Graded CdTe Absorber Layer for Photovoltaic Efficiency
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Solution Overview
Problem
Cadmium telluride (CdTe)-based photovoltaic devices exhibit low power conversion efficiencies due to low open circuit voltage and short minority carrier lifetime, primarily attributed to the interaction between CdS and CdTe layers, which affects carrier concentration and lifetime at the front interface.
Innovation Solution
A photovoltaic device with an absorber layer comprising two regions, one optimized for carrier lifetime and the other for carrier density, using additives such as oxygen and nitrogen or zinc, with a graded concentration profile to improve interface properties and charge carrier collection, decoupling the interaction between CdS and CdTe layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If doping with p-type dopants is used to improve effective carrier concentration of CdTe, then carrier density increases, but carrier lifetime decreases
Solution Approach 1:
The absorber layer is divided into two distinct regions: a first region adjacent to the window layer with lower carrier density optimized for long carrier lifetime, and a second region with higher carrier density optimized for charge collection. This segmentation allows each region to have optimized properties without the trade-off present in uniformly doped structures.
Solution Approach 2:
Different regions of the absorber layer are assigned different doping concentrations and additive compositions tailored to their specific functional requirements. The first region has properties optimized for carrier generation and long lifetime, while the second region has properties optimized for carrier collection, creating local quality variations that resolve the global trade-off.
2Duration of action of moving object
If the interface between CdS and CdTe is improved to increase minority carrier lifetime, then carrier lifetime increases, but this may reduce carrier density
Solution Approach 1:
The absorber layer is segmented into a first region optimized for interface quality and long carrier lifetime, and a second region optimized for high carrier density. This allows the interface region to have properties favoring long lifetime without compromising the overall carrier density of the device.
Solution Approach 2:
The first region adjacent to the CdS window layer is given specific compositional characteristics including lower dopant concentration and presence of first additives to optimize interface quality and carrier lifetime, while the second region has different composition optimized for carrier density, creating local quality differences that resolve the contradiction.
3Ease of manufacture
If a single uniform absorber layer composition is used, then manufacturing is simpler, but power conversion efficiency is limited
Solution Approach 1:
The absorber layer is segmented into two regions with different compositions and properties, allowing optimization of both carrier lifetime and carrier density for improved power conversion efficiency. The segmentation can be implemented through controlled deposition conditions that maintain relative manufacturing simplicity while achieving performance benefits.
Solution Approach 2:
The composition parameters of the absorber layer are changed across different regions, including dopant concentration, additive types and concentrations. These parameter variations enable optimization of electrical properties for improved efficiency while maintaining a relatively simple two-region structure that does not overly complicate manufacturing.
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 solution enhances minority carrier lifetimes and carrier densities, leading to increased photovoltaic device efficiencies by optimizing the interface between the window and absorber layers, resulting in higher power conversion efficiencies.
Implementation Method 1
The window layer allows the penetration of solar radiation to the absorber layer, where the optical energy is converted to usable electrical energy.
Data Source
AI summary
In one aspect of the present invention, a photovoltaic device is provided. The photovoltaic device includes a window layer and an absorber layer disposed on the window layer, wherein the absorber layer includes a first region and a second region, the first region disposed adjacent to the window layer. The absorber layer further includes a first additive and a second additive, wherein a concentration of the first additive in the first region is greater than a concentration of the first additive in the second region, and wherein a concentration of the second additive in the second region is greater than a concentration of the second additive in the first region. Method of making a photovoltaic device is also provided.