Researchers from Kyung Hee University and Hyundai Motor Group have developed an AI-based inverse design strategy that enables full-color, high-efficiency semitransparent perovskite solar cells for applications such as solar windows and vehicle glazing. The work introduces a modelling-guided framework that integrates all-dielectric multilayer coatings - composed of alternating zinc sulfide (ZnS) and magnesium fluoride (MgF₂) - into perovskite photovoltaics, allowing user-defined transmitted colors with minimal optical loss.
Photographs of semitransparent PVSK PVs. Left: uncoated Right: ZnS/MgF2-coated. Image from: Opto-Electronic Advances
Unlike conventional color-tuning methods that rely on metallic or absorptive films, the team’s approach employs transparent interference coatings designed through a digital optimization loop. Each layer sequence is encoded as a binary string and evaluated by a factorization machine-based surrogate model trained on optical simulations. The optimization, expressed as a quadratic unconstrained binary optimization (QUBO) problem, identifies the precise ZnS/MgF₂ configurations that meet specific color coordinates and average visible transmittance (AVT) targets.
The system produced six target hues - red, green, blue, cyan, magenta, and yellow - across perovskite absorber thicknesses between 65 nm and 165 nm. A representative cyan device with a 110 nm-thick MAPbI₃ absorber achieved a peak transmittance of 10.4% and AVT = 6.5% on glass, corresponding to a 20.9% increase in power conversion efficiency (PCE) compared to the uncoated device. On flexible PET substrates, the same coating reached a peak transmittance of 14.6%, AVT = 5.3%, and a 10.4% PCE gain, while maintaining mechanical flexibility and optical clarity.
All coatings were deposited by thermal evaporation directly on operational solar cells, confirming integration compatibility with commercial manufacturing. To enhance process versatility, the researchers also demonstrated a lamination-based assembly, where ZnS/MgF₂ stacks were pre-coated on PET films before attachment - avoiding potential damage from thermal or plasma exposure.
Because the framework depends solely on measured optical constants instead of empirical tuning, it can be easily adapted to other thin-film PV systems such as organic, CIGS, or tandem devices. Further refinements, including higher-bit digital encoding (50–100 bits via simulated annealing or quantum annealing), are expected to yield enhanced color purity and broader chromaticity control.
This work addresses the long-standing trade-off between aesthetics and performance in transparent photovoltaics. By transforming reddish-brown-tinted semitransparent perovskites into bright, user-selectable colors without sacrificing efficiency, the researchers have opened a pathway toward architectural and automotive solar integration - turning windows, façades, and even wearable devices into power-generating surfaces that complement their surroundings.
