Fluorescent Waveguide Lattices for Enhanced Light Harvesting and Solar Cell Performance

Abstract

We present the properties and performance of fluorescent waveguide lattices as coatings for solar cells, designed to address the significant mismatch between the solar cell’s spectral response range and the solar spectrum. Using arrays of microscale visible light optical beams transmitted through photoreactive polymer resins comprising acrylate and silicone monomers and fluorescein o,o′-dimethacrylate comonomer, we photopolymerize well-structured films with single and multiple waveguide lattices. The materials exhibited bright green-yellow fluorescence emission through down-conversion of blue-UV excitation and light redirection from the dye emission and waveguide lattice structure. This enables the films to collect a broader spectrum of light, spanning UV–vis–NIR over an exceptionally wide angular range of ±70°. When employed as encapsulant coatings on commercial silicon solar cells, the polymer waveguide lattices exhibited significant enhancements in solar cell current density. Below 400 nm, the primary mode of enhancement is through down-conversion and light redirection from the dye emission and collection by the waveguides. Above 400 nm, the primary modes of enhancement were a combination of down-conversion, wide-angle light collection, and light redirection from the dye emission and collection by the waveguides. Waveguide lattices with higher dye concentrations produced more well-defined structures better suited for current generation in encapsulated solar cells. Under standard AM 1.5 G irradiation, we observed nominal average current density increases of 0.7 and 1.87 mA/cm2 for single waveguide lattices and two intersecting lattices, respectively, across the full ±70° range and reveal optimal dye concentrations and suitable lattice structures for solar cell performance. Our findings demonstrate the significant potential of incorporating down-converting fluorescent dyes in polymer waveguide lattices for improving the current spectral and angular response of solar cell technologies toward increasing clean energy in the energy grid.

Interplay of Luminophores and Photoinitiators During Synthesis of Bulk and Patterned Luminescent Photopolymer Blends

“…Recently, active luminescent WELs, herein referred to as LWELs, have also been demonstrated based on a binary photopolymer blend of the acrylate-based commercially available Norland Optical Adhesive 65 (NOA 65) and an epoxide-terminated polydimethylsiloxane (PDMS) oligomer. 29 Camphorquinone (CQ) was used as the free-radical photoinitiator, together with (4octyloxyphenyl)phenyliodium hexafluoroantimonate (OPPI) as co-initiator, to drive the epoxide end-group photopolymerization of PDMS. The luminophore fluorescein o,o′-dimethacrylate was also included in the blend (assumed to graft to NOA 65), which enables spectral conversion of incident UV-blue light to green photoluminescence in the final material.…”

“…30 In the LWEL system, the addition of fluorescein increases this refractive index contrast, likely due to increased phase separation or a greater refractive index across the sample, especially along the waveguide channels. 29 This is perhaps unsurprising since it is well-known that absorption spectrum overlap between the photosensitizer and embedded luminophore (as is the case for CQ and fluorescein) affects both the cure depth and degree of photopolymerization. 18,31 For example, detailed studies by Lalevée and co-workers demonstrated that fluorescent dyes from the naphthalimide family could influence the photoinitiation of methacrylates, acrylates and their blends systems, using both free-radical and cationic polymerization mechanisms, which affected both the integrity and mechanical properties of 3D-printed structures; however, the fluorescence properties were not investigated in detail.…”

Interplay of Luminophores and Photoinitiators during Synthesis of Bulk and Patterned Luminescent Photopolymer Blends

“…Recently, active luminescent WELs, herein referred to as LWELs, have also been demonstrated based on a binary photopolymer blend of the acrylate-based commercially available Norland Optical Adhesive 65 (NOA 65) and an epoxide-terminated polydimethylsiloxane (PDMS) oligomer. 29 Camphorquinone (CQ) was used as the free-radical photoinitiator, together with (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate (OPPI) as co-initiator, to drive the epoxide end-group photopolymerization of PDMS. The luminophore fluorescein o,o′-dimethacrylate was also included in the blend (assumed to graft to NOA 65), which enables spectral conversion of incident UV-blue light to green photoluminescence in the final material.…”

“… 30 In the LWEL system, the addition of fluorescein increases this refractive index contrast, likely due to increased phase separation or a greater refractive index across the sample, especially along the waveguide channels. 29 This is perhaps unsurprising since it is well known that absorbance spectrum overlap between the photosensitizer and embedded luminophore (as is the case for CQ and fluorescein) affects both the cure depth and degree of photopolymerization. 18 , 31 For example, detailed studies by Lalevée and co-workers demonstrated that fluorescent dyes from the naphthalimide family could influence the photoinitiation of methacrylates, acrylates, and their blend systems using both free-radical and cationic polymerization mechanisms.…”