Pseudomorphically Strained Electron Reflector Layer in CdTe Solar Cells
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Solution Overview
Problem
Polycrystalline CdTe solar cells face challenges in preventing recombination of photo-generated electrons with holes near the back contact region, leading to increased recombination in the absorber bulk, higher materials costs, and decreased manufacturing throughput.
Innovation Solution
Incorporating a pseudomorphically strained electron reflector layer, such as a graded CdMgTe, CdZnTe, or CdMnTe layer, between the p-type semiconductor layers to act as an energy barrier and reduce electron recombination, allowing for thinner absorber layers and improved charge collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick CdTe absorber layer (2-5 μm) is used to prevent recombination at the back contact, then recombination prevention is improved, but materials cost increases and manufacturing throughput decreases
Solution Approach 1:
The absorber layer is segmented into multiple thinner sub-layers (first p-type semiconductor layer, second p-type semiconductor layer, and third p-type semiconductor layer) instead of using a single thick layer. This segmentation maintains effective recombination prevention while reducing the total absorber thickness from 2-5 μm to approximately 1-2 μm, thereby improving manufacturing throughput without sacrificing reliability.
2Reliability
If a thick CdTe absorber layer is used to prevent recombination at the back contact, then recombination prevention is improved, but materials cost increases
Solution Approach 1:
The absorber is divided into multiple thinner p-type semiconductor layers that collectively provide the same recombination prevention function as a single thick layer. This reduces the total quantity of CdTe material required, lowering materials cost while maintaining the necessary recombination prevention performance through the distributed layer structure.
3Productivity
If the absorber layer thickness is reduced to improve manufacturing throughput, then productivity is improved, but recombination increases
Solution Approach 1:
The absorber is segmented into multiple thin p-type semiconductor layers separated by interfaces that act as recombination barriers. This segmentation maintains effective recombination prevention even at reduced total thickness, enabling thinner absorbers (1-2 μm) to achieve both improved productivity and maintained reliability.
Solution Approach 2:
The interfaces between the segmented p-type semiconductor layers serve as intermediary recombination barriers. These interfaces prevent electron-hole recombination that would otherwise occur in a continuous thick layer, allowing the use of thinner absorber material while maintaining recombination prevention effectiveness.
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 the open-circuit voltage and fill factor of solar cells while maintaining a dislocation-free interface, reducing recombination rates and improving overall device performance.
Implementation Method 1
electron reflectors can be utilized by using a step change in doping p/p+ near the back p-type ohmic contact to increase band bending in the conduction/valence bands at the doping transition
Implementation Method 2
Incorporating a pseudomorphically strained electron reflector layer, such as a graded CdMgTe, CdZnTe, or CdMnTe layer
Implementation Method 3
Charge carriers are generated in the absorber layer by the absorption of photons of light therein, which are subsequently driven towards one or more contacts within the cell
Implementation Method 4
Photogenerated minority carriers move within the semiconductor layer in which they were created as driven by diffusion and drift
Implementation Method 5
Photogenerated minority carriers move within the semiconductor layer in which they were created as driven by diffusion and drift
Data Source
AI summary
Solar cells, absorber structures, back contact structures, and methods of making the same are described. The solar cells and absorber structures include a pseudomorphically strained electron reflector layer.