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

Abstract

The practical performance of tandem organic solar cells (TOSCs) has been simulated using the complete model of the Shockley equation, whereby the shunt resistance (R_SH) and photogenerated current (J_ph) of the device are derived. It is found that the R_SH decreases exponentially with increasing J_ph; this is because the increase in 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 enables more efficient TOSCs. The simulations demonstrate that the highest efficiency of a practical TOSC is achieved at an optimized balance between R_SH and J_ph, which can be achieved by adjusting the thicknesses of the active layers in the front and rear cells. With R_SH = 7600 Ω cm² and J_ph = 14.31 mA cm⁻², a possible efficiency of 22% has been predicted for a TOSC at an open-circuit voltage of 1.973 V. The current research suggests that the contradiction between high R_SH and large J_ph is the central issue limiting improvements in the efficiency of TOSCs.