Electical Model And Numerical Study Of Organic Solar Cells

Compared to inorganic solar cells, organic solar cells have attracted great attention due to their advantages, such as fabrication at low temperature, flexibility and low cost. Then the structure of the organic solar cell is developed from the single layer organic solar cell to the bulk-heterojunction organic solar cell. In experiment, a lot of the research is studied. However, the theory research has insufficient study compared to the experiment one. Therefore, it would be restricted to improve the performance of the organic solar cell. Based on this point, the following work has been done in this paper:1. For the type of the contact at the electrode are the ohmic contact and the schottkey one, the numerical model is established for the single layer organic solar cell which is considered the bimolecular recombination. Then the research is studied the effect of carriers mobilities, the energy gap and the distance between the electron and the hole in the exciton on the performance of the device with the ohmic contact. With the schottkey contact, we also studied the effect of the electrode work function, the generation of the exciton, the LUMO energy of the organic layer, the thickness of the organic solar cell and the temperature on the open-circuit voltage, and the effect of the carriers mobilities and the temperature on the short-circuit current density. The concludes are those, Firstly, for the ohmic contact, the improvement of the mobilities of the free electron and the free hole will lead to the increase of the short-circuit current density. However, the improvement of the mobilities of the free electron and the free hole will have little effect on the open-circuit voltage. In order to keep stability to the open-circuit voltage, the mobilities of the free electron and the one of the free hole should be equal. Secondly, for the schottkey contact, both the open-circuit voltage and the short-circuit current are improvement with the decrease of the cathode work function. Thirdly, the short-circuit current is increased with the improvement of carriers mobilities with the same contacts. Finally, the short-circuit current is increased with the improvement of the temperature, however, the open-circuit voltage is decreased with the improvement of the temperature.2. For the bulk-heterojunction organic solar cell, we studied the J-V characteristic, the distribution of the electric potential, the current density, the carrier density and the recombination rate on the condition of the short circuit, the effect of the HOMO energy and the LUMO energy of the donor and the acceptor, the effective voltage and the temperature on the performance of the device with the ohmic contact. Then we studied the effect of the mole mixture ratio on the short-circuit current density Jsc, the open-circuit voltage Voc and the fill factor FF. The conclude is that the Voc, Jsc and FF could be increased with the decrease of the cathode work function with a certain mole mixture ratio.3. For the planar heterojunction organic solar cell, the electrical model is established which contains the effect of the energy barrier between the acceptor and the cathode, the thicknesses of the donor and the acceptor on the distribution of the carrier density, the electric field and the electric potential on the condition of the open circuit, the effect of the incident light intensity, the thicknesses of the donor and the acceptor on the distribution of the carrier density, the electric field, the electric potential, and the short-circuit current on the condition of the short circuit, and the characteristic of the J-V curve. Therefore, the concludes are those:for a given barrier between the anode and the donorΔΦ(?) and the given barrier between the cathode and the acceptorΔΦc, the short-circuit current density and the carrier density are increased with the light intensity. For a given thickness of the acceptor layer, the short-circuit current density first increases due to increased hole density and then decreased due to lowered electric field with the improvement of the thickness of the donor layer. For a given thickness of the donor layer, the carrier density, the electric field and the electric potential decrease with the improvement of the thickness of the acceptor layer, as a result, the short-circuit current density deceases with the increase of the thickness of the acceptor layer. For the characteristic of the J-V curve, the electric field of the interface between the donor layer and the acceptor layer is mainly influenced of the applied voltage, which is also influenced of the carrier density of the interface between the donor layer and the acceptor layer. As a result, those trends can be eventually influenced of the current density.