a-Si/a-Si tandem cells have a higher fill factor (FF), and lower light degradation than the single junction due to an intrinsic high electric field. Also, they are thinner and cheaper than a-Si single junction solar cells. This paper presents experiment results of a-Si/a-Si tandem solar cells deposited by a High-Density Plasma Chemical Vapor Deposition (HDPCVD) and uses AMPS-1D to simulate the performance of different material compositions at the recombination junction (RJ), including n-a-Si/p-a-Si, n-a-Si/p-mc-Si, n-mc-Si/p-mc-Si, and n-mc-Si/p-a-SiC.[2,4] In the experiment, although we found that as the thickness of the n-a-Si and p-a-Si layers of the RJ decreased, and the flow rate of PH
for the n-a-Si layer of the top cell lowered, the photocurrent (Jsc) and FF increased due to a reduced barrier height at the n-layer that facilitates the recombination and tunneling. The simulation results showed that the n-mc-Si/p-mc-Si composition had the best performance at the tunneling junction, and its highest efficiency could reach 10.4%.