Graded CdZnTe Buffer Layer for Photovoltaic Lattice Mismatch
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Solution Overview
Problem
Lattice mismatch between semiconductor absorber and reflector layers in photovoltaic devices leads to power dissipation and reduced power conversion efficiency due to misorientation, film cracking, and point defects, negating the benefits of the reflector layer.
Innovation Solution
Introducing an intermediate semiconductor layer with a graded or stepwise lattice constant, such as Cd(1−x)Zn(x)Te, between the cadmium telluride and zinc telluride layers to minimize lattice mismatch and facilitate electron reflection, thereby reducing recombination losses and increasing open-circuit voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a semiconductor reflector layer is deposited between the absorber layer and back contact to reduce power dissipation, then power conversion efficiency is improved, but lattice mismatch causes misorientation, film cracking, and point defects that reduce efficiency
Solution Approach 1:
A buffer layer comprising cadmium zinc telluride (CdZnTe) is introduced between the cadmium telluride absorber layer and the zinc telluride reflector layer. This intermediate buffer layer serves as a mediator that gradually transitions the lattice constant from the absorber layer to the reflector layer, reducing lattice mismatch and preventing misorientation, film cracking, and point defects while maintaining the electron reflection function.
Solution Approach 2:
The buffer layer uses cadmium zinc telluride with a graded composition where the zinc mole fraction varies through the layer thickness. This parameter change in lattice constant allows for a gradual transition between the absorber and reflector layers, minimizing lattice mismatch and associated defects while preserving the reflector's ability to reduce power dissipation.
2Productivity
If a reflector layer with lower electron affinity is used to force electron carrier flow back toward the absorber layer, then recombination at the back contact is minimized, but lattice mismatch reduces desired electron reflection
Solution Approach 1:
The cadmium zinc telluride buffer layer acts as an intermediary that maintains the electron reflection function while reducing lattice mismatch. By providing a gradual lattice constant transition, it prevents misorientation and film cracking that would otherwise reduce electron reflection effectiveness, thereby preserving power conversion efficiency.
Solution Approach 2:
The buffer layer is composed of a composite material system (CdZnTe) that combines properties of both the absorber layer (CdTe) and reflector layer (ZnTe). This composite approach allows for tailored electron affinity and lattice constant properties that maintain electron reflection while minimizing defects.
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 intermediate layer significantly reduces lattice mismatch and recombination losses, enhancing power conversion efficiency and maintaining high built-in potential in photovoltaic devices by promoting efficient electron reflection and ohmic contact.
Implementation Method 1
lattice mismatch between the reflector layer and the absorber layer can partially negate this benefit. Semiconductor materials contain a lattice, or a periodic arrangement of atoms specific to a given material. Lattice mismatching refers to a situation wherein two materials featuring different lattice constants
Implementation Method 2
some minority electron carriers penetrate through the absorber layer to a back contact adjacent to the semiconductor layer where they combine with hole carriers, causing power dissipation inside the device
Implementation Method 3
The reflector layer is made of a semiconductor material with electron affinity lower than that of the absorber layer, which forces electron carrier flow back toward the electron absorber layer, minimizing recombination at the back contact
Implementation Method 4
The semiconductor window layer, for example, a cadmium sulfide layer, can allow the penetration of solar radiation to the absorber layer, for example, a cadmium telluride layer, for conversion of solar energy to electricity
Data Source
AI summary
An improved photovoltaic device and methods of manufacturing the same that includes an interface layer adjacent to a semiconductor absorber layer, where the interface layer includes a material in the semiconductor layer which decreases in concentration from the side of the interface layer contacting the absorber layer to an opposite side of the interface layer.