Color control in Cu(In,Ga)Se2 (CIGSe) solar cells for BIPV via the lift-off method and light interference transparent conductive oxide layers fabrication

Abstract

For Building-Integrated Photovoltaics (BIPV), the ability to produce a variety of colors is essential for architectural harmony. However, Cu(In,Ga)Se 2 (CIGSe) solar cells naturally have a rough growth surface that scatters light, significantly reducing the saturation and purity of interference-based colors. In this study, we demonstrate a color-control strategy that combines the mechanical lift-off method with light-interference bilayers transparent conductive oxide (TCO) ITO/IZO fabrication. The lift-off process was used to achieve a smooth interface on the CIGSe absorber bottom, reducing surface roughness (Ra) from 74.3 nm to 2.6 nm. The high planarization reduced diffuse reflection and allowed for precise thin-film interference, resulting in green, blue, and yellow colors that closely match with optical simulations on the CIE 1931 chromaticity diagram. To evaluate the impact of these aesthetic modifications on photovoltaic performance, full solar cells were fabricated. Conventional glass-substrate cells maintained power conversion efficiencies of 6.8–8.83% after coloring, while the high-saturation lift-off devices exhibited a significant performance decline, with efficiencies ranging from 2.07% to 3.78%. This efficiency drop was primarily driven by a decrease in short-circuit current density (Jsc) due to reduced light trapping on the smooth surface and increased reflectance at the targeted color peaks. Furthermore, the absence of the MoSe 2 interface layer and defects induced by the lift-off process contributed to a lower fill factor (FF). Consequently, while the lift-off method enables color variety through enhanced optical interference, it involves a trade-off between aesthetic quality and light absorption.