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 (MgF 2 ) and a top MgF 2 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 MgF 2 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/cm 2, 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.