| Description |
One of the fundamental limiting factors in photovoltaics is the Shockley-Queisser limit. In a single junction structure most of the incident solar radiation is lost either due to thermalization, or as absorption loss because the energy of the incident photon is lower than the band gap. Tandem cells or multijunction cells do get around this limit but need to satisfy
current matching constraints and are complex structures in some material systems. In this work we use singlet fission as a possible way to get around this limit. Singlet fission is the property exhibited by some materials, tetracene is one, where a singlet splits into two lower energy triplets. The current from these singlets is doubled without any loss in Voc. We have
measured an external quantum efficiency of up to 30-40% in a bilayer junction device, and a singlet fission efficiency of 72% in a tetracene-C60 device that is effectively a blend. The experiment sets the stage for further exploration of higher efficiency bilayer and bulk heterojunction solar cells using singlet fission.
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