A cluster of bilayer diodes model for bulk heterojunction organic solar cells

To estimate the value of the ideality factor n and the order of reverse saturation current J(0) in the bulkheterojunction (BHJ) P3HT:PCBM based organic solar cells (OSCs), a multitude of experimentally determined light and dark current density-voltage (J-V) curves from literature were fitted with the ideal single diode model and the obtained results were statistically analyzed. The J-V curves of devices with similar structures, dimensions, fabrication parameters, and operation conditions were considered. The same was done for the bilayer (BL) P3HT/PCBM OSCs. Approximately the same parameter values were obtained for both the BHJ and BL OSC devices under illumination (n(L) is an element of [3, 4] and J(0)(L) is an element of [0.1, 0.01]mA/cm(2)). The gathered dark J-V curves were fitted by using the Shockley equation and statistically analyzed. Interestingly, for the dark J-V curves, n(D) is an element of [2, 3] and J(0)(D) is an element of [0.01, 0.001]mA/cm(2) were obtained. The difference between the n values and the order of J(0) under the light and in the dark was discussed and explained by a limited transport in the OSCs active layer and the contribution of photogenerated carriers to the recombination current. The same J-V parameters obtained for both BHJ and BL devices indicate the same underlying physics in both types of OSCs. By modeling the photogeneration and recombination processes at the D/A interfaces and considering the orientation of the D/A domains with respect to the vector of the resulting electric field in the devices, the short circuit current and J(0)(L) were calculated and compared to the experimental data, and a very good agreement was achieved.