‘Turbocharging’ silicon PV: MIT scientists scratch the surface of singlet exciton fission
Scientists at the Massachusetts Institute of Technology have developed a device they say could “turbocharge” a single-junction silicon PV cell, pushing the technology beyond its theoretical limit to efficiencies of 35% and higher.
A paper published last week in the journal Nature detailed how scientists at MIT demonstrated how an effect known as singlet exciton fission could be applied to silicon solar cells and could lead to cell efficiencies as high as 35%.
Singlet exciton fission is an effect seen in certain materials whereby a single photon (particle of light) can generate two electron-hole pairs as it is absorbed into a solar cell rather than the usual one. The effect has been observed by scientists as far back as the 1970s and though it has become an important area of research for some of the world’s leading institutes over the past decade; translating the effect into a viable solar cell has proved complex.
In the paper Sensitization of silicon by singlet exciton fission in tetracene, the scientists claimed to be the first group to transfer the effect from one of the ‘excitonic’ materials known to exhibit it, in this case tetracene – a hydrocarbon organic semiconductor, into crystalline silicon. They achieved the feat by placing an additional layer just a few atoms thick of hafnium oxynitride between the silicon solar cell and the excitonic tetracene layer.
“It turns out this tiny, tiny strip of material at the interface between these two systems ended up defining everything,” explained lead author Markus Einziger, a graduate student at MIT’s Center for Excitonics. “It’s why other researchers couldn’t get this process to work and why we finally did.”