Arbitrary and active colouring of solar cells with negligible loss of efficiency

While the current surging global energy crisis highlights the urgent need for a transition to renewable energy sources, the large physical footprint—as experienced by humans—of the required installations reduces public acceptance and therefore strongly hampers its development. Solar modules, for electricity and/or for heating, do not have the audible impact of wind turbines but their visible impact is currently prohibitive for many installation options, such as on the façades of buildings. Here we show that coatings of cholesteric liquid crystals (CLCs) can turn any black solar modules into passive surfaces with arbitrary colour or active surfaces with temperature sensitive colouration, yet with minimum loss of power conversion efficiency (PCE), thanks to their self-organized helical modulation generating structural colour. Most conspicuously, we combine red, green, and blue pixels to generate a non-spectral colour that blends into wooden or metallic backgrounds with a 50% relatively higher PCE than a ceramic ink equivalent since CLCs neither absorb nor scatter light. Further, we show thermochromic solar cells with colour tunable across the full visible spectrum, maintaining 88% of their original PCE. We argue these coatings can be developed to cover solar modules with either arbitrary full-colour images, allowing them to be aesthetically integrated into building façades and roofs in a way that is fully acceptable by the public, or with active colour changing to add functional value, while always keeping high PCE.