July 1, 2011
Currently I am working at Taiwan’s Academia Sinica in the Department of Chemistry, in a lab with about 15 other people. They come in and out of the office area and the lab work stations. Many of the students are working towards their masters/Ph.D in chemistry or chemical engineering, so they attend university and then come into lab to work on their theses. The students are all friendly and kind; though they are shy about their English, they laugh and explain what they know in a mixture of Mandarin/English. Around now, students are studying for their oral presentation of their thesis, but their stress does not affect their friendly disposition.
Professor Jiann-Tsuen Lin placed me under the instruction of post-doctoral fellow Yung-Chung Chen, who has been nice enough to explain the concepts and procedures. He works in both organic photovoltaics and dye-sensitized solar cells. In lab, students work on a range of areas, depending on their background.
My work for the summer is in dye-sensitized solar cells. This lab is testing efficiencies of dye-sensitized solar cells by varying the chemical composition of the dye. The lab has certain base chemicals in stock, and the researchers perform reactions in order to produce a new dye. The researchers then purify and evaporate the mixture, and then create a device using the new dye (which is what I'm currently doing). Another approach that the researchers in this lab are using is to vary the concentration of the dye.
Unlike a regular solar cell that uses p-n junctions, dye-sensitized solar cells are based on the idea that certain dye-stained material can absorb a high amount of sunlight, whose energy thus can be used to complete a circuit. It is drawing attention because it is fairly affordable and able to be hand-made. Here is a a bit about its mechanism: A DSSC has titanium dioxide nanoparticles (TiO2) that have adsorbed a molecular dye. A light photon excites the dye, which injects an electron into the semiconductor TiO2. The electron moves along an external circuit and gets transferred to the counter electrode. To fill in the loss of the electron, the dye reacts with an electrolyte mixture of iodide and triiodide. A voltage results from the energy difference between the excited dye and the electrolyte/counter electrode. The calculation of efficiency is done by dividing the cell’s maximum power (product of max current density and the voltage) by the intensity of the light. On the left is a picture out of my energy conversion principles textbook, which may makes it clearer.
Of course, building one is a bit more elaborate and takes several days. Some researchers synthesize compounds for a testable dye (many terrific steps of chromatography and purification involved), some run the analysis of different dyes’ light absorption, some do the actual assembly of the device (which takes at least 4 days). The end result is finding a percentage of efficiency somewhere around 5-7%, although it is stated in papers that DSSCs reach up to 11%. It’s quite a process. I sheepishly admit that my background is somewhere in between mechanical and civil engineering, so this experience in the chemistry department has made me respect the chemists all the more.
July 14, 2011
Academia Sinica | Taipei, Taiwan
Hello! This entry is a step-by-step process of DSSC production, which spans over a few days.
1. Begin with a 10x10 cm piece of FTO, or fluorine tin oxide, glass. FTO is conductive and gives glass a more squeaky feel. All coating is to be done on the FTO side, and I use a voltmeter to check for a electric potential difference. First, cut the glass into eight 2.5x5 cm pieces. This requires etching a line and hand-breaking it.
2. Wash the glass. These pieces are lined into a tray, lowered into a beaker, then set into a metal box that vibrates. The beaker stays in for 10 minutes per solvent, and there are 4 different solvents.
3. Once the glass slides are out and dried, lay scotch tape onto the horizontal sides of each glass slide. Avoid bubbles!
4. The titanium dioxide comes in a small cylindrical bottle, and it is a viscous clear material. Dab it onto the non-tape portion, then use a glass rod to swipe it across. The rod should not roll over the glass, so the result are clean, straight streaks of clear titanium.
5. The slides are left to dry for two hours, then I remove the tape and place the slides into an oven for 80 degrees Celsius, then place into another heater for over 300 degrees. This whole process takes over 6 hours.
6. Once the first layer is completed, repeat for a second layer, same material.
7. The glass slides need to have a third layer, a diffuse opaque white layer that will noticeably take on the color of the dye. This is another form of titanium dioxide. This layer is also left to air dry and oven dry in the same method.
7. Now the glass can be cut and broken into small ~1.6x2.5 cm slides. Use a weak blade to scrape off the titanium into a 0.5x0.5 cm square that is slightly off center.
8. So how does "DYE sensitized" come in? Once the pieces are ready, they are dipped, titanium face up, into a synthesized or commercial dye and set aside for a few hours in a dark, cool place.
So what's the other half of the solar cell? The counter electrode, of course.
9. The counter electrode begins with 2.5x2.5 pieces of FTO glass. Pipette some platinum solution atop the FTO glass pieces. Let dry for 30 minutes, then transfer them to an oven, then another heater. It cooks at up to 380 degrees for a total of about five hours. By the end of this process, the FTO glass is completely dry, with a smoky tint.
