In this paper, a modified equivalent circuit model is proposed to elucidate the electrical behavior of Organic Solar Cells (OSCs). In this way, this single diode model uses a voltage-dependent series resistance to enhance the modeling accuracy while benefiting from the simplicity of the equivalent circuit. The voltage dependency of the series resistance of OSCs is mainly related to internal processes of charge extraction and charge transport. The charge extraction at electrodes is influenced by space charge effect and many other physical parameters including exciton lifetime, dissociation rate, and free carrier recombination.The carrier transport process from donor/acceptor interface to electrodes is governed by its mobility. On the other hand, carrier mobility of organic material depend on field variation. The voltage-dependent series resistance is not often used in the today’s OSC circuit models due to a lack of a reliable field-dependent extraction approach. This proposed model expands its application in finding optimum bias, behavior analysis and efficiency improvement of OSCs. At first, a genetic algorithm curve fitting is applied to the measured current–voltage characteristics to extract the model’s parameters assuming an average constant series resistance. Then a new algorithm is proposed for extracting the voltage-dependent series resistance. Finally, consistency of the extracted field dependent series resistance with previous literature is presented. The results shows that the average mean square errors of the predicted J–V characteristics by the proposed approach for five cells under test is improved by a factor of 106 in comparison with those of a constant value Rs approach. This is the first successful extraction of voltage dependent series resistance of OSCs from DC current–voltage characteristic.

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