Polymer Encapsulants Incorporating Light‐Guiding Architectures to Increase Optical Energy Conversion in Solar Cells

Abstract

The fabrication of a new type of solar cell encapsulation architecture comprising a periodic array of step-index waveguides is reported. The materials are fabricated through patterning with light in a photoreactive binary blend of crosslinking acrylate and urethane, wherein phase separation induces the spontaneous, directed formation of broadband, cylindrical waveguides. This microstructured material efficiently collects and transmits optical energy over a wide range of entry angles. Silicon solar cells comprising this encapsulation architecture show greater total external quantum efficiencies and enhanced wide-angle light capture and conversion. This is a rapid, straightforward, and scalable approach to process light-collecting structures, whereby significant increases in cell performance may be achieved.

Enhanced Wide‐Angle Energy Conversion Using Structure‐Tunable Waveguide Arrays as Encapsulation Materials for Silicon Solar Cells

“…One encapsulation structure that shows promise to increase optical energy capture consists of a periodic array of vertically aligned broadband optical waveguides . The structure can be produced by employing light‐induced self‐writing (LISW) of microscale cylindrical waveguides in a photocurable resin consisting of a high and low index polymer (relative to one another), whereby LISW couples to photopolymerization‐induced phase separation to form a core (high index polymer) and cladding (low index polymer) architecture of cylindrical symmetry that establishes the refractive index profile necessary to transmit light via waveguided modes .…”

Direct Light‐Writing of Nanoparticle‐Based Metallo‐Dielectric Optical Waveguide Arrays Over Silicon Solar Cells for Wide‐Angle Light Collecting Modules

“…The waveguide acceptance range (Δθ) is calculated based on the refractive index of the core ( n 1 ) and the surroundings (i.e., cladding) ( n 2 ) according to . Using the refractive index values of the polymers (NOA65: 1.653, PDMS:1.412),13a a maximum acceptance range of 30° is possible. It is above this value that light is observed to begin “leaking” out of the waveguide cores (contrast Figure e to h with m to p).…”

“…We hereon compare the solar cell performances of the metallo‐dielectric waveguides relative to waveguides with no silver nanoparticles (i.e., 0 wt%), which has been established to widen the acceptance range relative to a uniform encapsulant 13a . Figure shows EQE measurements of encapsulated solar cells for the range of AgSbF 6 concentrations explored.…”

“…We recently demonstrated the capability for polymer waveguide arrays to enhance nonnormally incident light collection . The waveguide arrays are produced in a photo‐reactive blend of high and low refractive index polymers irradiated with arrays of microscale optical beams.…”

“…Irradiation with an array of UV beams creates periodic waveguide array architectures with the waveguide cores consisting of a homogenous distribution of silver nanoparticles. Our strategy herein is to leverage the waveguide array to provide a baseline structure for a wider light acceptance window, which already performs better than a uniform encapsulant, and for the in situ synthesized nanoparticles to impart further optical functionality—through light scattering—thereby enhancing the collection of light (both normally and nonnormally incident) through a synergy between light‐guiding and light scattering. We systematically vary the AgSbF 6 content to produce waveguide cores with different silver nanoparticle concentrations, and investigate as a function of AgSbF 6 concentration performance enhancements specifically in terms of the EQE and current density.…”