10. Next, apply, with a toothpick, a silver superconductor material along the side of the slide, about 2-4 mm wide. Let dry on a hot plate at about 120 degrees Celsius for about two hours.
11. In order to prevent loss of current due to excessive surface area of the counter electrode, a nonconducting yellow film is placed onto the counter electrode. The yellow sticky film covers all but a small 0.7x0.7 cm window, which will overlap the 0.5x0.5 titanium. Cut out a window, slowly peel off the film from its backing, place it on top of the glass, and slice away the leftover.
A counter electrode can be used several times, whereas every titanium slide is only one-time-use.
For DSSC assembly, I have these two halves (already washed in solvent and then dried), an electrolyte solution, a thin light guard, and two binder clips.
12. Place a few drops of electrolyte, a iodide and triodide solution, onto the counter electrode's open "window." Lower the titanium slide gently onto the top, so that the titanium square meets the "window." This has to be done while preventing any bubbles, because this results to a loss of current and thus loss of efficiency.
13. Dab away the surrounding electrolyte off the sides, so it's clean and dry. Use the light guard in order to cover everything but the little window, and secure it all together with two binder clips.
14. Thus what is left is a handmade, assembled solar cell. Attach an alligator clip onto each of its two edges to complete a circuit. Plug this into the current reader and place it under a light!
This is the physical process of making the solar cell. The next process is determining the voltage, circuit, and incident photon-to-electron conversion efficiency, which is performed by recording data and several calculations. I have just started varying certain factors and collecting information, and I hope to share them soon. Thank you for reading!
Friday, July 29, 2011
Taipei, Taiwan | Academia Sinica | Department of Chemistry
I appreciate the work environment at Academia Sinica; it is a kind of setting I have yet to experience in America. Taiwan has a mandatory military service for every male after high school, but it can be postponed with more education, or it can be replaced with a post-doctoral fellowship. So the lab is filled with undergraduate interns, graduates, phD candidates, or post-doctoral fellows, from age 19 to early 30s. Despite the age differences, the environment is a bit more casual and personal, probably because the space is small and people usually stay full-time. They go out together to lunch, they joke around. I was lucky enough to get to know them on a more personal level, asking about their families and interests. Occasionally professor Jiann Tsuen Lin comes in and chats with an individual about a serious research topic. He makes friendly but indirect requests and suggestions. This is met with more hurrying about to complete a task. Every week, we have a meeting, where about five students present their findings in ten-minute presentations. It is a lab of productivity.
I think the biggest challenge I have is the one that makes this experience the most interesting: the language difference. Everyone in lab, except for the international students, knows both Mandarin Chinese and Taiwanese. They have studied English in middle to high school, but more on being able to read and write it. Thus they say apologetically that their speaking is not as good. Yet interestingly, they immediately understand English words in chemistry - like electrochemistry, ethanol, ligand, solvent, and compound - better than some English-speaking people. My own Mandarin is limited to what I know from my family household, and I can string only a few sentences together. My Taiwanese is even worse. The only things I know how to say in Taiwanese are “I don’t know” (quite intentionally, from Dr. Chen) and “cockroach” (quite frequently, from my mom). So lately, I have been trying to identify and recall Chinese words and use body language. For the more difficult work-related messages, I need to ask around or plug into Google Translate. All these help get my point across. When all else fails, there would always be laughing it off and being nice. I am glad to be in a country that isn’t condescending to foreigners who aren’t so familiar with the language. It makes me sad when Americans get mad at visitors who can’t speak English.
I think my views toward alternative energy and resources have slightly changed. I have been here for almost two months, and it never occurred to me how exhaustive research is. Dr. Chen has been working on organic and dye-sensitized solar cells, but his work has been looking for slow improvements. He has a thousand little solar cell panels he has stashed away after their one time use, in the drawer under the light-emitting machine. Each one is made with a different dye, different soak time, different method of production. All those steps of creating the solar cell boils down to finding that one percentage. Each one is vulnerable to human error or atmospheric disturbance, which can lower its efficiency significantly. The solvent wash may have too much moisture, the titanium surface may have too many airborne particles, the electrolyte may have bubbles in between the glass, the timespan of light exposure is slightly off, etc. Dr. Hsu says that a higher percentage can be deceiving. Plus the difference between 5% and 6% is not very significant, and it is not always consistent or conclusive. It is difficult making a breakthrough in research, and I am unsure as to what that would be for a solar cell.
Although I think this research has been extremely fascinating, I think I would benefit much with more education in chemistry if I were to continue working here; I would understand the composition of the compound, know what properties mean more favorable dye, know how to alternate certain structures. I think my goals in research has made me favor graduate school, since I could continue research and education. Thus I haven’t forgotten my interest in furthering alternative energy. If anything, I have strengthened it by going deeper into its methods.