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Published February 24, 2020 | Supplemental Material
Journal Article Open

Autonomous Light Management in Flexible Photoelectrochromic Films Integrating High Performance Silicon Solar Microcells


Commercial smart window technologies for dynamic light and heat management in building and automotive environments traditionally rely on electrochromic (EC) materials powered by an external source. This design complicates building-scale installation requirements and substantially increases costs for applications in retrofit construction. Self-powered photoelectrochromic (PEC) windows are an intuitive alternative wherein a photovoltaic (PV) material is used to power the electrochromic device, which modulates the transmission of the incident solar flux. The PV component in this application must be sufficiently transparent and produce enough power to efficiently modulate the EC device transmission. Here, we propose Si solar microcells (μ-cells) that are i) small enough to be visually transparent to the eye, and ii) thin enough to enable flexible PEC devices. Visual transparency is achieved when Si μ-cells are arranged in high pitch (i.e. low-integration density) form factors while maintaining the advantages of a single-crystalline PV material (i.e., long lifetime and high performance). Additionally, the thin dimensions of these Si μ-cells enable fabrication on flexible substrates to realize these flexible PEC devices. The current work demonstrates this concept using WO₃ as the EC material and V₂O₅ as the ion storage layer, where each component is fabricated via sol-gel methods that afford improved prospects for scalability and tunability in comparison to thermal evaporation methods. The EC devices display fast switching times, as low as 8 seconds, with a modulation in transmission as high as 33%. Integration with two Si μ-cells in series (affording a 1.12 V output) demonstrates an integrated PEC module design with switching times of less than 3 minutes, and a modulation in transmission of 32% with an unprecedented EC:PV areal ratio.

Additional Information

© 2020 American Chemical Society. Received: October 8, 2019; Accepted: January 31, 2020; Published: January 31, 2020. The development of the materials chemistries and device form factors for autonomous electrochromic systems integrating high-performance microcell materials was carried out with support from the "Photonics at Thermodynamic Limits" Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0019140. This work exploits microcell PV materials developed with the support of the "Light-Material Interactions in Energy Conversion" Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001293 (subcontract no. 67N-1087758). The experiments used the facilities at the Materials Research Laboratory and Center for Microanalysis of Materials at the University of Illinois at Urbana-Champaign. Dynamic Mechanical Analysis (DMA) was performed by Leon Dean in the Sottos Research Group at the University of Illinois at Urbana Champaign, Department of Materials Science and Engineering. Author Contributions: M.M.P., M.A.Y.: These authors contributed equally to the work. The authors declare no competing financial interest.

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August 19, 2023
October 19, 2023