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The “OPV Lab” simulation tool is an educational resource to analyze the operation and performance of organic solar cells. The tool simulates the current-voltage (I-V) characteristics of organic solar cells with bilayer or planar heterojunction configuration. The following procedure is followed to get the I-V characteristics:
1) Optical absorption inside the device is calculated by the transfer matrix method. The absorption profile depends on the complex refractive indices and the thicknesses of various layers in the cell.
2) Exciton diffusion equation is then solved in both donor and acceptor layers. Exciton concentration at the donor-acceptor interface is set to zero with the assumption that exciton dissociation probability is unity and field independent.
3) Charged carrier transport is simulated by the self consistent solution of drift-diffusion and Poisson equation. Generation term in the carrier continuity equation is calculated from the exciton flux at the D-A interface and the recombination of free carriers at the D-A interface is implemented by bi-molecular recombination. We ignore geminate recombination at the interface.
The tool simulates the I-V characteristics and summarizes the solar cell performance matrices such as efficiency, short circuit current, open circuit voltage, and fill factor. The tool also plots the photon absorption profile, charged carrier distribution, electric field, and energy bands inside the active layer for different terminal voltages. Thus, the tool can be used to analyze the effects of the device geometry (e.g. thickness of various layers) and the transport parameters (e.g. exciton diffusion length, mobilities, etc.) on the performance of organic solar cells. The tool can also be used for the optimum device design for a given set of transport parameters.
We encourage the users to first download the tool documentation from the ‘Supporting Documents’ tab at the top of this section and follow the examples discussed in the manual. The familiarity with the basic capability of the tool will allow one to optimize the bilayer structure.
1) B. Ray, P.R. Nair, and M.A. Alam, “Annealing dependent performance of organic bulk-heterojunction solar cells: A theoretical perspective,” Solar Energy Materials and Solar Cells, vol. 95, Dec. 2011, pp. 3287-3294.
2) B. Ray and M.A. Alam, “A compact physical model for morphology induced intrinsic degradation of organic bulk heterojunction solar cell,” Applied Physics Letters, vol. 99, Jul. 2011, pp. 033303-3.
3) A. L. Ayzner, C. J. Tassone, S. H. Tolbert, and B. J. Schwartz, “Reappraising the Need for Bulk Heterojunctions in Polymer−Fullerene Photovoltaics: The Role of Carrier Transport in All-Solution-Processed P3HT/PCBM Bilayer Solar Cells,” The Journal of Physical Chemistry C, vol. 113, no. 46, pp. 20050-20060, Nov. 2009.
4) B. Ray, and M.A. Alam, "Achieving Fill Factor Above 80% in Organic Solar Cells by Charged Interface", IEEE Journal of Photovoltaics, vol. 3(1), 310-317, 2013.