Solar Cell Annealing With Lithium Passivation for Radiation Damage
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Solution Overview
Problem
Solar cells deployed in extreme environments, such as space, experience efficiency loss due to radiation exposure and defects, which existing annealing methods fail to effectively recover, leading to reduced power production.
Innovation Solution
The method involves orienting solar cell arrays towards the sun, open-circuiting portions to raise temperature, and using lithium to passivate defects through controlled electric fields and additional current or light sources, with embedded resistors or heaters to enhance annealing, and incorporating lithium into silicon cells to maintain efficiency over the cell's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solar cells are operated in extreme environments (space, high radiation), then power production is initially high, but efficiency is lost over time due to radiation-induced defects
Solution Approach 1:
Lithium is pre-diffused into the silicon solar cell structure before deployment, creating a reservoir of mobile lithium atoms that will automatically migrate to and passivate radiation-induced defects when they form, preventing efficiency loss before it occurs
Solution Approach 2:
The solar cell uses its own operational conditions (temperature, electrical bias, light illumination) to drive lithium diffusion and defect passivation, enabling self-healing without external intervention or additional system complexity
2Reliability
If traditional annealing methods are used to recover efficiency, then some performance can be restored, but the process is too slow and impractical for space applications
Solution Approach 1:
The invention changes the physical and chemical parameters of the silicon lattice by introducing lithium atoms that alter defect formation energies and migration barriers, enabling rapid defect passivation at operational temperatures rather than requiring prolonged high-temperature annealing
Solution Approach 2:
The invention replaces the mechanical/thermal annealing process (requiring external heating equipment and long durations) with a chemical field effect where lithium atoms diffuse and bind to defects, achieving the same recovery goal through a different physical mechanism that is much faster
3Reliability
If high temperatures are applied to anneal defects, then efficiency recovery is improved, but energy consumption increases and may damage other components
Solution Approach 1:
The solar cell undergoes periodic or continuous low-level heating during operation that maintains lithium mobility for defect passivation without requiring high-temperature spikes, distributing the thermal energy input over time at lower intensities
Solution Approach 2:
Lithium atoms act as intermediary species that mediate between the silicon lattice and radiation-induced defects, enabling efficiency recovery through chemical binding rather than direct thermal annealing, thus reducing the need for high energy input
4Reliability
If lithium is added to passivate defects, then efficiency stability is improved, but manufacturing complexity increases
Solution Approach 1:
The invention merges the lithium diffusion step with the existing solar cell fabrication process, incorporating lithium into the silicon material during crystal growth or subsequent processing steps that are already part of standard manufacturing workflows
Solution Approach 2:
Lithium is introduced at specific locations and concentrations within the silicon structure (such as near expected defect regions or at interfaces), providing targeted passivation capability without requiring uniform lithium distribution throughout the entire cell, thus simplifying manufacturing
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 allows for rapid and efficient recovery of solar cell efficiency, extending mission durations and increasing energy production by minimizing energy used for annealing while maintaining high power conversion efficiency.
Implementation Method 1
Lithium has been used to passivate radiation induced defects and therefore recover power conversion efficiency of those cells. Hydrogen is also known to be a highly mobile species in silicon and is used in silicon solar cell and microelectronic device manufacturing to passivate defects
Implementation Method 2
when these devices are heated to elevated temperatures, some of the damage accumulated in these devices can be annealed leading to recovery of a portion of the energy conversion efficiency that was lost
Implementation Method 3
Damage to such cells is caused by energetic particles and high energy photons that are incident on the cells in the space environment, leading to displacement of atoms and creation of defects. These defects then cause trapping and recombination of photo-generated carriers
Data Source
AI summary
Method and apparatus for annealing solar cells that can contain lithium or hydrogen. Heaters, a current that is applied in forward or reverse direction, or open-circuiting the cells are used optionally with illumination from the sun or a controlled light source, which can be directed using reflectors, to increase the temperature of the cells to perform periodic anneals to recover energy conversion efficiency lost due to environmental conditions such as radiation damage and maintain desired operational conditions. Larger amounts of additional energy are harvested with the improved efficiency of the cells. Illuminating the cells with specific wavelengths of light can enhance the diffusion of the lithium or hydrogen, or their binding and unbinding from dopants or defects, in the silicon lattice. The lithium or hydrogen can diffuse into the cells via their inclusion in the polysilicon layer forming a tunneling oxide passivated contact. Dopants in the silicon can reduce annealing time and temperature.