CdTe Back Contact Stability via Simultaneous Te Enrichment and Cu Doping
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Solution Overview
Problem
Conventional metal back contacts for CdTe photovoltaic cells degrade over time, leading to efficiency loss due to the high work function of cadmium telluride and the need for separate tellurium enrichment and copper doping processes, which can introduce excess copper that further degrades the device.
Innovation Solution
A method is developed to create a tellurium-enriched surface on the cadmium telluride layer using a treatment solution containing a chlorinated compound and a copper-containing metal salt, allowing for simultaneous formation of a copper-telluride phase in a single processing step, minimizing excess copper introduction and enhancing the stability of the back contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional metal back contacts are used for CdTe photovoltaic cells, then the back contact can be formed, but the device degrades significantly over time due to high work function mismatch and copper degradation
Solution Approach 1:
The patent combines the tellurium enrichment process and copper doping process into a single simultaneous treatment step. The treatment solution contains both Te-rich compounds (such as TeO2, TeCl4, or (NH4)2TeO3) and Cu-containing compounds (such as CuCl2, Cu(NO3)2, or Cu acetate), allowing both functions to be achieved in one annealing process rather than requiring separate sequential steps.
Solution Approach 2:
The treatment solution serves multiple functions simultaneously: it enriches the CdTe surface with tellurium to create a Te-rich layer, introduces copper for doping, and forms copper-telluride phases all in one application and annealing cycle. This multi-functional approach simplifies the manufacturing process while improving back contact stability.
2Reliability
If separate Te enrichment and Cu doping processes are performed, then good ohmic back contact can be formed, but excess copper is introduced leading to device degradation
Solution Approach 1:
The patent controls the concentration ratios of Te-containing compounds to Cu-containing compounds in the treatment solution to optimize the amount of copper introduced. By adjusting these parameters, the process achieves sufficient copper doping for ohmic contact formation while minimizing excess copper that would cause degradation. The simultaneous process allows better control of Cu incorporation compared to separate steps.
Solution Approach 2:
The treatment solution acts as an intermediary medium that delivers both tellurium and copper to the CdTe surface in controlled amounts. The solution composition can be precisely formulated to provide the right stoichiometry, ensuring adequate copper for contact formation without introducing harmful excess copper, while the annealing process facilitates controlled diffusion and phase formation.
3Ease of manufacture
If graphite paste back contacts are used, then the back contact can be formed, but fill factor and open circuit voltage decrease over time due to shunt resistance decrease and series resistance increase
Solution Approach 1:
The patent modifies the surface properties of CdTe through chemical treatment and annealing, changing the electrical and chemical parameters at the interface. This creates a more stable interface with better ohmic contact characteristics that maintains fill factor and open circuit voltage over time, overcoming the degradation issues of conventional graphite paste contacts while retaining ease of formation.
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 results in a more stable and efficient back contact for CdTe photovoltaic cells with reduced degradation, improving long-term performance and facilitating commercialization by integrating tellurium enrichment and copper doping in a single step.
Implementation Method 1
annealing the device with the p-type absorber layer in contact with the treatment solution to form a tellurium-enriched region in the p-type absorber layer at the exposed surface
Implementation Method 2
annealing the device with the p-type absorber layer in contact with the treatment solution to form a tellurium-enriched region
Implementation Method 3
The treatment solution generally comprises a chlorinated compound component that is substantially free from copper, a copper-containing metal salt, and a solvent
Data Source
AI summary
Methods for preparing an exposed surface of a p-type absorber layer of a p-n junction for coupling to a back contact in the manufacture of a thin film photovoltaic device are provided. The method can include: applying a treatment solution onto the exposed surface defined by the p-type absorber layer of cadmium telluride; and annealing the device with the p-type absorber layer in contact with the treatment solution to form a tellurium-enriched region in the p-type absorber layer at the exposed surface. The treatment solution comprises a chlorinated compound component that is substantially free from copper, a copper-containing metal salt, and a solvent.