Colour-neutral photovoltaic windows with performance linearly tuneable with transmittance

Abstract

Building-integrated photovoltaics (BIPV) are predicted to become a cornerstone in the energy transition by enabling on-site electricity generation. While rooftop and opaque façade integrations currently dominate, the widespread use of glass façades in modern architecture presents an untapped opportunity for energy harvesting. This potential remains unexploited due to the absence of suitable semi-transparent photovoltaic (STPV) technologies meeting all requirements, such as suitable average visual transmittance (AVT), spectral quality (expressed as colour rendering index – CRI), and visual comfort (e.g. undisturbed views). In this work, we demonstrate the superior optical and electrical performance of a new STPV concept based on interdigitated micro-stripes of chalcogenide solar cells and bare glass. We compare the micro-stripe geometry with ultra-thin absorber approaches both as energy generators and daylight-transmitting windows, evaluating performance across daily and seasonal cycles. Proof-of-concept micro-striped Cu(In,Ga)Se2 STPV devices with AVT ranging from 30 to 70% are demonstrated. Notably, we achieve a record power conversion efficiency of 2.5% at a high AVT of 64% and an excellent 5.8% efficiency at 34% AVT, both with a colour rendering index exceeding 99. These results position micro-striped Cu(In,Ga)Se2 STPV as a highly promising pathway towards power-generating windows.