Broadband Angular Color Stability Of Dielectric Thin Film-Coated Pyramidal Textured Si For Photovoltaics

In this work we demonstrate the angular color stability of textured c-Si substrates colored by single layer thin film coatings ofSiN x. These coatings show higher angular color stability on substrates with a random upright pyramidal surface texture compared to identical coatings on planar silicon substrates. Angle dependent reflectance measurements, supported by a modeling framework, display that the reflectance peaks originating from thin film interference of coated textured substrates only shift about 15nm with an increasing angle of incidence from10 degrees to80 degrees, while the reflectance peaks of planar substrates with identical coatings shift about 120nm at these angles. More specifically, reflectance peaks of planar substrates shift to shorter wavelengths, leading to a blue shift of the color appearance. The stable peak position of the textured samples is explained by a 2D representation of their surface texture and the primarily double interference interaction on it. While it is well known that a wide range of colors can be realized exhibiting low optical losses with thin film coatings, angular color stability was often not taken into account. However, for building integrated photovoltaics applications, a high angular color stability is desired, underlining the importance of using these textures. In most installed c-Si photovoltaics, similar substrate surface textures and dielectric thin film layers are already used. Therefore, this work envisions a route to facilitate large scale production of colored solar cells on textured c-Si substrates, colored by thin filmSiN x layers, with minimized optical losses and improved angular color stability.