Abstract In this effort, 10 μm thick rear contact (RC) silicon–germanium (SiGe) based solar cell device has been discussed with SiC (20 nm)-based front surface passivation for the suppression of interface recombination as well as improvement of short circuit current density ( J SC ) and open-circuit voltage ( V OC ). The design principles presented here balance the electronic and photonic effects together and is a significant step to design highly efficient thin solar cells. Photo reflectance is significantly reduced in the UV/visible spectral region due to the presence of SiC. This results in external quantum efficiency (EQE) >90% in the spectrum range of 400–650 nm wavelength. Also, at wavelengths equivalent to 300 nm, SiC passivated device shows record EQE of 85%. The presence of SiC as a surface passivating layer shows enhanced surface characteristics in terms of reduced surface recombination and higher photon absorption rate. This results in 15.4% power conversion efficiency (PCE) under standard air mass 1.5 illuminations. Further, the proposed device has also been analyzed for concentrator photovoltaics (CPV) applications, resulting in 18.4% and 19.3% efficiencies at 1 W/cm 2 (10 suns, 27 °C) and 2 W/cm 2 (20 suns, 27 °C) respectively. Till date, the proposed design proves to be highly efficient in the sub 10 μm regime. All the simulations have been done using DEVEDIT and ATLAS device simulator