Photoconductivity measurements of the electronic structure of organic solar cells

• Physical Review B

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 band tailing and an absorption model based on the one-electron joint density of states accounts for the data. Transient photoconductivity measurements of the carrier mobility exhibits temperature-dependent carrier dispersion. A multiple trapping model shows that the data is consistent with localized band tail states having a comparable density of states distribution to those observed by optical absorption. First principles calculations of the effects of disorder in the ?-? distance also shows similar band tailing. The evidence for strong or weak phonon coupling is discussed.

citation

Street, R. A.; Song, K. W.; Northrup, J. E.; Cowan, S. Photoconductivity measurements of the electronic structure of organic solar cells. Physical Review; 2011; B83: 165207.