Researchers at the University of Exeter in the United Kingdom has developed a novel type of smart window that integrates PV modules with polymer-dispersed liquid crystal (PDLC). PDLC is a smart film composed of liquid-crystal droplets in a polymer matrix that switches from opaque to transparent when an electric field is applied.

“Previous smart window systems attempted to integrate power generation using conventional PV or tandem structures; however, these approaches often faced performance and stability limitations,” said lead author Aritra Ghosh to pv magazine. “In contrast, the proposed structure operates effectively without such issues, demonstrating stable performance while maintaining the desired thermal and optical properties.”

Ghosh tested two configurations, each in on and off states. In one, the PDLC layer faces the sun first (PDLC–BIPV); in the other, the PV layer faces the sun first (BIPV–PDLC). “Both arrangements show very similar heat transfer coefficients (U-values) and solar heat gain coefficients (g-values),” he said. “The main difference occurs when the PV layer is on the exterior, which slightly alters overall performance.”

Both systems used glass and acrylic films measuring 0.3 m × 0.21 m × 0.004 m. The PV cells and PDLC films were sandwiched between glass and acrylic glazing, with either the cell or the film on top. The PDLC film becomes transparent under 20 V AC and translucent when unpowered. Six 0.43 W PV cells were installed inside the window in two parallel strings of three cells each.

“An indoor sun simulator provided continuous illumination at 1,000 W/m²,” Ghosh explained. “We measured temperatures of the PV cells, test cell, external and internal acrylic surfaces, and indoor ambient air using T-type thermocouples connected to a Picco data logger. The MP160 IV-tracer collected IV data using a 4-wire connection. Data were recorded every five minutes to minimize mismatch errors between the two acquisition systems.”

In the ON state (BIPV–PDLC ON and PDLC–BIPV ON), the system showed 62% solar transmission and 18% reflection, with a haze of 15%. The solar skin protection factor (SSPF) reached 78%, and the solar material protection factor (SMPF) was 43%. Visual performance remained high, with a correlated color temperature (CCT) of 5,983 K and a color rendering index (CRI) of 97. The solar heat gain coefficient was 0.54, and the thermal transmittance (U-value) was 5.2 W/m²K. Higher light transmission in the ON state also resulted in higher PV cell temperatures.

In the OFF state (BIPV–PDLC OFF and PDLC–BIPV OFF), solar transmission dropped to 42%, reflection to 17%, and haze increased to 71%. SSPF improved to 90% and SMPF to 71%. CCT fell to 5,273 K, CRI to 91, g-value to 0.43, and U-value to 4.7 W/m²K.

The results suggest that combining PDLC with integrated PV modules could offer a viable path for multifunctional building façades. By providing switchable transparency, effective solar protection, and electricity generation in a single window unit, the system could improve occupant comfort, reduce energy use, and enhance the sustainability of buildings.

The new system was presented in “Thermal-optical-electrical performance of combined photovoltaic-polymer dispersed liquid crystal for switchable BIPV-smart window,” published in the Journal of Building Engineering. Ghosh and his team say further work will explore larger-scale prototypes and long-term performance under real-world conditions.

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