Transient Photoluminescence Mapping for Solar Cell Characterization
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Solution Overview
Problem
Existing photoluminescence imaging systems for solar cell fabrication are complex and expensive, requiring sophisticated light sources and filters, and sensitive cameras to measure photogeneration rate and carrier lifetime in silicon solar cells.
Innovation Solution
A simplified photoluminescence mapping system that uses a non-coherent light source, such as a flash or LEDs, and a less sensitive camera, with controlled exposure and time delays to capture photoluminescence signals, eliminating the need for complex filtering systems and allowing for the use of less expensive equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a steady-state coherent light source (laser) is used to stimulate photogeneration of carriers, then photogeneration rate and carrier lifetime can be measured, but the system becomes complex and expensive requiring sophisticated filtering systems and high sensitivity cameras
Solution Approach 1:
The patent applies periodic action by using pulsed illumination instead of continuous steady-state light sources. The illumination source emits light in periodic pulses, allowing the photoluminescence signal to be captured during specific time windows when the stimulation light is not present. This temporal separation eliminates the need for complex filtering systems while maintaining measurement precision for photogeneration rate and carrier lifetime
Solution Approach 2:
The patent implements preliminary action by capturing the photoluminescence signal during a predetermined time period immediately following the illumination pulse. By anticipating and capturing the signal during this specific time window before it decays, the system achieves accurate measurements without requiring high sensitivity cameras or complex filtering, as the signal is captured at its peak intensity
2Measurement precision
If a steady-state coherent light source is used, then carrier density can be estimated by monitoring radiative recombination, but expensive and complex filtering systems are required in front of the camera
Solution Approach 1:
The patent uses periodic pulsed illumination to create temporary photogeneration of carriers. By illuminating the semiconductor substrate in periodic pulses rather than continuously, the system generates carrier density variations that can be monitored during the pulse-off periods. This eliminates the need for complex filtering systems while maintaining accurate carrier density estimation through temporal signal separation
3Measurement precision
If traditional photoluminescence imaging is used, then photogeneration rate and carrier lifetime can be characterized, but the system is expensive and requires high sensitivity cameras
Solution Approach 1:
The patent implements preliminary action by capturing the photoluminescence signal during a predetermined time period immediately following the illumination pulse, when the signal intensity is at its peak. This timing strategy allows the use of less sensitive, more cost-effective camera systems while maintaining accurate characterization of photogeneration rate and carrier lifetime, eliminating the need for expensive high sensitivity cameras
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 reduces system complexity and cost, while enhancing sensitivity and accuracy for characterizing photogeneration rate and carrier lifetime in solar cell substrates, including those with low photoluminescence intensities, and enables faster testing with reduced equipment costs.
Implementation Method 1
irradiating a surface of a substrate with an illumination source for a predetermined period of time to photogenerate carriers
Implementation Method 2
characterize a photoluminescence (PL) signal emitted from the surface of the substrate generated by recombination of the carriers
Data Source
AI summary
A photoluminescence mapping system and method for use in fabricating solar cells that eliminates the need for complex and expensive light sources, filters and high sensitivity cameras. Generally, the method includes: (i) irradiating a surface of the substrate with radiation having a predetermined energy for a first predetermined period of time to photogenerate carriers therein; (ii) stopping the irradiation; (iii) exposing the surface of the substrate to a camera for a second predetermined period of time; and (iv) capturing with the camera a photoluminescence (PL) signal emitted from the surface of the substrate.