Organic Photovoltaic Cells with Three-Layer Heterojunction
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Solution Overview
Problem
Conventional organic photovoltaic cells have limited photocurrent generation due to narrow absorption bandwidth, and complex layer structures required for multi-junction cells lead to power matching challenges and reduced fill factor and open-circuit voltage.
Innovation Solution
An organic photovoltaic cell with a heterojunction structure comprising a first donor layer, a first acceptor layer, and an additional second acceptor or donor layer with specific optical band gaps and LUMO/HOMO levels, allowing for enhanced exciton dissociation and charge transfer mechanisms, thereby increasing photocurrent without the need for power matching and minimizing voltage loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two or more organic cells are stacked in a tandem configuration to broaden the absorption spectrum, then the photocurrent is enhanced, but the device complexity increases and power matching between cells becomes challenging
Solution Approach 1:
The patent combines a first organic photovoltaic cell with a second organic photovoltaic cell into a single integrated device structure, where the third active layer serves as the second cell. This merging approach broadens the absorption spectrum and enhances photocurrent while avoiding the complexity of separate tandem cell connections and power matching requirements.
Solution Approach 2:
The active layer is segmented into three distinct organic semiconductor layers with different band gaps, where each layer absorbs specific portions of the solar spectrum. The first and third layers have larger band gaps absorbing higher energy photons, while the second layer has a smaller band gap absorbing lower energy photons, creating a systematic division of spectral absorption responsibilities.
2Productivity
If a three-layer cascade structure with an ambipolar interlayer is used to enhance photocurrent, then the photocurrent increases, but the fill factor is reduced
Solution Approach 1:
The patent assigns specific functional qualities to each layer: the first and third layers serve as donor layers with larger band gaps, while the second layer serves as an acceptor layer with a smaller band gap. This localized functional assignment enables exciton dissociation at multiple interfaces (first/second and second/third layers) without requiring a complex ambipolar interlayer, thereby maintaining good fill factor while enhancing photocurrent.
3Productivity
If a three-layer cascade structure is implemented to broaden absorption, then the photocurrent is enhanced, but the open-circuit voltage is reduced due to cascade energy levels
Solution Approach 1:
The patent optimizes the energy level parameters of the three organic semiconductor layers to achieve a balance between photocurrent enhancement and voltage maintenance. By carefully selecting materials with appropriate band gap differences and energy level alignments, the device achieves enhanced photocurrent through multi-layer absorption while minimizing voltage losses that would otherwise occur in cascade structures.
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 enables higher photocurrent generation with improved fill factor and reduced open-circuit voltage loss compared to tandem or cascade cells, achieving better performance with a simpler layer structure.
Implementation Method 1
In 'Sensitization of organic photovoltaic cells based on interlayer excitation energy transfer ', Organic Electronics 11 (2010) 700-704, M. Ichikawa et al. describe still another approach for increasing the short-circuit current density of organic photovoltaic cells. An additional p-type organic semiconductor layer (APL) is introduced into organic photovoltaic cells that have a single p/n junction formed by an indispensable p-type layer (IPL) and an n-type layer (NL), wherein the APL has a larger band gap than the IPL and wherein excitons generated by optical absorption in the APL may be transferred to the IPL, resulting in the creation of additional excitons in this layer.
Data Source
AI summary
The disclosure relates to organic photovoltaic cells comprising a heterojunction structure formed by a first organic donor layer and a first organic acceptor layer, and further comprising a second organic acceptor layer adjacent to the first organic acceptor layer and/or a second organic donor layer adjacent to the first organic donor layer. The materials of the first acceptor layer and the second acceptor layer are selected to allow exciton dissociation by charge transfer at their interface, and to simultaneously allow exciton energy transfer at their interface. The materials of the first donor layer and the second donor layer are selected to allow exciton dissociation by charge transfer at their interface, and to simultaneously allow exciton energy transfer at their interface. Organic photovoltaic cells of the present invention may have a high short-circuit current density, a good open-circuit voltage and a good fill factor.