu Qiu didn't have too much concerns when designing the experiment.
　　 first is the mass ratio of donor to acceptor.
　　According to the literature, most researchers give a ratio between 1:1 and 1:1.5, but a few also have a ratio of 1:2.
Xu Qiu decided to follow most of the people first, so he prepared 3 sets of solutions to maintain the total solute concentration at 20 mg/ml, and the donor-receptor mass ratios were 1:1, 1:1.3, and 1:1.5. 1.5 ml.
　　Because of the 1:1.3 ratio, the amount of giving and receiving is not an integer, so he calculated the quality of the material in advance, and stuck it on the glove box glass with label paper.
　　 followed by solvent additives.
　　 The most commonly used additive is 1,8-diiodooctane, abbreviated as a high boiling point solvent, which can prolong the film forming time of the solution and improve the morphology of the blended film.
　　 In addition, some researchers also use other solvent additives, such as chloronaphthalene.
　　 Xu Qiu finally chose. He set 3 conditions, namely no addition, 1% and 2% by volume fraction.
　　 The reagent bottle he found in the glove box contained copper powder as a stabilizer and deposited under the liquid.
　　 He first avoided the bottom of the reagent bottle with a disposable dropper, carefully sucked about 100 ml of liquid, and transferred it to a 2 ml centrifuge tube for later use.
　　 After the three groups of solutions were completely dissolved, Xu Qiu divided each group of solutions into 3 bottles, each with 0.5 ml, and then added 0, 5, and 10 microliters with a pipette.
　　 The three sets of solutions have thus become nine sets of solutions.
　　 Next is the annealing condition.
　　 According to literature reports, PTB7-TH system generally does not undergo solvent annealing, and some researchers will choose thermal annealing.
　　 So Xu Qiu designed two conditions: no annealing and thermal annealing at 120 degrees Celsius for 15 minutes.
　　 The last is the speed.
　　 The best speed in the last experiment was 3000r.p.m., and the next-level one was 2500r.p.m. Xu Qiu decided to continue to use these two speeds.
　　 He calculated a total of 3322=36 sets of conditions.
　　 If it weren't for fear of the number of samples swelling to hundreds, Xu Qiu would like to make finer adjustments.
　　 But even so, 36 groups are still quite a lot.
　　 He shook his head, stopped thinking, and started experimenting.
　　 spin coating, complete.
The 　　 evaporation machine can only evaporate up to 25 substrates at a time, so it must be done in two parts.
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 volume ratio of solvent additives is 1%, and the speed is 2500r.pm, without annealing. Condition.
　　The efficiency of other devices fluctuates between 5-9%.
　　 Xu Qiu recorded the list of experiment results in the experiment notebook, and then summarized:
　　First, the best quality ratio is 1:1.3, and the ratio change has little effect on the photoelectric performance. This item does not need to be changed temporarily.
　　Second, the efficiency of the device will increase or decrease when the annealing operation is performed, but the efficiency fluctuation range is small, less than 1%, which shows that the annealing or not has little effect on the photoelectric performance of the device. This item does not need to be changed temporarily.
　　 Third, solvent additives have a greater impact on the performance of the device. 1% is the best addition. If it is increased to 2%, the efficiency will be greatly reduced. Therefore, it is necessary to fine-tune the amount of additives added.
　　 Fourth, the optimum rotation speed for the added sample was changed from 3000 to 2500r.p.m. Therefore, it is necessary to further adjust the rotation speed of the added sample.
　　 After summing up, Xu Qiu had two questions.
　　Why only 1% by volume of additives will have such a big impact on the results?
　　Why does the optimal speed change?
　　 After thinking for a while, he felt a little dizzy in his head, and his body was also sending signs of fatigue to him.
　　 High-intensity review and experimentation, the pace is really too fast, life needs relaxation.
　　 Xu Qiu decided to take a stroll on campus.
　　 was walking around, he thought that today is exactly Sunday, the senior sister should be in the laboratory, it is better to check her experiment progress.
　　…………
　　 "Hey, Xu Qiu, why are you here again." Chen Wanqing said.
　　 "It's too tiring to review, come out and stroll around, stop by to see how the senior sister's experiment is doing." Xu Qiu said.
　　 "It's okay, using your method, it turns out that the polymer dissolves very well. I made a batch of devices with the highest efficiency of 7.57%." Chen Wanqing hesitated and said:
　　 "It's just... a little accident happened."
　　 "Accident? You bombed the glove box?" Xu Qiu said.
　　 "It's not so exaggerated," Chen Wanqing said: "I put the solution previously prepared with chloroform on the heating and mixing table, at 90 degrees Celsius."
　　 "Okay, but there is only one milliliter of the solution, 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 at the time, I didn't notice any abnormality 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 the result was originally black gloves. It's now a blue patterned glove."
　　 "It's okay for people to be fine," Xu Qiu remembered his purpose of coming to the laboratory, and asked:
　　 "Senior sister, what are the conditions for ~EbookFREE.me~ now."
　　 Chen Wanqing took out the experiment log and handed it to Xu Qiu, saying: "The conditions are all up, see for yourself."
　　 Xu Qiu took the notebook and found that the best conditions for the senior sister were "15 mg per milliliter, 1:1 ratio to the receptor, 2000 rotation speed, 120 degrees annealing for 15 minutes."
　　 No solvent additives are written, it should be no addition.
　　 Xu Qiu thought, it would be a bit deliberate to directly remind the senior sister to change the concentration or the ratio to the recipient.
　　 It is better to remind me from the aspect of solvent additives, the school sister may be able to answer the two questions I encountered before.
　　 So, he said:
"Senior sister, when I read the literature of the PTB7-TH system these few days, I found that some of them use solvent additives. Adding 1% can increase the efficiency a lot, but if you add 2%, the efficiency will drop sharply. Do you know why."
　　 "You still read the literature for the exam these days." Chen Wanqing said.
　　 "Now I look at the literature for an hour every day, and accumulate more. I feel that there is still a lot to learn." Xu Qiu said.
"Well, I happen to know your question. The boiling point of the solvent additive is higher than that of the original solvent. So in the final stage of the spin coating process, almost only the solvent additive is left, so even a small amount of additive will be correct. The film morphology has a huge impact.
　　 Similarly, the addition amount is from 1% to 2%, which seems to only increase by 1%. In fact, if the volume of the solvent is doubled, the concentration will be doubled, and the natural influence will be significantly different. "
　　 Chen Wanqing finished speaking, and suddenly realized:
　　 "Yes, I can also try adding some solvent additives when preparing the solution."
　　 Xu Qiu nodded in satisfaction, killing two birds with one stone.