Design of Quadruple‐Layer Antireflection Coating for AlGaInP/AlGaAs/GaAs Three‐Junction Solar Cell

Abstract

A combination of AlGaInP/AlGaAs/GaAs is commonly used in world‐record five‐ and six‐junction solar cells for their easily tunable bandgap and nearly matched lattice constants. Wide‐range low reflectivity is of significant importance in this three‐junction solar cell (3JSC), but also difficult to achieve particularly in 300–400 nm due to the optical properties of III–V alloys. Therefore, quadruple‐layer antireflection coatings (QLAR) composed of ZnS and MgF2 films are studied in this article for both performance and practicability. Optical constants of ZnS and MgF2 films are extracted by variable angle spectroscopic ellipsometry. 150 °C is determined as the best deposition temperature to decrease parasitic absorption in ZnS films. The antireflection coating is designed by the transfer‐matrix method considering both low reflectivity in a wide range of 300–900 nm and balanced subcell current density. Fabricated 3JSC with optimized MgF2/ZnS/MgF2/ZnS QLAR is demonstrated to possess low reflection losses in a broadband spectral range, with an average of only 1.59% in 300–900 nm. This boosts the integral current density to 11.58, 11.35, and 11.25 mA cm−2 for AlGaInP, AlGaAs, and GaAs subcells, respectively.