CdTe Photovoltaic Doping with Group V Elements for Stable Hole Density
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Solution Overview
Problem
CdTe-based photovoltaic devices face challenges due to low open circuit voltage, low majority carrier concentration, and short minority carrier lifetime, which limit device efficiency, and existing doping methods often result in device degradation and instability.
Innovation Solution
The method involves p-type doping of polycrystalline thin films of II-VI semiconductors with group V dopants and heat treatment in a reducing environment to achieve high hole density, incorporating the dopant into the semiconductor lattice at vacancies, promoting stable and efficient device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If copper dopants are used to increase p-type carrier concentration in CdTe, then the carrier concentration is improved, but the dopants migrate under operating conditions causing device degradation
Solution Approach 1:
The patent changes the dopant type from copper to group V elements (arsenic, antimony, phosphorus), fundamentally altering the chemical parameters of the doping system. This substitution maintains the ability to increase p-type carrier concentration while eliminating the migration and degradation issues associated with copper dopants, as group V elements form stable compounds with tellurium that do not migrate under operating conditions
Solution Approach 2:
The patent replaces the problematic copper dopant with group V element dopants that form stable, non-migrating compounds. Although the group V elements are incorporated in small concentrations, they provide stable, long-lasting doping effects without the short-term effectiveness followed by degradation that characterizes copper dopant behavior
2Quantity of substance
If Te-substitution doping is attempted in polycrystalline CdTe, then p-type doping may be achieved, but the substitution is thermodynamically unfavorable
Solution Approach 1:
The patent uses group V elements (arsenic, antimony, phosphorus) as intermediary dopants that facilitate p-type doping through a different mechanism than direct Te-substitution. These elements form stable compounds with tellurium (e.g., AsTe, SbTe, PTe) that incorporate into the CdTe lattice and provide holes as charge carriers, achieving the desired p-type conductivity without requiring thermodynamically unfavorable Te-substitution
Solution Approach 2:
The patent changes the doping mechanism from direct anion substitution (which is thermodynamically unfavorable) to compound formation with group V elements. This parameter change in the doping approach allows p-type carrier generation through a thermodynamically favorable pathway, making the manufacturing process feasible
3Ease of manufacture
If Cd evaporates readily during high temperature processing, then Te-rich and Cd-deficient films are formed, but this prevents reliable Te-substitution with group V elements
Solution Approach 1:
The patent converts the harmful effect of Cd evaporation during high temperature processing into a beneficial outcome. By using group V element dopants that form stable compounds with tellurium, the process exploits the Te-rich conditions created by Cd evaporation to facilitate dopant incorporation. The Te-rich environment promotes the formation of stable group V-teLLurium compounds that incorporate reliably into the CdTe lattice, turning the manufacturing challenge into an advantage
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 enhances charge carrier concentration and stability, improving the efficiency and long-term performance of CdTe photovoltaic devices by effectively activating group V dopants and reducing defects, leading to increased open circuit voltage and fill factor.
Implementation Method 1
Doping polycrystalline CdTe thin films with group V elements such as arsenic, antimony, or phosphorus, followed by heat treatment in a reducing environment to incorporate the dopants into the lattice, creating Te vacancies and enhancing p-type charge carrier concentration
Implementation Method 2
followed by heat treatment in a reducing environment to incorporate the dopants into the lattice
Data Source
AI summary
Provided are structures and methods for doping polycrystalline thin film semiconductor materials in photovoltaic devices. Embodiments include methods for forming and treating a photovoltaic semiconductor absorber layer.