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Merocyanine/C 60 Planar Heterojunction Solar Cells: Effect of Dye Orientation on Exciton Dissociation and Solar Cell Performance
Author(s) -
Ojala Antti,
Petersen Andreas,
Fuchs Andreas,
Lovrincic Robert,
Pölking Carl,
Trollmann Jens,
Hwang Jaehyung,
Lennartz Christian,
Reichelt Helmut,
Höffken Hans Wolfgang,
Pucci Annemarie,
Erk Peter,
Kirchartz Thomas,
Würthner Frank
Publication year - 2012
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201101697
Subject(s) - materials science , exciton , dissociation (chemistry) , heterojunction , annealing (glass) , merocyanine , molecule , solar cell , organic solar cell , optoelectronics , chemical physics , planar , photochemistry , chemistry , nanotechnology , condensed matter physics , composite material , organic chemistry , computer graphics (images) , computer science , physics , photochromism , polymer
In this study the charge dissociation at the donor/acceptor heterointerface of thermally evaporated planar heterojunction merocyanine/C 60 organic solar cells is investigated. Deposition of the donor material on a heated substrate as well as post‐annealing of the complete devices at temperatures above the glass transition temperature of the donor material results in a twofold increase of the fill factor. An analytical model employing an electric‐field‐dependent exciton dissociation mechanism reveals that geminate recombination is limiting the performance of as‐deposited cells. Fourier‐transform infrared ellipsometry shows that, at temperatures above the glass transition temperature of the donor material, the orientation of the dye molecules in the donor films undergoes changes upon annealing. Based on this finding, the influence of the dye molecules’ orientations on the charge‐transfer state energies is calculated by quantum mechanical/molecular mechanics methods. The results of these detailed studies provide new insight into the exciton dissociation process in organic photovoltaic devices, and thus valuable guidelines for designing new donor materials.