The type of cell/panel you envision when you hear/read the word “solar” or “photovoltaic” is likely rather large and made from silicon. Most of us can recall from our “Rocks for Jocks” (Geology 101) class that silicon is extremely abundant in Earth’s crust. Add one tally to the “pro” column for silicon solar. But undergrad geology probably didn’t focus on the most important part of silicon as it relates to solar, and that is its semi-conductive properties.
How PV Cells Operate
The basic physics behind PV cells is simple: create a negative field, a positive field and some way to get the two to interact and generate a flow of electrons. At a deeper level than that, things get nerdy and cool very quickly.
There are two types of silicon semiconductors: p-type and n-type (sounds like geoscientists named these things). The p-type layer has electron holes in it, and the n-type layer has extra electrons. These layers are placed next to each other, which causes electrons to move from the n-type to the p-type across an area called the depletion zone.
When all the holes in the depletion zone are filled, the p-type side then has negatively charged ions, while the n-type has positively charged ions. The situation is primed: an internal electric field has been created, and when sunlight hits the cell, electrons are ejected, which causes more electrons to come and fill those holes, creating an electric flow.
The sunlight that caused the initial ejection provides the excess energy needed to maintain the flow. The setup creates the pathways for those electrons to travel, and the sun provides the extra electrons. It’s not hard to see why these devices can be inefficient and create extra, wasted heat. Overall, though, it’s a scalable process that can be repeated with various materials.
Taking it Tiny
Different materials have varying levels of conductivity, resiliency and sustainability. Newer solar cells can use carbon or other mineral bases. Some of these carbon-based solar cells are being used to generate solar indoors due, partially, to their lack of resilience to the outside elements. Other competing solar technologies use perovskite cells, which face similar resiliency and some environmental concerns but are cheaper and more efficient than their silicon-based counterparts.
Perovskite is a calcium titanium oxide with an orthorhombic structure, but in the world of photovoltaic cells, the term is often applied to refer generally to any material with the same structure as perovskite. Many perovskites are lead-based, hence their environmental concerns.
Perovskites can absorb a wider range of light than typical solar cells, but they also can decompose when they react with moisture and oxygen or when they spend an extended period of time exposed to light. Another way to read the second part of that sentence is “perovskites can decompose quickly (in days to months) when being used as solar panels.” That, understandably, limits their utilization in solar, but there seems to be motivation to push past those limitations.
Scientists at Oxford have been hard at work printing micro-thin, light versions of solar panels — basically solar films made of perovskites — that could coat almost any building or object in a way that silicon-based PVs cannot (see sidebar). These films could generate up to double the electricity generated by current panels and be produced in much smaller sizes than current solar panels, according to CNN reports. Using past increases in efficiency as a base – previous versions of the film increased from 6 to 27-percent efficiency – researchers believe that these films could help perovskites evolve to deliver efficiencies of more than 45 percent.
While we geoscientists can appreciate the notion that the past is the key to the present, finance folks constantly harp on the fact that past performance is not indicative of future performance, and in general, common sense tells us that physics always wins the day. I’m unsure if extrapolating past efficiencies is a good reason to throw a lot of money at this. That should be based more on the physics, but the innovation is intriguing and, if successful, could potentially have a big impact.
Regardless, opportunities for geoscientists in solar development and innovation abound. It’s been the fastest-growing source of energy for the past 19 years consecutively, and geoscientists’ knowledge of natural materials is hard to match. Plus, not only are geoscientists poised to understand how various natural materials behave, we’re also experts at finding them! We can help solve efficiency and environmental challenges, and we’d benefit from the use of solar films.
Many of us have spent time, or currently spend time, in the field, and we can appreciate the notion of lightweight, renewable power. Imagine the same solar recharge technology that works on your analog watch working on your smart watch, GPS or cell phone. Imagine no more battery packs connected to remote seismic stations! I still recall the “fun” I had helping colleagues carry and bury their battery packs and dig trenches to bury the lines for our work on Hekla. We will see how far scientists can take this new technology.