Numerical Simulation Of Bulk Heterojunction Organic Solar Cells

One of the most important means of solar energy utilization is solar cell. Organic solar cell is the research focus in the field of solar cell, mainly due to their material cost is low and easy to modify, ease of fabrication, and can be made into a large area of flexible devices. Since the birth of organic solar cells, people started to improve the photoelectric conversion efficiency through the ways of experiment and theoretical research.In this paper, we have developed a numerical model based on Koster et al. and specifically analyzed the numerical processing, simulated the current density-voltage characteristics of the P3HT:PCBM bulk heterojunction organic solar cells, as well as distribution of the internal parameters of the device at short circuit and open circuit conditions. In this numerical model, more perfect theory of inorganic semiconductor and bimolecular recombination theory are incorporated. In addition, we mainly discussed the factors effects on short circuit current density and open circuit voltage, such as the exciton generation rate, the polymer bandgap, active layer thickness and temperature.The main results are as follows:(1) For the ideal P3HT:PCBM bulk heterojunction organic solar cells, the short circuit current density is58.36A/m2and the open circuit voltage is0.512V from the current density-voltage characteristics at room temperature. At short circuit condition, the internal electric field is high and the carrier density is low, so that the exciton dissociation probability is high (about50%), carrier recombination rate is low. In this condition, the exciton dissociation probability is the mainly factor which affect the energy conversion efficiency of solar cells. At open circuit condition, the internal electric field is lower and the carrier density is higher than short circuit condition. So that the exciton dissociation probability is lower (about32%), the recombination rate R is higher than short circuit condition.(2) When the exciton generation rate changes within3.0×1027(?)12.0×1027m-3s-1, the short circuit current density and the open circuit voltage increase with increasing the exciton generation rate. Comparatively speaking, it is more significant to affect the short circuit current density; When the bandgap width value changes within1.0～1.60eV, the short circuit current density and the open circuit voltage increase linearly with increasing the polymer bandgap. Moreover, the difference is0.49between the open circuit voltage and the bandgap width value; When active layer thickness changes within80～200nm, the distribution of the short circuit current is parabolic with increasing the active layer thickness, it is maximum when the active layer thickness was near160nm. However, the open circuit voltage decreases with increasing the active layer thickness. When temperature changes within280～330K, the short circuit current density increases linearly with increasing the temperature. But the open circuit voltage decreases as the temperature increasing. Within240to400K, the open circuit voltage drops about0.65mV with the temperature rising per1K.(3)We can find out the influence of different factors on the short circuit current density and the open circuit voltage. On one hand, we can directly simulate the short circuit current density changing by writing the program, and we can calculate the open circuit voltage through the testing value method. On the other hand, we can find out the relationship between the short circuit current density or the open circuit voltage and different factors through simulating the change of the current density-voltage characteristics. The results are consistent through different methods, but different methods have their respective advantages and disadvantages.