Sunshine On My Shoulders: What Can We Expect From Solar Technology in the Next Decade?
Over the years many different technologies have been promised to us—hover boards, flying cars, time travel, to name a few. The present has followed through on these technologies to varying degrees. Energy technology, while always an exciting field––just ask cave people about fire—is creating ever more exciting products. Specifically two emerging solar energy innovations might very well help to brighten our future.
Surface plasmon resonance for thinner photovoltaic cells
Traditional silicon solar cells, the most widely used commercial solar cells, are heavy and cumbersome. They aren’t exactly made for lining the roofs of cars or adding to camping tents, backpacks, or other lightweight, flexible products. A major barrier to making solar cells thinner lies in the limit of the pathlength of the photoactive layer. That is, the amount of surface area over which the light has a chance to interact with the light-absorbing molecules. It’s like running a lint roller over a sweater—the longer the sweater, the more lint the roller will pick up.
Metal nanoparticles present an exciting workaround for this pathlength conundrum.[1,2] When incident light (sunlight) is similar in energy to the surface plasmon resonance energy of a material, the material scatters the light. This scattering increases the effective pathlength without actually increasing the amount of material present. Surface plasmon resonance technology opens up the possibility for having solar cells that are as thin as foil!
Two for the price of one with singlet fission
Those in the solar energy field know about the Shockley-Queisser limit, which states the maximum theoretical efficiency for sunlight incident on a p-n junction photovoltaic cell is 33.7%. The process of singlet fission, or multiple exciton generation, allows researchers to blast through this ceiling to a new limit of ~45% by more efficiently utilizing the energy of blue photons.
To explain how singlet fission works let me start with an analogy. Say Cole is hungry for a snack and goes to the kitchen to get an apple. He finds that there are only very large apples, much too big for his little appetite. Normally, Cole would eat half of this large apple and throw the rest away, which is wasteful. But if Cole was embracing the idea of singlet fission, he would share half of his apple with Mae, so that they both get a snack and none of the apple is wasted. The same idea is true for light––blue photons are very big apples with lots of energy and red photons are smaller apples with enough energy for just one little boy (or one molecule).
The efficiency of a solar cell can potentially be increased by ~33% when molecules that can undergo singlet fission are utilized as part of the photoactive layer. One reason the efficiency is not doubled to 67% is because only the blue photons (big apples) can be shared between molecules.
Who really knows what the future has in store? But maybe we’ll get this much closer to flying cars if we have paper-thin, high-efficiency solar cells.
S. Pillai, M.A. Green, et al. “Surface Plasmon Enhanced Silicon Solar Cells” Journal of Applied Physics, 2007, 101, pp 093105.
Y. Zhang, M. Gu, et al. “Towards Ultra-Thin Plasmonic Silicon Wafer Solar Cells with Minimized Efficiency Loss,” Scientific Reports, 2014.
W. Shockley and H.J. Queisser, “Detailed Balance Limit of Efficiency of p-n Junction Solar Cells,” Journal of Applied Physics, 1961, pp 510-519.
M.C. Hanna, A.J. Nozik, “Solar Conversion Efficiency of Photovoltaic and Photoelectrolysis Cells with Carrier Multiplication Absorbers,” Journal of Applied Physics, 2006, 100, pp 074510.
About the author
Maria Angelella earned her Ph.D. in physical chemistry from the University of California, San Diego. For seven years she studied the photophysical properties of organic dye molecules using pulsed laser systems, and routinely employed chromatographic and mass spectrometry techniques to purify and characterize her samples. Maria is now an account executive with Chempetitive Group’s PR team and in her spare time, performs improv acting at a local theatre.