Optical Engineering of a Gradient Antireflective Coating to Boost the Current Density in Efficient Perovskite Solar Cells

Antireflection coatings (ARCs) are a well-established yet often underutilized strategy for enhancing light management in perovskite solar cells. In this study, we report on a scalable and effective ARC solution based on engineering a bilayer architecture composed of a planar magnesium fluoride (MgF2) and a top MgF2 layer deposited at tilted angles using low-energy vapor deposition. The tilted deposition induces a gradient in the refractive index between the two layers, enabling superior optical impedance matching at the air/device interface. Optical constants of both planar and tilted MgF2 layers were extracted via spectroscopic ellipsometry and incorporated into optical simulations to optimize the layer thicknesses. Excellent agreement between modeling and experimental data was achieved (error <1%). The optimized device reaches a power conversion efficiency of 23.7%, with open-circuit voltage Voc = 1.137 V, Jsc = 24.7 mA/cm2, and a fill factor of 84.3%. Structural and morphological analyses confirm the presence of nanostructures promoting light trapping, while contact angle measurements indicate enhanced hydrophobicity and antisoiling behavior.