Application of polydimethylsiloxane surface texturing on III-V//Si tandem achieving more than 2 % absolute efficiency improvement

Silicon based multi-junction solar cells are a promising approach for achieving high power conversion efficiencies using relatively low-cost substrates. In recent years, 2-terminal triple-junction solar cells using GaInP/GaAs as top cells and Si bottom cell have achieved excellent efficiencies. Epitaxial growth or wafer bonding has been used for the integration of the cells. This requires the top surface of the Si cell to be polished for effective integration, sacrificing the light trapping in the Si cell. The poor long wavelength light absorption in silicon limits the tandem cell efficiency as it is limited by current mismatch. In this work, for the first time, an external surface texturing is attached onto a GaInP/GaAs//Si wafer bonded triple-junction solar cell, using polydimethylsiloxane (PDMS) layers with surface geometries replicated from various pyramidally-textured silicon wafers. With reduced reflection, the short circuit current density is increased by 0.95 mA/cm2, while the overall cell efficiency is boosted by more than 2 % absolute.