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Xu Qiu disposed of the substrate that had failed etching, and began to think about the reasons for the failure.

On the one hand, it may be that the etching time is too long;

On the other hand, there may be air bubbles between the adhesive tape and the substrate, or their gap is too large.

Experiment again.

Xu Qiu took three more PEN substrates. After affixing the pattern with 3M electrical tape, he repeatedly pressed the parts of the tape with tweezers to make it fit the substrate as closely as possible.

He then filled three new disposable plastic cups with dilute hydrochloric acid and poured in two spoonfuls of zinc powder.

After waiting five seconds, he put each of the three substrates into a plastic cup and pressed the stopwatch.

Every 40 seconds, take out a piece of substrate, then rinse it with deionized water, and tear off the 3M electrical tape attached to it.

Xu Qiu observed with the naked eye that the substrates with etching time of 40 seconds and 80 seconds had good patterns.

For the substrate with an etching time of 120 seconds, the edge of the ITO pattern was corroded by acid, but compared with the previous experiment, the traces became less obvious.

This shows that the tight fit of the tape and the substrate plays a certain role in preventing the acid from seeping into the bottom of the tape.

The naked eye may be deceiving. In order to ensure the success of the etching, Xu Qiu took out a multimeter from the toolbox to measure the conduction of the etched part on the substrate.

Turn the multimeter to conduction mode, if the resistance between the two red and black test leads is very small, the multimeter will make a beep sound.

After testing, the etched parts of the three substrates are all non-conductive, and the ITO itself is a good conductor, which indicates that the exposed ITO was successfully etched.

Therefore, both conditions of etching time of 40 seconds and 80 seconds are feasible.

Xu Qiu finally chose an intermediate value and etched for 1 minute.

…………

After exploring the experimental conditions, Xu Qiu prepared 12 patterned PEN/ITO substrates.

Although one piece failed in the middle because the tape was not glued firmly, it did not affect the overall situation.

He then cleaned the substrates with isopropanol, dried them with a nitrogen gun, and loaded them into Petri dishes.

In the following spin coating operation, Xu Qiu encountered a new problem.

The PEN substrate cannot be sucked firmly by the platform above the coating machine, and the substrate sometimes flies out directly during the high-speed rotation.

After thinking for a while, Xu Qiu pasted the PEN substrate on a glass piece of the same size, and then spin-coated it.

Solve the problem smoothly.

After coating PEDOT:PSS, Xu Qiu took off the glass slide on the substrate, annealed it at 100 degrees Celsius, and wiped the slide.

Afterwards, he reattached the glass slide to the substrate and passed it into a spin-coated glove box.

After Chen Wanqing saw it, she asked curiously: Xu Qiu, what is this? Is there... a PEN substrate on the glass?

That's right, I have found a way to etch the PEN substrate, wet etching, stick it with 3M tape, and control the time, Xu Qiu said:

A piece of glass is attached below for the convenience of spin coating.

Okay, what effective layer are you going to apply later? Chen Wanqing said.

Senior sister, give me some PTB7-TH solution to use, and tell me the method of spin coating. Xu Qiu said.

The solution is on the heating and stirring table, there should be 500 microliters left, which is enough for you, Chen Wanqing said:

As for the experimental conditions, I'll write them down on a sticky note for you later. It's almost lunch time, so let's do the experiment when you come back after eating.

…………

In the afternoon, before one o'clock, Xu Qiu went into the glove box with his senior sister's post-it note.

There was no way, the spin-coated glove box was very popular, and he was afraid that he would not be able to get the right to use the glove box at half past one.

Xu Qiu took a look at the experimental conditions of the senior sister:

Chlorobenzene solvent, 15 mg/ml, donating to acceptor ratio 1:1, 2000 rpm, 0.5% volume fraction of DIO, no annealing.

It can be used directly, just need to adjust the speed.

During the placement and use of the solution, its concentration will change due to solvent volatilization and other reasons.

Usually, the longer the solution is prepared, the higher its concentration, and the higher the corresponding optimal speed.

Therefore, under normal circumstances, a solution will be rotated at multiple speeds to compensate for the impact of solution concentration changes.

The device making this time is just a preliminary attempt, Xu Qiu has no plan to use up all twelve substrates.

He decided to use only four tablets, two of which were coated with PTB7-TH:PC[70]BM solution and the other two with the previous P3HT:PC[60]BM solution.

The two-piece operation of P3HT is slightly more complicated because it involves thermal annealing and solvent annealing.

The annealing temperature needs to be controlled at 100 degrees Celsius, and at the same time, the adhered glass sheet should be removed during the annealing.

…………

Put the four spin-coated substrates into the evaporation cabin, prepare for the evaporation, and start vacuuming.

Xu Qiu saw that no one was using the spin-coating glove box for the time being, so he planned to prepare a solution according to the best conditions he found in the simulation laboratory.

20 mg per ml, PTB7-TH:PC[70]BM solution of 0.7% volume fraction of DIO+chlorobenzene solvent at ratio of 1:1.3 to acceptor, 1 ml.

As soon as the solution was prepared, Xu Qiu was marking the bottle when Chen Wanqing came over.

Are you preparing a solution, PTB7-TH? Chen Wanqing asked.

Yes. Xu Qiu said.

Chen Wanqing nodded and didn't ask further: How long will it take for you?

I'm ready, do you need my help? Xu Qiu asked.

No, I'll do it myself, I want to make a perovskite solution.

…………

After Xu Qiu evaporated the calcium and aluminum electrodes, he tested the device performance.

Pick up the first piece, which is a PTB7-TH based device.

The efficiency is 6.77%.

Not bad, this value at least shows that the battery device is working normally.

Xu Qiu's psychological expectation for the efficiency of this device is more than 5%, because it is only a school project, as long as the data can be seen in the past, there is no need to pursue high efficiency.

After all, the original intention of on-campus projects is mainly to cultivate students' scientific research thinking, and they don't pay much attention to the output of results. Of course, it is good if there are results.

The second piece, the highest value was 6.92%, slightly improved, but did not break through 7%.

Then, he tested two P3HT devices, and the highest value was 4.13%.

Generally speaking, compared with the glass substrate, the performance of the battery device of the PEN substrate is not too serious.

After all the tests were completed, it was past five o'clock, and it was obviously too late to make another batch of devices today.

At this time, Xu Qiu suddenly thought that the solution he prepared was directly based on the optimal conditions, and it would be hard to explain when it was used directly, so he needed to pretend.

When I came to the glove box, the person inside was Chen Wanqing.

Sister, I'm here to prepare the solution, Xu Qiu said:

I just read your experiment notebook, and there is no regulation of solution concentration and donor-acceptor ratio.

I want to try to find out the optimal conditions in this regard, and I plan to make several more sets of solutions, each with only 200 microliters, and it will not cost too much raw materials.

Okay, I'll be ready soon, wait for me for five minutes. Chen Wanqing agreed without thinking too much.