Solar cells design as an independent supply for biosensor Field Effect Transistor (bioFET) is required to overcome electricity supply. Integrating bioFET with solar cells generates some benefits that include efficiency, low costs, and environmental friendly. In the design of solar cells, the bifacial structure of Hetero-junction Intrinsic Thin layer (HIT) was selected, and the optimization on the structure was carried out with the help of AFORS-HET software. The optimization of such a structure was undertaken by laying the intrinsic thin layers on both sides of the substrate or Transparent Conductive Oxides (TCO) that were placed on the front and back sides of the cell. In order to minimize the recombination, a back-surface field (BSF) was also put in the rear cell of the structure. Research on bifacial HIT structure needs to be done to select a solar cells structure that is most suitable with the voltage required by the bioFET. There are five structures modeling had done to have suitable structure using AFORS-HET. The entire five structures had been simulated on equilibrium mode, and they generally have shown to possess a band alignment type II, namely staggered heterojunction. The simulation results in equilibrium mode obtained one structure which the smallest ΔEC and ΔEV among the other four structures, that is TCO / a-Si:H(p) / a-Si:H(i) / c-Si(n) / a-Si:H(i) / a-Si:H(n+) / TCO / Al with ΔEC and ΔEV, 0.15006798 eV and 0.445920 eV respectively. This 2nd structure also has a smallest barrier in ΦBn= 0.6791392 eV and ΦBp= 0.08314 eV, respectively. The built-in potential of the 2nd structure is 1.13 V. This structure has JSC=0.083 A/cm2 and VOC = 0.313 V. The deviation between built-in potential and VOC is realize in 0.817. The maximum current and maximum voltage are Jm = 0,076 A/cm2 and Vm = 0,25 V respectively, so the maximum power of this structure is 0.019 Watt/cm2. Therefore the 2nd structure is the most appropriate structure to fulfill the bioFET supply.