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

• Published in: ACS applied energy materials 2020-02, Vol.3 (2), p.1540-1551
• Main Authors: Potter, Maggie M, Yoder, Mikayla A, Petronico, Aaron, Lehman, Sean E, Nicolau, Bruno G, Enright, Michael J, Phelan, Megan, He, Junwen, Atwater, Harry A, Nuzzo, Ralph G
• Format: Article
• Language: English
• Subjects: electrochromic devices; microcells; optics, phonons, thermal conductivity, charge transport, materials and chemistry by design, mesostructured materials, synthesis (novel materials); photoelectrochromic windows; photovoltaics; smart windows
• ISSN: 2574-0962; 2574-0962
• DOI: 10.1021/acsaem.9b01987

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 EC 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 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 s, 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 min and a modulation in transmission of 32% with an unprecedented EC:PV areal ratio.