Design of two and four-terminals InGaP/GaAs//Si tandem solar cells

Solar cells based on silicon dominate the current market, but its single junction conversion efficiency will never exceed 30%. However, it is possible to surpass this limit by coupling silicon solar cells with III-V multi-junction solar cells; for example, a combination of materials such as InGaP/GaAs or AlGaAs/GaAs on a silicon-based solar cell. In this work, by using a simple model, developed before, the efficiencies of InGaP/GaAs/Si- HJ solar cells with two and four-terminals are calculated. As expected, the four-terminals configuration would provide the highest efficiency since the bandgaps of the involved semiconductors are not optimum for a two-terminals configuration. The expected practical efficiencies at 1 sun (AM1.5 spectrum) for a four-terminals tandem cell can be as high as 41.7%, when the appropriate thickness for each layer, including the anti- reflection coating, are used. In the case of Al 2 O 3 as ARC, the optimum thickness is 88 nm, while the optimum InGaP thickness is 260 nm and GaAs optimum thickness is 1100 nm. The results shown here can be compared with the experimental efficiency around 35.9%, achieved recently for this kind of solar cells. Therefore, triple junction InGaP/GaAs//Silicon tandem solar cells continue being very attractive for further development, using high efficiency HIT silicon cell as the bottom sub-cell.