Thermionic Emitter Work Function Tuning by Surface Photovoltage

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Solution Overview

Problem

Thermionic energy converters are limited by the high work functions of materials used, resulting in low conversion efficiencies and high operating temperatures, making them inefficient and costly due to the need for expensive materials like diamond.

Innovation Solution

A method is developed to tune the work function of thermionic emission devices by illuminating N-type semiconductor materials, using the surface photovoltage effect to lower the work function, allowing for the use of chemically stable coatings and achieving ultra-low work functions, enabling efficient electron emission at lower temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high work function materials are used in thermionic energy converters, then material stability is improved, but conversion efficiency deteriorates

Engineering Contradiction:

Improvematerial stabilityVSAvoidconversion efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies surface photovoltage illumination to dynamically change the work function parameter of the emitter material. By illuminating the emitter with photons having energy greater than the bandgap, the surface photovoltage effect reduces the work function from its original high value to a lower effective value, thereby improving conversion efficiency while maintaining material stability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite system combining a stable semiconductor material (such as silicon or gallium arsenide) with a photovoltaic coating layer. This composite structure allows the base material to provide stability while the photovoltaic layer provides work function reduction through photogenerated carriers, achieving both reliability and high efficiency

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If high work function materials are used in thermionic energy converters, then material availability is improved, but operating temperature increases

Engineering Contradiction:

Improvematerial availabilityVSAvoidoperating temperature

Core Design Contradiction:

Adaptability or versatilityVSTemperature

Solution Approach 1:

The surface photovoltage effect dynamically changes the emission characteristics of the material by reducing the work function under illumination. This allows common semiconductor materials to emit electrons at lower temperatures than would be required for traditional high work function materials, reducing operating temperature while maintaining material availability

Inventive Principle:

Principle #35Parameter changes

3Productivity

If expensive materials like diamond are used in thermionic energy converters, then emission performance is improved, but cost increases

Engineering Contradiction:

Improveemission performanceVSAvoidmaterial cost

Core Design Contradiction:

ProductivityVSEase of manufacture

Solution Approach 1:

The patent replaces expensive long-lived materials like diamond with cheaper semiconductor materials that achieve comparable or superior emission performance through the surface photovoltage effect. The photovoltaic coating layer provides the necessary work function reduction at much lower cost, making the system economically viable while maintaining high emission performance

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

Instead of relying on inherently low work function materials like diamond, the patent uses parameter changes through phot illumination to achieve low effective work function values with inexpensive semiconductor materials. This transforms the emission characteristics dynamically, achieving high performance without the high material cost

Inventive Principle:

Principle #35Parameter changes

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 the efficiency of thermionic energy converters to over 40% and enables room temperature electron emission, opening new applications and reducing material costs by achieving record-low work functions with simpler, more stable coatings.

Implementation Method 1

A method is developed to tune the work function of thermionic emission devices by illuminating N-type semiconductor materials, using the surface photovoltage effect to lower the work function

Methodology Applied

Scientific EffectSurface photovoltage effect: Photovoltaic Effect

Implementation Method 2

Thermionic energy converters offer the prospect of converting high temperature heat in a relatively high temperature range directly to electricity

Methodology Applied

Scientific EffectThermionic emission: Thermionic Emission

Data Source

PatentUS12046439B2Method for tuning work function using surface photo voltage and producing ultra-low-work-function surfaces, and devices operational therewith

Publication Date: 2024.07.23 THE BOARD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIV

AI summary

The embodiments provide a thermionic emission device and a method for tuning a work function in a thermionic emission device is provided. The method includes illuminating an N type semiconductor material of a first member of a thermionic emission device, wherein a work function of the N type semiconductor material is lowered by the illuminating. The method includes collecting, on one of the first member or a second member of the thermionic emission device, electrons emitted from one of the first member or the second member.