Determining the shunt resistance and photogenerated current of tandem organic solar cells via simulating their practical photovoltaic parameters

The practical performances of tandem organic solar cells (TOSCs) have been simulated via the full model of Shockley equation, whereby the shunt resistance (R SH ) and photogenerated current (J ph ) of device are derived. It is found that the R SH decreases exponentially with the J ph increasing; this is because the increase of J ph increases the vibrational free volumes of the active layers in the front and rear cells, thereby markedly decreasing the R SH . The larger R SH makes the possible bigger efficiency of TOSCs. It is shown by the simulations that the highest efficiency of a practical TOSC is achieved at the optimized balance between R SH and J ph by adjusting the thicknesses of the active layers in the front and rear cells. With R SH =7600 Ω cm 2 and J ph =14.31 mA cm -2 , a possible efficiency of 22% has been predicted for the TOSC at an open-circuit voltage of 1.973 V. The current research indicates that the contradiction between high R SH and large J ph is the major issue to limit the efficiency improvement of TOSCs.