Photovoltaic Absorber Layers with Nonlinear Selenium Gradients

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Solution Overview

Problem

Thin film solar cells, such as CdTe/CdS heterojunction-based photovoltaic cells, suffer from low conversion efficiency due to optical losses and high defect density at the interface, which can be exacerbated by a lattice mismatch and the need for a thin window layer to reduce absorption, leading to performance loss.

Innovation Solution

Incorporating a photovoltaic device with an absorber layer made of selenium, where the atomic concentration of selenium varies non-linearly across its thickness, allowing for a non-uniform distribution that enhances light absorption and reduces defects, potentially eliminating the need for a cadmium sulfide layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the window layer is made thin to reduce optical losses by absorption, then light absorption efficiency improves, but open circuit voltage and fill factor decrease

Engineering Contradiction:

Improveoptical lossesVSAvoidopen circuit voltage and fill factor

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent changes the composition parameter of the absorber layer by incorporating selenium with a non-linear concentration gradient. This modifies the optical and electrical properties of the absorber layer to compensate for the reduced window layer thickness, maintaining Voc and FF while reducing optical losses.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies local quality by creating a non-uniform selenium distribution within the absorber layer. The selenium concentration varies non-linearly through the layer thickness, with different regions having different compositions optimized for their specific functions: light absorption, carrier generation, and electrical property control.

Inventive Principle:

Principle #3Local quality

2Reliability

If a cadmium sulfide window layer is used to form heterojunction, then device structure is established, but production cost increases and optical losses occur

Engineering Contradiction:

Improveheterojunction formationVSAvoidproduction cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent extracts or eliminates the cadmium sulfide window layer from the device structure. By incorporating selenium directly into the absorber layer with appropriate concentration gradients, the device achieves the necessary heterojunction functionality without requiring the separate CdS window layer, thereby reducing production cost and material complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the functions of the window layer and absorber layer by incorporating selenium-modified absorber layers that simultaneously perform light absorption, carrier generation, and heterojunction formation. This consolidation eliminates the need for separate layers and reduces overall device complexity.

Inventive Principle:

Principle #5Merging (Combining)

3Ease of manufacture

If uniform selenium distribution is used in absorber layer, then manufacturing is simplified, but light absorption and defect reduction are insufficient

Engineering Contradiction:

Improveselenium distribution controlVSAvoidlight absorption efficiency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the concentration parameter of selenium non-uniformly across the absorber layer thickness. This parameter gradient is specifically designed to enhance light absorption in certain regions while controlling defect formation and electrical properties in other regions.

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

The non-linear selenium concentration improves the photovoltaic device's efficiency by increasing incident radiation absorption, enhancing passivation of grain boundaries, and reducing surface recombination, while potentially lowering production costs by minimizing or eliminating the cadmium sulfide layer.

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

Methodology Applied

Scientific EffectPhotovoltaic effect: Photovoltaic Effect

Implementation Method 2

Absorption of light by the window layer may be one of the phenomena limiting the conversion efficiency of a PV device

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Data Source

PatentEP4583668A1Photovoltaic devices

Publication Date: 2025.07.09 FIRST SOLAR INC

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AI summary

A photovoltaic device is presented. The photovoltaic device includes a layer stack; and an absorber layer is disposed on the layer stack. The absorber layer includes selenium, and an atomic concentration of selenium varies non-linearly across a thickness of the absorber layer. A method of making a photovoltaic device is also presented.