Self-cleaning antireflective coating with a hierarchical texture for light trapping in micromorph solar cells
Surface texture plays a particularly important role in surface behaviors. Herein, we report a novel hierarchical texture combining microcone arrays with nanopits for minimizing the reflection loss at the air/glass interface. Its optical properties were confirmed via spectral characterization (reflectance, transmittance and haze) and FDTD numerical simulation. The results reveal that nanopits provide a gradient index profile for improving index discontinuity and are advantageously antireflective in a shorter wavelength while microcone arrays allow multi-reflection for light scattering and prevail over a longer wavelength region. The hierarchical texture resulting from the combination of both exhibits dramatic broadband light trapping over the entire visible spectrum. Moreover, without fluorosilane modification, the hierarchical texture allows a superhydrophobic surface (contact angle of ca. 136°) due to its higher roughness. The light trapping performance of the hierarchical texture onto the front glass surface of the micromorph cell was investigated by photoelectrical current–voltage curves and external quantum efficiency spectra. The results indicate that both the number of trapped photons and their optical path length in the absorbed layer are increased, thereby achieving an overall efficiency of 11.44% out of the bare device of 10.93% efficiency, resulting in a 4.7% enhancement. Additionally, the proposed method paves a promising way for light trapping in other solar applications, owing to its advantages of large area, low cost and facile fabrication.