Determination of the intrinsic diode parameters of polymer solar cells
Cobussen - Pool, E.M.
Polymer solar cells offer a promising low cost alternative in photovoltaics if the expensive ITO electrode can be omitted. Recently an alternative based on highly conductive PEDOT:PSS in combination with current collecting grids was developed.1 Electrical modeling is carried out to optimize the grid pattern in these polymer solar cells. The basic inputs for this type of modeling are the resistivity of the materials, film thicknesses and the diode parameters of the solar cell. The diode parameters are often determined by fitting the experimental current-voltage measurements to a one-diode model. This gives the well-known dark saturation current density (J0), diode ideality factor (n), photocurrent density (JL), shunt resistance and series resistance. However, the fitted parameters do not always correspond with the intrinsic solar cell parameters, i.e. those that correspond to an infinitesimally small diode, but they are actually lumped parameters containing information of the heterogeneity of the system. For this reason, two one-diode fits corresponding to two different systems (in size and geometry) can yield different intrinsic diode parameters. The reason for this can be found in the heterogeneity of the system. We show an approach to determine the so-called intrinsic diode parameters, by fitting the experimental IV curve against a simulated IV curve that is obtained from a model in which the experimental solar cells are explicitly modeled in 3D. This model provides a simple basis to determine the intrinsic solar cell parameters that can be used for the optimization of grid patterns for polymer solar cells.
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