(a) The device structure of a typical polymer bulk-heterojunciton solar cell fabricated in this study. The chemical structures of MEH-PPV and PCBM are also shown. (b) A schematic showing energy levels of various components in the device structure.
(Color online) characteristics of PV devices as a function of active layer thickness (a) under illumination and (b) in the dark (log-log plot). The illumination was supplied by an Oriel solar simulator under a simulated AM condition.
Measured values of short circuit current density in as a function of active layer thicknesses given in nanometers as obtained from curves shown in Fig. 2(a).
The solar cell consists of a stack of thin-film layers sandwiched between air and a semi-infinite substrate. Solar radiation is incident on the substrate from the left, with intensity for each wavelength in the AM spectrum. The electric field of waves traveling to the right are denoted as ; those traveling left . The substrate and air at the back of the device are treated as layers 0 and , respectively.
A comparison of the measured and calculated short circuit current density in as a function of active layer thickness given in nanometers. The solid circles represent the data measured from the curves under illumination shown in Fig. 2(a). The solid curve represents the data calculated from the model.
A comparison between the different models investigated. Model 1 includes optical interference by the transfer-matrix theory as well the exciton dissociation probability. Model 2 ignores optical interference and assumes exponential decay of light intensity, with exciton dissociation probability included. Model 3 includes optical interference but assumes that all excitons are dissociated. Curves marked with (Avg) denote the same model using the averaged value for the optical exciton generation rate
Measured values of (a) fill factor and (b) serial resistivity of polymer solar cells as functions of active layer thickness. The linear fit to the measured data is shown by the solid lines. The series resistance was calculated from the dark characteristics shown in Fig. 2(b) from the relation .
Measured power conversion efficiency (in percent) as a function of active layer thickness for the solar cells. The polynomial fit to the experimental data shown represents a guide to the eye, rather than model results.
The quantities used in fitting the model to the data, as shown in Fig. 5.
Article metrics loading...
Full text loading...