Antireflection Coating Design for Triple-Junction III-V/Ge High-Efficiency Solar Cells Using Low Absorption PECVD Silicon Nitride

The design of antireflection coating (ARC) for multi-junction solar cells is challenging due to the broadband absorption and the need for current matching of each subcell. Silicon nitride, which is deposited by plasma-enhanced chemical vapor deposition (PECVD) using standard conditions, is widely used in the silicon wafer solar cell industry but typically suffers from absorption in the short-wavelength range. We propose the use of silicon nitride deposited by low-frequency PECVD (LFSiN) optimized for high refractive index and low optical absorption as a part of the ARC design for III-V/Ge triple-junction solar cells. This material can also act as a passivation/encapsulation coating. Simulations show that the SiO2/LFSiN double-layer ARC can be very effective in reducing the reflection losses over the wavelength range of the limiting subcell for top subcell-limited, as well as middle subcell-limited, triple-junction solar cells. We also demonstrate that the structure's performance is stable over expected variations in the layer parameters (thickness and refractive index) in the vicinity of the optimal values.