Learn more about photovoltaics research in the Solar Energy Technologies Office, check out these solar energy information resources, and find out more about how solar works.
Solar Photovoltaic Cell Basics
When light shines on a photovoltaic (PV) cell – also called a solar cell – that light may be reflected, absorbed, or pass right through the cell. The PV cell is composed of semiconductor material; the “semi” means that it can conduct electricity better than an insulator but not as well as a good conductor like a metal. There are several different semiconductor materials used in PV cells.
When the semiconductor is exposed to light, it absorbs the light’s energy and transfers it to negatively charged particles in the material called electrons. This extra energy allows the electrons to flow through the material as an electrical current. This current is extracted through conductive metal contacts – the grid-like lines on a solar cells – and can then be used to power your home and the rest of the electric grid.
The efficiency of a PV cell is simply the amount of electrical power coming out of the cell compared to the energy from the light shining on it, which indicates how effective the cell is at converting energy from one form to the other. The amount of electricity produced from PV cells depends on the characteristics (such as intensity and wavelengths) of the light available and multiple performance attributes of the cell.
An important property of PV semiconductors is the bandgap, which indicates what wavelengths of light the material can absorb and convert to electrical energy. If the semiconductor’s bandgap matches the wavelengths of light shining on the PV cell, then that cell can efficiently make use of all the available energy.
Learn more below about the most commonly-used semiconductor materials for PV cells.
Silicon
Silicon is, by far, the most common semiconductor material used in solar cells, representing approximately 95% of the modules sold today. It is also the second most abundant material on Earth (after oxygen) and the most common semiconductor used in computer chips. Crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice. This lattice provides an organized structure that makes conversion of light into electricity more efficient.
Solar cells made out of silicon currently provide a combination of high efficiency, low cost, and long lifetime. Modules are expected to last for 25 years or more, still producing more than 80% of their original power after this time.
Thin-Film Photovoltaics
A thin-film solar cell is made by depositing one or more thin layers of PV material on a supporting material such as glass, plastic, or metal. There are two main types of thin-film PV semiconductors on the market today: cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). Both materials can be deposited directly onto either the front or back of the module surface.
CdTe is the second-most common PV material after silicon, and CdTe cells can be made using low-cost manufacturing processes. While this makes them a cost-effective alternative, their efficiencies still aren’t quite as high as silicon. CIGS cells have optimal properties for a PV material and high efficiencies in the lab, but the complexity involved in combining four elements makes the transition from lab to manufacturing more challenging. Both CdTe and CIGS require more protection than silicon to enable long-lasting operation outdoors.
How to Get A Cell Free Acrylic Pour
Believe it or not, many fluid artists do not want cells and struggle to achieve a cell-free painting. To understand how to NOT get cells, it is helpful to first understand the science behind getting cells.
David Alfaro Siqueiros could be called the father of acrylic pouring. He was a well-known Mexican muralist who discovered his “accidental painting” technique in the 1930s. He described his technique in a letter:
“When pouring layers of paint, of different colors, they infiltrate into each other. They produce the most magical fantasies and forms that the human mind can imagine.”
Siqueiros believed that the fluid itself created the painting, and he was right! His work (and ours) is a beautiful fusion of art and science.
Siqueiros’ technique for getting cells leverages the Rayleigh-Taylor instability: the instability that happens when fluids (paints) of different densities (lighter and heavier) interact with each other. The pigments in paint are made of materials such as metals, and some are heavier than others. When you mix paint in the same fluid medium the pigments become similarly suspended and interact with each other.
Heavier paints (pigments) sink through colors that are less dense (lighter). When you swipe titanium white (heavy) over phthalocyanine blue (light), it will sink through and create cells. If you did the opposite (blue swiped over white), you probably wouldn’t. Be aware of paint density! If you do not want cells, layer lighter paints on top of heavier paints.
To get an idea about paint densities, you can refer to the paint density information published by Golden for their acrylic paints. Even if you are not using Golden paints, their chart can provide a guide. Paint density won’t vary much across brands. You can always ask your preferred paints’ customer service departments if they provide similar reference materials.
Even if you have been careful to ensure the lighter paints stay on top of paints with a higher density, as you pour and tilt, colors can move, overlap, and interact. Slow tilting and plenty of paint can help minimize this to some degree. In my experience, using thicker paint and an appropriate technique helps keep paintings cell-free.
Also, adding a base layer of paint slicks up the canvas and helps the paint flow without overlapping as much. Some forms of pouring such as puddle pours or tree-ring pours allow greater control over paint interaction and movement. A flip cup is not your best option if you do NOT want cells. If you do not want cells, use a technique that makes cells less likely, experiment to find the best consistency, use enough paint so you don’t have to overtilt, slick up your canvas, and tilt slowly.
If you are going for no cells, air bubbles will be your nemesis. When air bubbles pop, they create little cells that can potentially become big cells. Air bubbles are created when you stir the paint, and you can create an excess if you stir the paint too fast. The air bubbles will dissipate if you allow the (slowly) mixed paints to sit for a day or so. If I mix paint too fast and then pour right away, I get lots of air bubbles. The photo above shows the effects of air bubbles! If you do not want cells, mix your paints slowly and then let them sit 24 hours.
Most people who start out are looking to create cells. We become obsessed with testing various additives, such as silicone, dimethicone, or alcohol. These additives help with the cell process. If you do not want cells, do not use additives like silicone or alcohol.
In my experience, some pouring mediums are better than others if you don’t want cells. I have found that Liquitex makes less cells than floetrol, and I think GAC 800 is the best of all when you don’t want cells. If you do not want cells, experiment with fluid mediums and see what works best for you.
Good luck to all of you on the quest for no cells and/or cells! It may take a bit of experimentation, but isn’t that a huge part of the joy?! Embrace your inner experimental fluid mechanic like Siqueiros! Happy pouring!
Jenny Post discovered acrylic pouring in April 2017 and uses the therapeutic process to help manage the highs and lows of bipolar disorder and work-related stress. She enjoys sharing with and learning from the acrylic pouring community. You can check out her work on YouTube, Instagram, Facebook, and Etsy.
