CdTe Layer Crystallization for Photovoltaic Light Transmission

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Solution Overview

Problem

Thin film photovoltaic devices, such as CdTe/CdS hetero-junction-based cells, face reduced performance due to photon loss at the transparent conductive oxide (TCO) and window layers, necessitating improved light transmission and manufacturing efficiency.

Innovation Solution

A method involving the simultaneous heat treatment of a layer stack comprising a cadmium-tin layer, a metal layer, and a window layer to transform the cadmium-tin layer from an amorphous to a crystalline phase, enhancing the optical transparency and electrical conductivity of the TCO and window layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple separate processing steps are used to deposit and treat each layer, then manufacturing precision can be maintained, but production time and cost increase significantly

Engineering Contradiction:

Improveproduction speedVSAvoidnumber of processing steps

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent combines multiple separate processing steps (deposition of TCO layer, deposition of window layer, and crystallization treatment) into a single integrated processing step. The amorphous TCO layer and window layer are deposited sequentially and then crystallized simultaneously in one heat treatment process, reducing the total number of processing steps while maintaining layer quality and interface precision.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The amorphous TCO layer is deposited first as a preliminary step before the window layer, creating a structured layer stack that is then crystallized in one subsequent treatment. This preliminary deposition of layers in a specific sequence enables the final simultaneous crystallization to achieve the desired optical and electrical properties efficiently.

Inventive Principle:

Principle #10Preliminary action

2Illumination intensity

If the TCO and window layers are kept as amorphous phases, then manufacturing is simpler, but light transmission performance is reduced

Engineering Contradiction:

Improvelight transmissionVSAvoidprocessing temperature

Core Design Contradiction:

Illumination intensityVSTemperature

Solution Approach 1:

The patent utilizes phase transition from amorphous to crystalline state through controlled heat treatment. The simultaneous crystallization of the TCO and window layers transforms their structural phase, significantly improving light transmission performance. The phase transition is achieved at a specific temperature range that crystallizes both layers without damaging the device structure.

Inventive Principle:

Principle #36Phase transitions

3Manufacturing precision

If separate heat treatment steps are used for TCO and window layers, then each layer can be optimized independently, but production time increases

Engineering Contradiction:

Improvelayer optimizationVSAvoidprocessing time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent merges separate heat treatment steps for TCO and window layers into a single simultaneous crystallization process. By carefully controlling the heating parameters, both layers are crystallized together in one treatment step, reducing total processing time while maintaining the ability to optimize each layer's crystallization characteristics through parameter selection.

Inventive Principle:

Principle #5Merging (Combining)

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 improved light transmission and device performance by crystallizing the TCO and window layers in a single step, reducing production costs and enhancing the efficiency of photovoltaic devices.

Implementation Method 1

The heating step comprises transforming at least a portion of the first layer from an amorphous phase to a crystalline phase

Methodology Applied

Scientific EffectPhase transformation (amorphous to crystalline): Phase Change

Implementation Method 2

transforming at least a portion of the first layer from an amorphous phase to a crystalline phase

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Implementation Method 3

heating a layer stack that includes a first layer comprising cadmium and tin

Methodology Applied

Scientific EffectThermal heating: Heating

Data Source

PatentUS9034686B2Manufacturing methods for semiconductor devices

Publication Date: 2015.05.19 FIRST SOLAR INC

AI summary

Embodiments of the present invention include a method. The method includes heating a layer stack. The layer stack includes a first layer comprising cadmium and tin, a metal layer disposed over the first layer, and a window layer disposed over the metal layer. Heating the stack includes transforming at least a portion of the first layer from an amorphous phase to a crystalline phase. Heating may be performed using any of various configurations, such as, for example, heating an individual stack, or using a face-to-face configuration of multiple stacks. The stack may be used for fabricating a photovoltaic device.