Singlet fission photovoltaics

The efficiency of a solar cell is restricted by the "single junction limit," whereby photons with energy higher than the bandgap lose energy by thermalization. Singlet exciton fission splits a high-energy molecular excitation ("singlet" exciton) into a pair of lowenergy ones ("triplet" excitons). In solar cells, it promises to generate two electrons per photon, potentially overcoming the singlet junction efficiency limit. In this thesis, we present singlet-fission-based photovoltaic cells that generate more than one electron per photon. We first demonstrate organic photodetectors with quantum efficiencies reaching 100% by exploiting singlet exciton fission. Through study of the magnetic field dependence of the fission process, we find an optimum thickness of singlet fission layers that guarantees the nearly 100% conversion of a singlet into two triplets. By employing an exciton blocking layer and a light trapping scheme to the solar cell, we demonstrate the peak external quantum efficiency exceeding 100% in the visible spectrum. It is the first time that any solar cell has generated more than one electron per photon outside the UV spectrum. We also build a simple model that predicts the rate of singlet fission through intermolecular coupling, enabling rational designs of singlet fission molecules and devices. Finally, we propose a future direction-generating three electrons per photon. As a step toward this goal, we demonstrate singlet exciton fission in hexacene, whose energetics may allow a singlet to split into three triplets.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2013

Author dc:creator

• Lee, Jiye

Advisor dc:contributor.advisor

• Marc A. Baldo.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/79496

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/79496