Solar cells, modeling diffusion current

To obtain a better understanding of the effect of the mobility on the performance of a solar cell, a simplified model is introduced to provide an analytical description of the dependence of the short-circuit on the material parameters of the semiconductor for thin film bulk heterojunction solar cells. The following assumptions are suggested to give separate descriptions of the field current and diffusion current ... 

In conclusion we have shown that the junction current of an organic solar cell measured in the dark cannot be used to interpret data obtained with illuminated solar cells. The current changes from SCLC to diffusion and recombination current when the cell is illuminated. This has allowed us to provide a physical basis for the use of a model, which uses the diode equation for the illuminated solar cells. The model is very successful in interpreting the output characteristics of the illuminated organic solar cells by Brabec and confirmed by us. The true junction dark current (diffusion and recombination current) determined by us remains more than the output current of the illuminated solar cell. Now the two currents do not intersect. This also explains why points of inflexion observed in the current measured in the dark disappear in the output current of the illuminated cell. 

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