Effect of band gap on the performance of AlGaAs/GaAs dual junction solar cell

We simulate a dual junction solar cell constructed of Al x Ga 1−x As/GaAs with GaAs as the tunneling diode, and study its performance by varying the band gap of Al x Ga 1−x As. The simulation is performed using industry standard software package ATLAS SILVACO, and the band gap is varied by changing the mole fraction x. The basic parameters such as open circuit voltage, short circuit current, maximum power, and efficiency are studied as a function of x. It is found that the values of short circuit current and open circuit voltage increase almost linearly with mole fraction. With increasing x, the band gap of Al x Ga 1−x As increases. That is, the short circuit current improves with increasing band gap of Al x Ga 1−x As, which is opposite to a single junction solar cell. The efficiency of the dual junction cell also increases with x and reaches a maximum value of 34.4%. However, the improvement is observed up to the x value of 0.45 (direct gap), after which the band gap of Al x Ga 1−x As becomes indirect and the efficiency falls off with increasing x.