Influence of μc-Si:H tunnel recombination junction on the performance of a-Si:H/μc-Si:H tandem solar cell

Numerical simulations of hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) p-i-n type tandem solar cell with a μc-Si:H n-p type tunnel recombination junction (TRJ) between the a-Si:H top cell and the μc-Si:H bottom cell are carried out using the simulator Silvaco-Atlas. Photovoltaic characteristics of a-Si:H and μc-Si:H solar cells and a-Si:H/μc-Si:H tandem solar cell were simulated first and their efficiencies of about 10.22%, 6.5% and 12.69% respectively, agree well with experimental reported record efficiencies. Influence of parameters such as dopant concentrations and thickness of the TRJ on the tandem solar cell are then studied. The simulated results demonstrate that the short-circuit current, the open-circuit voltage, the fill factor and the efficiency of the tandem cell are improved by increasing the donor concentration of the TRJ. On the other hand, the acceptor concentration and the thickness of the TRJ reduce mainly the short-circuit current, the fill factor and the efficiency while the open-circuit voltage changes slightly. This study shows a strong recombination process occurred in the TRJ, the highest conversion efficiency of 12.73% is achieved when the peak of the recombination rate is approximately located in the middle of the TRJ p-layer where the quasi-Fermi levels are close to each other.