Reflective Cavity Light Trapping for Thin-Film Photovoltaics
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Solution Overview
Problem
Thin-film photovoltaic devices face challenges with low photoabsorption efficiency due to their thin nature, leading to reduced external quantum efficiency and increased susceptibility to defects, while traditional light trapping methods using metal mirrors result in significant photon loss.
Innovation Solution
The implementation of a photovoltaic device structure that traps and recycles admitted light through a reflective cavity or waveguide, utilizing non-metallic Spectralon reflectors and optical concentrators to enhance light absorption without increasing bulk resistance, allowing for thinner photoactive layers and improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If thin-film photovoltaic devices are used, then device complexity and manufacturing cost are reduced, but photoabsorption efficiency decreases
Solution Approach 1:
The patent introduces a reflective cavity structure beneath the thin photoactive layer, transforming the light absorption problem from a two-dimensional surface interaction to a three-dimensional optical path extension. Light is reflected multiple times between the top and bottom reflective surfaces, increasing the effective optical path length without increasing the physical thickness of the device.
Solution Approach 2:
The patent introduces a waveguide mode as an intermediary mechanism to couple incident light into the thin photoactive layer. The waveguide mode acts as a mediator that enhances light confinement and interaction with the thin layer, enabling efficient coupling between free-space light and the thin photoactive material.
2Loss of energy
If traditional metal mirrors are used for light trapping, then light reflection is achieved, but photon loss increases due to absorption
Solution Approach 1:
The patent changes the material parameter of the reflective surfaces from metallic (high absorption) to dielectric or highly reflective metallic coatings (low absorption). By modifying the optical parameters of the reflective surfaces, the system achieves high reflectivity across broad spectral ranges while minimizing photon absorption losses.
Solution Approach 2:
The patent employs composite reflective structures combining multiple layers with different optical properties. The bottom reflective surface may combine metallic layers with dielectric overcoats to achieve both high reflectivity and broad spectral coverage, while the top reflective surface uses engineered dielectric stacks to minimize absorption losses.
3Reliability
If thicker photoactive layers are used, then light absorption increases, but bulk resistance and defect susceptibility increase
Solution Approach 1:
The patent resolves this contradiction by extending the optical path in the vertical dimension through multiple reflections in the cavity, rather than increasing the horizontal thickness of the photoactive layer. This allows sufficient light absorption to occur within a thin layer while avoiding the penalties of increased bulk resistance and defect density associated with thicker layers.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach increases light trapping and absorption efficiency, reducing losses across a large spectral range and enabling the use of thinner, more cost-effective photoactive layers with reduced defect susceptibility, thereby enhancing the overall performance of thin-film photovoltaic devices.
Implementation Method 1
The top layer comprises a transparent insulating layer, such as, for example, a spectralon reflector
Implementation Method 2
The present disclosure also relates to a low cost fabrication process for making such photovoltaic devices
Implementation Method 3
Photosensitive optoelectronic devices convert electromagnetic radiation into electricity
Data Source
AI summary
There is disclosed photovoltaic device structures which trap admitted light and recycle it through the contained photosensitive materials to maximize photoabsorption. For example, there is disclosed a photosensitive optoelectronic device comprising: a first reflective layer comprising a thermoplastic resin; a second reflective layer substantially parallel to the first reflective layer; a first transparent electrode layer on at least one of the first and second reflective layer; and a photosensitive region adjacent to the first electrode, wherein the first transparent electrode layer is substantially parallel to the first reflective layer and adjacent to the photosensitive region, and wherein the device has an exterior face transverse to the planes of the reflective layers where the exterior face has an aperture for admission of incident radiation to the interior of the device.