Broadband angular color stability of dielectric thin film-coated pyramidal textured Si for photovoltaics

Abstract

In this work we demonstrate the angular colour stability of textured c-Si substrates coloured by single layer thin film coatings of SiN x . These coatings show higher angular colour 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 15 nm with an increasing angle of incidence from 10 to 80 • , while the reflectance peaks of planar substrates with identical coatings shift about 120 nm at these angles. More specifically, reflectance peaks of planar substrates shift to shorter wavelengths, leading to a blue shift of the colour 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 colours can be realized exhibiting low optical losses with thin film coatings, angular colour stability was often not taken into account. However, for building integrated photovoltaics applications, a high angular colour 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 coloured solar cells on textured c-Si substrates, coloured by thin film SiN x layers, with minimized optical losses and improved angular colour stability.

Characterization of Luminescent Down-Shifting Spectral Conversion Effects on Silicon Solar Cells with Various Combinations of Eu-Doped Phosphors

“…Considerable effort has gone into developing methods by which to increase the conversion efficiency of C-Si solar cells, including the formation of pyramidal surface structures and the application of anti-reflective coatings [8][9][10][11][12]. Nonetheless, the conversion efficiency of C-Si solar cells at shorter wavelengths (UV-blue band) remains low due to three key issues: (1) lower responsivity of C-Si in the UV-blue wavelength range; (2) loss of higher energy incident photons within a short distance of the surface due to photo-carrier recombination caused by surface defects; (3) energy loss via thermalization when high energy photons generate carriers with excessive energy [13][14][15].…”