Optically-Thin III-V Solar Cells With Lateral Light Trapping
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Solution Overview
Problem
Conventional quantum well and quantum dot solar cells face challenges in maximizing photon absorption and minimizing dark current, leading to lower photovoltaic power conversion efficiency due to limited light path length and high dark currents.
Innovation Solution
A solar cell structure is designed with a semiconductor junction depletion region extending into a base layer, incorporating a narrow band gap quantum well structure and a wider energy gap extended emitter, along with optional quantum dots, to enhance photon absorption and reduce dark current through advanced light trapping mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the cell thickness is decreased to reduce material costs and dark current, then dark current decreases and open circuit voltage increases, but absorption completeness decreases and short circuit current decreases
Solution Approach 1:
The patent transitions from vertical light propagation to lateral waveguide mode propagation by utilizing total internal reflection at the semiconductor-dielectric interface. This dimensional change in light path allows photons to travel laterally through the quantum well layer rather than vertically through the entire cell thickness, dramatically increasing the effective optical path length and absorption probability in thin-film structures.
Solution Approach 2:
The patent embeds narrow bandgap quantum well layers within a wider bandgap semiconductor matrix, creating a nested structure where the quantum wells are confined within the broader semiconductor layer. This nested configuration allows the quantum wells to act as optical traps for photons while the surrounding wider bandgap material provides structural support and electrical functionality.
2Adaptability or versatility
If quantum well structures are embedded to harness wide spectrum photons at high voltages, then spectral response improves, but light path length remains limited and absorption is hindered
Solution Approach 1:
The patent utilizes waveguide modes to redirect light propagation from the vertical dimension to the lateral dimension. By confining photons in the vertical direction through total internal reflection at the semiconductor-dielectric interface, the light travels laterally through extended path lengths within the quantum well layer, dramatically increasing absorption probability without increasing the physical thickness of the cell.
Solution Approach 2:
The patent changes the optical parameters of the structure by introducing a dielectric layer with specific refractive index properties that enables waveguide mode formation. This parameter change transforms the optical behavior from simple vertical transmission to complex lateral waveguide propagation, extending the effective light path length by orders of magnitude.
3Adaptability or versatility
If narrow energy-gap material is inserted to improve low energy spectral response, then absorption of low energy photons improves, but operating voltage decreases and power conversion efficiency reduces
Solution Approach 1:
The patent applies the narrow bandgap quantum well material only in specific localized regions where photon absorption is needed, rather than using it throughout the entire cell structure. The quantum wells are embedded as thin layers within the wider bandgap semiconductor matrix, allowing local optimization of spectral response without globally compromising the operating voltage determined by the dominant wider bandgap material.
Solution Approach 2:
The patent creates a composite structure combining narrow bandgap quantum well material with wider bandgap semiconductor material. This composite configuration allows the narrow bandgap component to absorb low energy photons while the wider bandgap component maintains the overall operating voltage, achieving a synergistic effect that improves spectral response without sacrificing power output.
4Quantity of substance
If optically-thin structures are used to reduce material costs and improve robustness, then material costs decrease and radiation tolerance increases, but absorption completeness decreases
Solution Approach 1:
The patent compensates for the reduced physical thickness of optically-thin structures by extending the light path in the lateral dimension through waveguide modes. This allows photons to traverse the thin quantum well layer multiple times via total internal reflection, achieving high absorption completeness despite the minimal material thickness and maintaining both cost efficiency and optical performance.
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 configuration increases photocurrent generation and maintains high open circuit voltage, achieving high efficiency and robustness while reducing material costs and radiation sensitivity.
Implementation Method 1
at least one thick well, that is equal to or greater than the thickness at which quantum confinement effect becomes negligible
Implementation Method 2
photovoltaic solid state semiconductor devices, commonly known as solar cells, convert sunlight into electrical power by generating both a current and a voltage upon illumination
Implementation Method 3
By incorporating light trapping structures, optically-thin solar cells can match or even exceed the performance of optically thick photovoltaic devices
Data Source
AI summary
Optically-thin, quantum-structured solar cells incorporating III-V quantum wells or quantum dots have the potential to revolutionize the performance of photovoltaic devices. Enhanced spectral response characteristics have been widely demonstrated in both quantum well and quantum dot solar cells using a variety of different III-V materials. To fully leverage the extended spectral response of quantum-structured solar cells, new device designs are disclosed that can both maximize the current generating capability of the limited volume of narrow band gap material and minimize the unwanted carrier recombination that degrades the voltage output.