Researchers at University College London have developed semi-transparent solar windows. The windows generate electricity from both daylight and indoor lighting. The work appears in the journal Advanced Energy Materials. It raises a practical question for architects and building owners: could glass become a power source?
The research team is international, led from UCL. Dr Mojtaba Abdi-Jalebi of UCL said the motivation was to make better use of one of the largest untapped surfaces in modern architecture: glass. Rooftops already carry solar panels across many cities. The vast window areas of office blocks and homes remain largely unused as an energy resource.
How the Windows Work
The cells use perovskite, a class of light-absorbing crystal material that has attracted significant research interest over the past decade. The perovskite absorber layer is just 185 nanometres thick. That is far thinner than conventional perovskite layers. The team tuned it to capture indoor light with particular efficiency. Computer modelling shaped the layer structure from the outset.
The prototype admits around 30 per cent of sunlight. Ordinary glass typically admits 80 to 90 per cent. The partial tinting is an engineering trade-off between transparency and energy yield.
The electrode design presented its own challenge. The team used a thin sheet of gold placed between two layers of molybdenum oxide. This configuration conducts electricity while allowing light through. A conventional metal layer would have blocked too much light.
The researchers also added a molecule called 3-trifluoromethyl-1H-1,2,4-triazole to the cell structure. It reduces electronic defects and improves the stability of the crystal lattice.
Performance in Testing
The team tested a panel measuring 30 centimetres by 30 centimetres. Under bright indoor lighting, the device converted 22 per cent of incoming light into electricity. Under direct sunlight, it converted 14 per cent. The bare device retained 80 per cent of its efficiency after 300 hours in a standard accelerated durability test.
Lead author Siming Huang said the partial tinting effect could also reduce cooling demand. It cuts the amount of heat entering a building. That makes the technology particularly relevant in hotter regions. In those climates, air conditioning accounts for a large share of electricity consumption.
The 14 per cent outdoor conversion efficiency is below that of commercial silicon solar panels, which typically operate between 20 and 23 per cent. The indoor figure of 22 per cent is, however, competitive for ambient-light applications. The technology is at laboratory scale. The 300-hour durability test is shorter than the multi-decade performance guarantees required for commercial deployment.
A Growing Field
UCL’s work sits within a fast-moving area of solar research. Other studies have shown that semi-transparent perovskite cells can be tuned to trade off visibility and energy output. Researchers have also explored mixed self-assembled monolayer interfaces, ambient-air fabrication methods, and flexible substrate configurations. Interest in transparent photovoltaics has grown steadily across both academic and commercial settings.
The building-integrated photovoltaics market is still developing. Perovskite cells face well-documented questions around long-term stability and the presence of lead in many formulations. Regulatory and commercial hurdles remain substantial. The UCL team has shown one viable configuration, though the path from laboratory to building façade involves many further steps.
What Comes Next
The researchers say their longer-term ambition is to develop flexible solar films. These could go onto curved glass, vehicles, sunroofs, and other transparent surfaces. That would extend energy-generating architecture well beyond conventional window panes. No commercial timeline has been stated.
For investors and policymakers watching the energy transition, the UCL result is a data point worth tracking. Buildings account for around 40 per cent of global energy use, according to the International Energy Agency. Technologies that generate power from existing building surfaces could reduce demand on the grid without requiring new land. Glass-integrated solar is one candidate in that category.
The research was published in Advanced Energy Materials. The work was led by UCL in collaboration with an international team. Full details of the study, including methodology and materials characterisation, are available in the published paper.
