Exciton-Blocking Charge Carrier Filters for Organic Photovoltaics

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Solution Overview

Problem

Organic photovoltaic cells face challenges in achieving high conversion efficiencies due to exciton recombination and limited practical layer thickness of traditional buffers, which are highly resistive and rely on damage-induced transport states, limiting their effectiveness in enhancing charge extraction and reducing internal resistance.

Innovation Solution

The development of exciton-blocking charge carrier filters, comprising a mixture of wide energy gap materials and electron or hole conducting materials, optimized for location within the device to block excitons and facilitate charge transport, thereby reducing exciton-polaron quenching and enhancing short-circuit current and fill factor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If traditional buffer layers are used in organic photovoltaic cells, then device structure is simple, but exciton blocking is poor and charge carrier transport is resistive, leading to low short-circuit current and fill factor

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidbuffer layer composition

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent applies composite materials by creating buffer layers that combine wide energy gap materials (for exciton blocking) with electron or hole conducting materials (for charge transport). This composite approach resolves the contradiction by achieving both effective exciton blocking and low-resistance charge transport simultaneously, improving power conversion efficiency without excessive complexity

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies local quality by optimizing the buffer layer composition specifically for its location between the active layer and electrode. The wide energy gap material properties are localized to block excitons at the interface, while the conducting material properties are localized to facilitate charge extraction, creating spatially differentiated functionality within the buffer layer

Inventive Principle:

Principle #3Local quality

2Reliability

If traditional buffer layers are used, then device structure is simple, but exciton recombination occurs, reducing short-circuit current and fill factor

Engineering Contradiction:

Improveexciton blocking performanceVSAvoidbuffer layer composition

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The composite buffer layer structure combines the exciton-blocking capability of wide energy gap materials with the charge transport capability of conducting materials, achieving reliable exciton blocking without the high resistivity that plagues traditional single-material buffer layers

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The buffer layer acts as an intermediary between the active layer and electrode, using wide energy gap materials to block excitons while allowing charge carriers to pass through the conducting material component, thus mediating the interaction between light-generated excitons and the electrode

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If exciton-blocking charge carrier filters are introduced, then short-circuit current and fill factor improve, but device structure becomes more complex

Engineering Contradiction:

Improvecharge extraction efficiencyVSAvoidbuffer layer composition

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent uses composite materials to create buffer layers that simultaneously provide exciton blocking and charge transport functions, achieving improved charge extraction efficiency while keeping the added complexity manageable through a two-component system rather than multiple separate layers

Inventive Principle:

Principle #40Composite materials

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

These filters improve the efficiency of organic photovoltaic cells by increasing short-circuit current and fill factor while maintaining open-circuit voltage, leading to enhanced power conversion efficiency and reduced internal resistance, even at thicker layer thicknesses.

Implementation Method 1

block excitons and facilitate charge transport

Methodology Applied

Scientific EffectExciton blocking:

Implementation Method 2

facilitate charge transport

Methodology Applied

Scientific EffectCharge carrier transport: Conduction (electrical)

Implementation Method 3

The at least one cathode-side wide energy gap material has: a Lowest Unoccupied Molecular Orbital energy level (LUMO CS-WG) smaller than or equal to the LUMO Acc; a Highest Occupied Molecular Orbital energy level (HOMO CS-WG) larger than, equal to, or within 0.3 eV smaller than the HOMO Acc; and a HOMO CS-WG-LUMO CS-WG energy gap wider than a HOMO Acc-LUMO Acc energy gap

Methodology Applied

Scientific EffectWide energy gap absorption: Absorption (EM radiation)

Data Source

PatentEP3726579A1Organic photosensitive devices with exciton-blocking charge carrier filters

Publication Date: 2020.10.21 FORREST STEPHEN R

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AI summary

Disclosed herein are organic photosensitive devices including a first subcell and a second subcell and having at least one exciton-blocking charge carrier filter disposed between the subcells. The filters comprise a mixture of at least one wide energy gap material and at least one electron or hole conducting material. As described herein, the filters simultaneously block excitons and conduct the desired charge carrier (electrons or holes).