The Waterloo Institute for Nanotechnology (WIN) presents a seminar by Dr. Bruno Ehrler, from the Hybrid Solar Cells Group, AMOLF, Science Park, Amsterdam, Netherlands
Beyond solar cell efficiency limits with down conversion and tandem solar cells
Silicon solar cells dominate the photovoltaic market, but their efficiency is already close to the thermodynamic limit. For further efficiency increase, fundamentally new solutions are urgently needed. Tandem solar cells, where two solar cells of different bandgap are stacked onto each other can already reach higher efficiency, and the new hybrid perovskite materials have been proposed as a cost-competitive solution together with conventional silicon solar cells. We performed pressure experiments on perovskite films to study the unusually slow charge recombination, and find that its origin could lie in the band structure. I will further show from efficiency simulations of realistic perovskite/silicon tandem cells, that the efficiency of the perovskite cells needs to be significantly improved before the perovskite/silicon tandem cell outperforms the silicon cell alone.
A promising alternative to tandem cells is the down-conversion of high-energy photons to twice as many lower-energy excited states (excitons). Contrary to tandem solar cells, down-conversion avoids the need for current matching, is much easier to fabricate, and it could enhance the efficiency by a quarter. Singlet fission in organic molecules is seen as one of the most promising mechanisms for down-conversion. I will show the recent developments towards singlet fission parallel tandem solar cells, and direct injection of triplet exciton energy into silicon to enhance its efficiency. I will also outline the challenges remaining for making singlet fission cells a competitor to tandem solar cells.
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