All-perovskite tandem solar cell is a new pathway to reach cost-effective yet highly efficient solar cells. In this work, we present vacuum-assisted growth control (VAGC) as a potential method to grow low-bandgap (LBG) FAxMA(1-x)Pb0.5Sn0.5I3 perovskite thin-films with enhanced charge-carrier lifetime compared to the well-established antisolvent method. The mixture of Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), and -Butyrolactone was optimized as perovskite solvents. LBG perovskite solar cells (PSCs) fabricated by the VAGC method exhibit PCE and stable PCE (SPCE) of 18.2% and 17.1%, respectively. Eventually, the LBG PSCs (EG ~ 1.27 eV) are mechanically stacked with semi-transparent wide-bandgap (WBG) PSCs (EG ~ 1.63 eV) and all-perovskite tandem solar cells with 23% PCE and 21.8% SPCE under one sun illumination are attainable.