CdTe Solar Cell Minority Carrier Lifetime via Te-Rich Deposition
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Solution Overview
Problem
Current methods for producing polycrystalline CdTe solar cells are limited by short minority carrier lifetimes and defects, which restrict the enhancement of open-circuit voltage (Voc) and overall device performance.
Innovation Solution
A method involving the deposition of polycrystalline CdTe layers with non-stoichiometric ratios of Cd and Te, allowing for the incorporation of additional elements as dopants, which reduces recombination-related defects and enhances minority carrier lifetime, resulting in improved device efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional deposition methods are used to produce polycrystalline CdTe, then manufacturing process is simple, but minority carrier lifetime is short (≤2 ns)
Solution Approach 1:
The patent applies parameter changes by depositing CdTe layers with non-stoichiometric compositions (specifically Te-rich compositions with excess tellurium). This compositional parameter change fundamentally alters the material properties, reducing recombination-related defects and extending minority carrier lifetime from ≤2 ns to >10 ns, thereby resolving the contradiction between simple manufacturing and long carrier lifetime.
2Reliability
If net acceptor concentration is increased to enhance Voc, then open circuit voltage improves, but device fill factor decreases due to reduced depletion width
Solution Approach 1:
The patent changes the compositional parameter of CdTe to Te-rich non-stoichiometric composition, which simultaneously increases net acceptor concentration (improving Voc) and extends minority carrier lifetime (maintaining fill factor). The extended carrier lifetime compensates for the reduced depletion width effect, allowing both parameters to improve together rather than trade off against each other.
Solution Approach 2:
The patent creates a composite material system by incorporating excess tellurium into the CdTe lattice, forming a Te-rich polycrystalline structure. This composite approach with controlled compositional ratios enables simultaneous optimization of electrical properties (Voc) and optical properties (fill factor) that cannot be achieved with stoichiometric CdTe alone.
3Quantity of substance
If Cu is diffused into CdTe layer to increase net acceptor density, then NA increases above typical values, but Cu also diffuses into CdS layer reducing net donor densities
Solution Approach 1:
The patent applies preliminary action by pre-forming the Te-rich CdTe layer with extended minority carrier lifetime before any Cu diffusion occurs. This preliminary structural optimization creates a more tolerant system that can withstand Cu diffusion without severe performance degradation, and the extended carrier lifetime compensates for any negative effects on donor density in the CdS layer.
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 approach increases minority carrier lifetime to over 10 ns and achieves higher net acceptor or donor concentrations, leading to enhanced efficiency in CdTe photovoltaic cells.
Implementation Method 1
a method of depositing a layer of material including polycrystalline CdTe onto a substrate
Implementation Method 2
providing to a deposition process one or more source materials that includes an amount of Cd and an amount of Te in a non-stoichiometric ratio... the resulting polycrystalline CdTe may have a minority carrier lifetime of at least about 10 ns
Data Source
AI summary
A method of producing polycrystalline CdTe materials and devices that incorporate the polycrystalline CdTe materials are provided. In particular, a method of producing polycrystalline p-doped CdTe thin films for use in CdTe solar cells in which the CdTe thin films possess enhanced acceptor densities and minority carrier lifetimes, resulting in enhanced efficiency of the solar cells containing the CdTe material are provided.