Photovoltaic Window Layer Segmentation for Diffusion Control

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Solution Overview

Problem

Thin film solar cells, such as CdTe/CdS photovoltaic devices, face challenges with inhomogeneous diffusion of sulfur or tellurium between the window and absorber layers, leading to discontinuous window layers and incomplete interface passivation, which affects device performance and stability.

Innovation Solution

A photovoltaic device configuration with a window layer comprising a low-diffusivity layer adjacent to the transparent conductive layer and a high-diffusivity layer interposed between the low-diffusivity layer and the absorber layer, allowing for controlled diffusion of sulfur or tellurium, thereby maintaining a continuous window layer and enhancing interface passivation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a thin window layer is used to maintain continuous phase, then diffusion of sulfur or tellurium is limited, but interface passivation is incomplete and device performance is reduced

Engineering Contradiction:

Improvedevice performanceVSAvoidsulfur or tellurium diffusion

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The window layer is segmented into multiple sub-layers with different compositions and thicknesses. This segmentation allows controlled diffusion pathways while maintaining an overall continuous window layer structure, enabling both adequate diffusion for passivation and structural integrity for current collection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the window layer are assigned different properties: the first sub-layer has composition optimized for diffusion control, while subsequent sub-layers have compositions optimized for maintaining continuity and electrical performance. This local quality variation enables simultaneous achievement of diffusion control and device performance.

Inventive Principle:

Principle #3Local quality

2Reliability

If high temperature processing is applied to enable sulfur or tellurium diffusion, then interface passivation improves, but unwanted diffusion into bulk window layer occurs

Engineering Contradiction:

Improveinterface passivationVSAvoidwindow layer composition

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The window layer is divided into multiple sub-layers that act as diffusion barriers and pathways. During high temperature processing, this segmentation confines sulfur or tellurium diffusion primarily to the interface region while preventing bulk diffusion, as each sub-layer provides controlled diffusion characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The multi-sub-layer structure acts as an intermediary between the absorber layer and the bulk window layer. It mediates the diffusion process by providing controlled pathways that enable necessary interface diffusion while blocking unwanted bulk diffusion during high temperature processing.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If uniform diffusion of sulfur or tellurium is achieved, then interface passivation is improved, but current density uniformity is compromised

Engineering Contradiction:

Improveinterface passivationVSAvoidcurrent density

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

Different sub-layers of the window layer are designed with different compositions and thicknesses to create local quality variations. This enables non-uniform diffusion that is optimized for each region: enhanced diffusion at the interface for passivation while maintaining appropriate diffusion levels in bulk regions to preserve current density uniformity.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The composition, thickness, and other parameters of each sub-layer are specifically optimized to control diffusion characteristics. By varying these parameters across different sub-layers, the system achieves improved interface passivation through controlled diffusion while maintaining overall current density uniformity through appropriate parameter selection in each region.

Inventive Principle:

Principle #35Parameter changes

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 configuration improves the uniformity of sulfur or tellurium diffusion at the interface, resulting in improved device performance and long-term stability by preventing unwanted diffusion into the bulk of the window layer, thus maintaining high current density and stability.

Implementation Method 1

a high-diffusivity layer interposed between the low-diffusivity layer and the absorber layer

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

a low-diffusivity layer disposed adjacent to the transparent conductive layer

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 3

The window layer allows the penetration of solar radiation to the absorber layer, where the optical energy is converted to usable electrical energy

Methodology Applied

Scientific EffectPhotovoltaic effect: Photovoltaic Effect

Data Source

PatentUS9496446B2Photovoltaic devices and method of making

Publication Date: 2016.11.15 FIRST SOLAR INC

AI summary

A photovoltaic device is presented. The photovoltaic device includes a transparent conductive layer; a window layer disposed on the transparent conductive layer; and an absorber layer disposed on the window layer. The window layer includes a low-diffusivity layer disposed adjacent to the transparent conductive layer and a high-diffusivity layer interposed between the low-diffusivity layer and the absorber layer. Method of making a photovoltaic device is also presented.