Design of CuIn_1−y Ga _y Se₂/Si_1 − x Ge _x Tandem solar cells with controlled current matching

A tandem solar cell including of CuIn_1−y Ga _y Se₂/Si_1 − x Ge _x was exhibited by integrating a CuIn_1−y Ga _y Se₂ solar cell on a Si_1 − x Ge _x solar cell to achieve a conversion efficiency of about 26% by controlled current matching. Electrical analyses were used to determine the performance parameters of the bottom and top sub-cells. In this work, an experimental Si_0.73Ge_0.27 solar cell has been modelled. The photovoltaic characteristics of the Si_0.73Ge_0.27 solar cell are in good agreement with its experimental counterpart. Afterwards, a copper–gallium–diselenide (CGS)/Si_0.73Ge_0.27 tandem solar cell with 24.1% efficiency has been designed. Additionally, the bandgap combination of CuIn_1−y Ga _y Se/Si_1 − x Ge _x structure has been studied. The findings indicate that CuIn_1−y Ga _y Se/Si_1 − x Ge _x tandem cell with 0.7 < y< 1 and 0 < x< 0.7 can achieve acceptable efficiency and the optimised CGS/Si device with 26.1% efficiency is proposed. In CGS/Si_0.73Ge_0.27 tandem cell, the current matching is obtained when the CGS thickness of the top cell is 1 µm and the Si_0.73Ge_0.27 absorber thickness of the bottom cell is 1.9 µm. The current matching condition for this device degrades the fill factor, although increases the current, so the device does not achieve maximum output power.