Minimizing optical losses in bulk heterojunction polymer solar cells

The efficiency that a solar cell can reach is ultimately limited by the number of photons absorbed in its active layer. Bulk heterojunction polymer solar cells are fabricated from a stack of thin film layers, each of which is thinner than a single wavelength from an incident photon within its absorp...

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Bibliographic Details
Published in:Applied physics. B, Lasers and optics Lasers and optics, 2007-03, Vol.86 (4), p.721-727
Main Authors: MOULE, A. J, MEERHOLZ, K
Format: Article
Language:English
Subjects:
Applied sciences
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Conductivity of specific materials
Dissipation
Electronic transport in condensed matter
Energy
Exact sciences and technology
Heterojunctions
Mathematical models
Natural energy
Photoconduction and photovoltaic effects
photodielectric effects
Photons
Photovoltaic cells
Photovoltaic conversion
Physics
Polymers
organic compounds (including organic semiconductors)
Solar cells
Solar cells. Photoelectrochemical cells
Solar energy
Thin films
Wavelengths
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Summary:The efficiency that a solar cell can reach is ultimately limited by the number of photons absorbed in its active layer. Bulk heterojunction polymer solar cells are fabricated from a stack of thin film layers, each of which is thinner than a single wavelength from an incident photon within its absorption band. One consequence of this thin film layer stack is a strong optical interference between the various layers that can change the quantity of light dissipated in the active layer by 50%. Here we use optical modeling to quantitatively calculate the dissipation in each of the various layers as functions of wavelength and layer thickness. Using this information the loss free short circuit current density can be calculated (Jscmax). Optimization of Jscmax leads to direct improvements in the efficiency of the solar cell through improved light dissipation in the active layer. The optical properties for a P3HT:PCBM active layer and a model Lorentzian low band gap spectrum are optimized and ideal fabrication conditions are reported for these materials.
ISSN:0946-2171
1432-0649
DOI:10.1007/s00340-006-2542-1