High quality optical and optoelectronic materials for efficient light management and solar spectrum control and conversion

Optoelectronic devices that effectively manipulate and manage light are of great interest in multiple fields, particularly in photovoltaics (PV) as a way to absorb and convert light into electricity. On the other hand, display technologies exploit optical materials and optoelectronics to efficiently extract light from an emissive component. Regardless of industry, similar principles guide the research of these devices and can be utilized to improve upon existing designs or generate new, unique designs. This dissertation focuses on high performance optoelectronic devices for both PV and emissive display applications that employ similar principles to optimize optical pathways within the respective device design. We first explore ultrathin semiconductor designs that reduce costs of expensive materials and processing. Silicon solar microcells are re-designed to account for high series resistance and poor absorption. A back contact design significantly reduces the series resistance within the solar microcell and allows for an anti-reflection coating on the front surface to drastically improve the absorption of incident irradiation. Strategies for an improved concentration design are then explored that implement traditional lenses for concentration of direct light at high concentration ratios. Collection of diffuse light is then achieved through a luminescent solar concentrator (LSC) in the backplane of the lens array, contributing to additional achievable power on both clear and cloudy days. The improved solar microcells are then integrated with a low power density application, a self-powered electrochromic, or “smart” window. Here, the microcells are shown as an exemplar high performance and relatively transparent PV material to power such a window. Processes for fabrication of the self-powered electrochromic window are considered for scalability and ease of integration into industrial applications. These include sol-gel methods for preparation of active, electrochromic films and the ability to do processing on flexible substrates. The latter enables transitory capabilities as well as the possibility to include an adhesive for active retrofitting to existing windows. An electrochromic film powered by the Si microcells is demonstrated with transmission modulation on the order of 46%. Finally, we show a design for an emissive cavity to replace absorptive color filters in a liquid crystal display (LCD). Strategies from LSCs are exploited to design the emissive component, quantum dots embedded in a polymer waveguide. The quantum dots used here have high quantum yields and narrow bandwidths, which are necessary if an RGB display is to be realized. Additionally, the Stokes shift of the quantum dots is large, which reduces reabsorption events within the polymer waveguide. The waveguide is then integrated into a reflective cavity that reflects luminesced photons (especially those emitted from the edge of the waveguide) towards a small top aperture. High extraction efficiencies are achieved with this design and a micropixel array is presented as a prototype for integration into an LCD panel

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

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

High quality optical and optoelectronic materials for efficient light management and solar spectrum control and conversion

Optoelectronic devices that effectively manipulate and manage light are of great interest in multiple fields, particularly in photovoltaics (PV) as a way to absorb and convert light into electricity. On the other hand, display technologies exploit optical materials and optoelectronics to efficiently extract light from an emissive component. Regardless of industry, similar principles guide the research of these devices and can be utilized to improve upon existing designs or generate new, unique designs. This dissertation focuses on high performance optoelectronic devices for both PV and emissive display applications that employ similar principles to optimize optical pathways within the respective device design. We first explore ultrathin semiconductor designs that reduce costs of expensive materials and processing. Silicon solar microcells are re-designed to account for high series resistance and poor absorption. A back contact design significantly reduces the series resistance within the solar microcell and allows for an anti-reflection coating on the front surface to drastically improve the absorption of incident irradiation. Strategies for an improved concentration design are then explored that implement traditional lenses for concentration of direct light at high concentration ratios. Collection of diffuse light is then achieved through a luminescent solar concentrator (LSC) in the backplane of the lens array, contributing to additional achievable power on both clear and cloudy days. The improved solar microcells are then integrated with a low power density application, a self-powered electrochromic, or “smart” window. Here, the microcells are shown as an exemplar high performance and relatively transparent PV material to power such a window. Processes for fabrication of the self-powered electrochromic window are considered for scalability and ease of integration into industrial applications. These include sol-gel methods for preparation of active, electrochromic films and the ability to do processing on flexible substrates. The latter enables transitory capabilities as well as the possibility to include an adhesive for active retrofitting to existing windows. An electrochromic film powered by the Si microcells is demonstrated with transmission modulation on the order of 46%. Finally, we show a design for an emissive cavity to replace absorptive color filters in a liquid crystal display (LCD). Strategies from LSCs are exploited to design the emissive component, quantum dots embedded in a polymer waveguide. The quantum dots used here have high quantum yields and narrow bandwidths, which are necessary if an RGB display is to be realized. Additionally, the Stokes shift of the quantum dots is large, which reduces reabsorption events within the polymer waveguide. The waveguide is then integrated into a reflective cavity that reflects luminesced photons (especially those emitted from the edge of the waveguide) towards a small top aperture. High extraction efficiencies are achieved with this design and a micropixel array is presented as a prototype for integration into an LCD panel.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste