DISTRIBUTED RESISTANCE EFFECTS SIMULATION IN CONCENTRATOR MJ SCS USING 3D-NETWORK MODEL

Abstract

A new 3D model for estimating influence of the effects associated with the distributing character of internal resistances in multijunction solar cells has been elaborated. In the model, a cell is divided by area into some number of units, each photoactive junction of which is described by an equivalent circuit consisting of the current source, series resistance, shunting resistance and three diodes with different ideality factors. Two diodes connected with the current source in the forward polarity simulate the injection and recombination mechanisms of the current flow. Including the third diode connected to the circuit in the opposite direction, which simulates the reverse branch of the subcell dark J-V characteristic, allows simulating more correctly the J-V characteristic of multijunction solar cells at their operation in the conditions of the spatial and spectral redistribution of the illumination created by sunlight concentrators due to the chromatic aberration. The J-V characteristic of a GaInP/GaInAs/Ge solar cell under 500X Fresnel lens concentrator has been calculated. Influence of the shape of the reverse branch of the GaInAs subcell dark J-V characteristic and the photoeffect in the tunnel diode on the J-V characteristic of a multijunction solar cell have been estimated. Dependencies of the open-circuit voltage, the fill factor and the efficiency on the concentration ratio for a GaInP/GaInAs/Ge cell have been simulated and compared with measured ones. It has been shown that the 3D model provides the much better accuracy than the non-distributed circuit does: the optimal number of units to divide a multijunction solar cell on ensuring the necessary calculation accuracy has been estimated.