Colored solar cells with spectrally selective photonic crystal reflectors for application in building integrated photovoltaics

Abstract

In this article, we have reported a nanophotonic coating called Selectively Modulated Aesthetic Reflector Technology (SMART), which can be integrated to any matured solar cell technology to produce colored solar cells or modules. This technology has a potential significance in building integrated photovoltaics to improve aesthetics along with being commercially feasible. As a proof of concept, we have integrated this technology into crystalline silicon solar cells. Here we have used one-dimensional dielectric photonic crystals to selectively reflect the light, to realize multi-color appearances for the solar cells. Silicon Nitride (SiN) and Silicon Oxynitride (SiON) dielectric layers with varying compositions and thickness were used to fabricate these SMART coatings. The optoelectronic effects have been elucidated by spectroscopic, quantum efficiency and I-V measurements. The color perception has been quantitatively investigated using CIE (International Commission on Illumination) 1931 chromaticity diagram. The CIE color co-ordinates for the SMART coatings were (0.39, 0.32), (0.25, 0.38) and (0.20, 0.17) respectively for Red, Green and Blue (RGB) colours and (0.27, 0.29) for white. The cells show an integrated transmittance between 60 and 80% in the absorption regime of the solar cell depending on its color. The efficiency and the performance of different colored solar cells namely RGB and white have been shown on 156 cm2 cell area. The RGB colors have a relative power conversion efficiency of ∼70–80% based on different colors whereas white has a relative efficiency of 59% as compared to the standard reference silicon solar cell. This process is industrially feasible and could utilize the vertical area of buildings, which could have a significant application in urban landscaping.