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Silicon is the predominant semiconductor in photovoltaics. However, the conversion efficiency of silicon single junction solar cells is intrinsically constrained to 29.4%, and practically limited around 27%. It is nonetheless possible to overcome this limit by combining silicon with high bandgap materials, such as III-V semiconductors, in a multi-junction device. Despite numerous studies tackling III-V/Si integration, the significant challenges associated with this material combination has hindered the development of highly efficient III-V/Si solar cells. Here we demonstrate for the first time a III-V/Si cell reaching similar performances than standard III-V/Ge triple-junctions solar cells. This device is fabricated using wafer bonding to permanently join a GaInP/GaAs top cell with a silicon bottom cell.The key issues of III-V/Si interface recombination and silicon weak absorption are addressed using polysilicon/SiOx passivating contacts and a novel rear side diffraction grating for the silicon bottom cell. With these combined features, we demonstrate a 2-terminal GaInP/GaAs//Si solar cell reaching a 1sun AM1.5g conversion efficiency of 33.3%.

In order to utilize the full potential of solar cells fabricated on n-type silicon, it is necessary to achieve an excellent passivation on B-doped emitters. Experimental studies on test structures and theoretical considerations have shown that a negatively charged dielectric layer would be ideally suited for this purpose. Thus, in this work the negative-charge dielectric Al2O3 was applied as surface passivation layer on high-efficiency n-type silicon solar cells. With this front surface passivation layer, a confirmed conversion efficiency of 23.2% was achieved. For the open-circuit voltage Voc of 703.6mV, the upper limit for the emitter saturation current density J0e, including the metalized area, has been evaluated to be 29fA∕cm2. This clearly shows that an excellent passivation of highly doped p-type c-Si can be obtained at the device level by applying Al2O3.

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