Solar Cell Base Thickness and DBR for Radiation Hardening
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Solution Overview
Problem
Current solar cell designs, such as those described in U.S. Patent No. 9,252,313, fail to maintain performance effectively at high radiation doses above 1e15 e-/cm², necessitating the development of optimized solar cells for improved performance in high radiation environments.
Innovation Solution
A solar cell design featuring a sub-cell with a base thickness of about 2 to 3 µm, p-type doping of 1e14 cm⁻³ to 1e16 cm⁻³, and a distributed Bragg reflector inserted behind the sub-cell to maximize current generation, optimizing performance at high radiation doses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the base thickness is reduced to 2-3 μm and doping is lowered to 1e14 cm⁻³, then radiation dose performance is improved, but light absorption capability deteriorates
Solution Approach 1:
A distributed Bragg reflector (DBR) is introduced as an intermediary component between the thinned base and the emitter. The DBR reflects unabsorbed photons back into the base, enabling multiple passes through the thin base region and enhancing light absorption without requiring increased base thickness. This resolves the contradiction by mediating between the thin base structure (for radiation resistance) and light absorption requirements.
Solution Approach 2:
The DBR enables continuous light absorption by reflecting photons that pass through the thin base back into the absorption region. Instead of a single pass through the base, photons undergo multiple absorption opportunities, maintaining effective light harvesting despite the reduced base thickness. This continuity compensates for the reduced absorption path length.
2Productivity
If a distributed Bragg reflector is added to enhance current generation, then beginning-of-life efficiency is improved, but device complexity increases
Solution Approach 1:
The DBR is designed with specific layer thicknesses and material compositions tailored to the solar cell's operating wavelength range. By optimizing the DBR parameters (layer thickness, refractive index contrast, number of periods), high reflectivity is achieved at target wavelengths while maintaining compatibility with the underlying thin base structure. This parameter optimization enhances efficiency without excessive complexity.
3Reliability
If the base is thinned to reduce radiation damage, then end-of-life power retention is improved, but manufacturing precision requirements increase
Solution Approach 1:
The DBR structure provides self-aligning properties during fabrication. The DBR layers are deposited epitaxially on the thinned base, and the reflector's optical function is relatively insensitive to small variations in base thickness. This self-service characteristic reduces the stringency of thickness control requirements compared to designs without a DBR, as the DBR compensates for minor thickness variations through its broadband reflectivity.
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
The new solar cell design achieves a 4% relative improvement in beginning-of-life efficiency and a 12% relative improvement in end-of-life power retention at high radiation doses, exceeding previous state-of-the-art performance.
Implementation Method 1
a distributed Bragg reflector inserted behind the sub-cell to maximize current generation
Implementation Method 2
solar cell design featuring a sub-cell with a base thickness of about 2 to 3 µm, p-type doping of 1e14 cm⁻³ to 1e16 cm⁻³
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A solar cell optimized for performance at high radiation doses, wherein the solar cell includes: a sub-cell comprised of a base and an emitter; the base of the sub-cell has a thickness of about 2 to 3 µm; the base of the sub-cell is doped at about 1e14 cm-3 to 1e16 cm-3; and a reflector is inserted behind the sub-cell to maximize current generated by the sub-cell.