Investigations on Optical, Material and Electrical Properties of aSi:H and aSiGe:H in Making Proposed n+aSi:H/i-aSi:H/p+aSiGe:H Graded Bandgap Single-junction Solar Cell

Objective: This work identifies materials that satisfy refractive index, optical band gap, composition profile, conductivity, hall mobility, carrier type and carrier concentration to utilize them in making thin film photovoltaic cells. Methods: We fabricated phosphorous doped amorphous silicon (n+ aSi:H), boron doped amorphous silicon germanium(p+ aSiGe:H) and intrinsic amorphous silicon (i-aSi:H). A detailed and systematic characterization of the fabricated layers was done. The phosphorous doped amorphous silicon (n+ aSi:H) showed an optical band gap of 1.842 eV and an electron mobility of 295.45 cm²V^-1s^-1. The boron doped amorphous silicon germanium (p+ aSiGe:H) exhibited an optical band gap of 1.74 eV and a hole mobility of 158.353 cm²V^-1s^-1. The intrinsic amorphous silicon (i-aSi:H) has an optical band gap of 1.801 eV. The films of n+ aSi:H, i-aSi:H and p+ aSiGe:H can be utilized for fabricating graded band gap single junction thin film solar cells, as they are semiconducting materials with varying band gaps in the range of 1.74 eV to 1.84 eV. The tailoring of band gap achieved by the proposed material combination has been presented using its energy band diagram. Results: In this work, we are proposing a single junction graded band gap solar cell with aSi:H and aSi- Ge:H alloys of varying doping to achieve grading of band gap, which improves the efficiency while keeping the cell compact and light. Conclusion: As a first step in the validation, we have simulated a thin film solar cell using SCAPS1D simulation software with the measured parameters for each of the layers and found that it successfully performs as solar cell with an efficiency of 14.5%.