Photoconductivity measurements of the electronic structure of organic solar cells
- 25 April 2011
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 83 (16)
- https://doi.org/10.1103/physrevb.83.165207
Abstract
Experimental and theoretical studies of the electronic structure of bulk heterojunction (BHJ) organic solar cells are reported. The photoconductivity spectral response of the solar cells has a weak absorption band extending from the band-gap energy down to <1~eV due to charge-transfer optical excitation at the interface between the polymer and the fullerene. The low-energy absorption indicates an exponential band tail of localized states and an absorption model based on the one-electron joint density of electronic states accounts for the data. Transient photoconductivity measurements of the carrier mobility exhibit a temperature-dependent carrier dispersion. Data analysis for the particular case of transport in the BHJ structure is developed. A multiple trapping model of the dispersive transport is consistent with localized band tail states having a comparable density-of-states distribution to those observed by optical absorption. Theoretical calculations of the density of states including disorder in the $\pi${}-$\pi${} spacing of the polymer chains also shows exponential band tailing. A density-of-states model is developed from the data and is discussed.Keywords
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