SWNT Back Contact Layer for CdTe Photovoltaic Cells
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Solution Overview
Problem
Cadmium Telluride (CdTe) photovoltaic cells face performance degradation due to copper diffusion, which leads to shunt defects, reduced fill factor, and lower energy conversion efficiency, necessitating the development of a barrier layer that prevents copper migration and forms an ohmic contact without using copper.
Innovation Solution
A photovoltaic cell structure incorporating a single-wall carbon nanotube (SWNT) layer as a back contact, which inhibits copper diffusion and forms a low potential energy barrier for electrical current flow, eliminating the need for copper and using a metallic layer like Au, Mo, Ti, or Cr to enhance conductivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used to form a back contact in CdTe photovoltaic cells, then electrical conductivity is improved, but copper diffusion causes shunt defects and performance degradation
Solution Approach 1:
A carbon-based intermediate layer is introduced between the metal back contact and the CdTe semiconductor layer. This intermediary prevents direct contact between copper and CdTe, blocking copper diffusion while maintaining electrical conductivity through the carbon layer's conductive properties.
Solution Approach 2:
Copper is completely removed from the back contact structure. Instead of using copper or copper-containing materials, the invention employs alternative metals (Al, Ti, Mo, Ni, etc.) combined with a carbon-based layer, extracting the harmful element while preserving the necessary electrical function.
2Reliability
If copper-free back contact structures are used to prevent shunt defects, then reliability is improved, but electrical conductivity and contact quality deteriorate
Solution Approach 1:
The back contact structure uses a composite of metal layer and carbon-based material. The metal provides structural stability and initial conductivity, while the carbon layer enhances conductivity and prevents copper diffusion, creating a synergistic structure that achieves both low resistance and high reliability.
Solution Approach 2:
The carbon layer undergoes graphitization treatment to transform its crystalline structure, dramatically improving electrical conductivity. This parameter change (from amorphous to crystalline graphite structure) reduces series resistance while maintaining the copper-blocking function.
3Productivity
If thin layer semiconductor materials are used to reduce materials usage and weight, then manufacturing efficiency is improved, but defect impact becomes more pronounced
Solution Approach 1:
The carbon-based back contact layer is prepared in advance with optimized properties (conductivity, adhesion, copper-blocking capability) before the thin CdTe layer is deposited. This preliminary preparation ensures that the thin semiconductor layer has a high-quality interface, minimizing defect formation during subsequent processing.
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 SWNT layer improves open-circuit voltage, fill factor, and energy conversion efficiency, while maintaining thermal stability and reducing series resistance, thus enhancing the performance and durability of CdTe-based photovoltaic cells.
Implementation Method 1
the SWNT layer is configured to inhibit or preclude the migration of deleterious elements or species into the CdTe... the SWNT back contact has a characteristic defined by a low potential energy barrier to electrical current flow
Implementation Method 2
A photovoltaic cell structure incorporating a single-wall carbon nanotube (SWNT) layer as a back contact, which inhibits copper diffusion
Data Source
AI summary
A photovoltaic cell structure is disclosed that includes a back contact layer that includes single wall carbon nanotube elements. The single wall carbon nanotube (SWNT) back contact is in electrical communication with an adjacent semiconductor layer and provides a buffer characteristic that impedes elemental metal migration from the back contact into the semiconductor active layers. In one embodiment, the SWNT back contact includes a semiconductor characteristic and a buffer characteristic. In another embodiment, the SWNT back contact further includes a metallic characteristic.