The efficiency of perovskite solar cells (PSCs) has reached an astounding mark of 26.7% thanks to recent developments, particularly in those which utilize organic-inorganic Lead halides based perovskite light harvesting absorbers. However, Lead toxicity is still a foremost barrier towards their wider commercialization owing to the associated environmental issues. The present research delves at novel, environmental friendly PSCs those are based upon Lead free CsGeI3 and RbGeI3 perovskite absorbers. The proposed PSCs comprise device architecture as FTO/TiO2/CsGeI3/GO/Au and FTO/TiO2/RbGeI3/GO/Au those are numerically simulated by SCAPS-1D software. The parameters pertaining to the absorber layer, including its thickness, defect density and acceptor density, are optimized and the CsGeI3 based device achieves outstanding performance with Voc of 1.3960 V, FF of 79.13%, Jsc of 24.04 mA/cm2, PCE of 26.56%, at absorber layer’s optimized condition of thickness 1000 nm, acceptor density 2 × 1021 cm−3, defect density 1 × 1012 cm−3 and temperature 300 K. Whereas the RbGeI3 based device accomplishes Voc of 640.5 mV, FF of 78.38%, Jsc of 28.81 mA/cm2 and PCE of 14.46% where, the optimized conditions bear thickness 400 nm, acceptor density 1 × 1016 cm−3, defect density 1 × 1012 cm−3 and temperature 300 K. The present work intended to optimize Lead free Germanium based halide PSCs by using SCAPS-1D in order to lay the foundation for developing advanced Pb free, Ge based PSCs those could offer substantial potential for achievement of high conversion efficiencies and subsequent commercialization.