Inverted Semitransparent OPV Cells with ZnO Buffer
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Solution Overview
Problem
Semitransparent organic photovoltaic (OPV) cells have relatively low power conversion efficiency due to their reliance on bilayer or mixed heterojunction structures, which limit their application in building-integrated photovoltaics and require the use of optically lossy metal layers.
Innovation Solution
Inverted semitransparent OPV cells with mixed and hybrid planar-mixed heterojunctions using transparent indium tin oxide contacts and a hole blocking/electron selective sol-gel ZnO layer, eliminating thin metal layers and enabling efficient electron collection, along with MoO3 as a buffer for charge carrier extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If bilayer or mixed heterojunction structures are used in semitransparent OPV cells, then the device structure is simplified, but the power conversion efficiency remains relatively low
Solution Approach 1:
The device is segmented into distinct functional layers: a planar heterojunction layer for efficient charge separation and a mixed heterojunction layer for enhanced light absorption. This segmentation allows each layer to optimize its function, resolving the contradiction between structural simplicity and energy conversion efficiency.
Solution Approach 2:
The patent employs a composite heterojunction structure combining planar and mixed heterojunction layers with different material compositions. The planar layer uses donor-acceptor blends for charge separation, while the mixed layer incorporates additional materials for broadband absorption, achieving high efficiency without excessive complexity.
2Reliability
If metal layers are used in conventional OPV structures, then charge carrier extraction is achieved, but optical loss increases due to the optically lossy nature of metal layers
Solution Approach 1:
The patent extracts and removes the optically lossy metal layers from the device structure. Instead, transparent conducting oxides are used as electrode materials, eliminating the source of optical absorption while maintaining electrical functionality for charge carrier extraction.
Solution Approach 2:
The optical properties of the electrode materials are changed by transitioning from metallic materials with high optical absorption to transparent conducting oxide materials with high transparency. This parameter change in material composition eliminates optical loss while preserving electrical conductivity for charge extraction.
3Reliability
If wide energy gap molecules are used as cathode buffers, then the cathode buffer function is achieved, but symmetric ITO contacts cannot be employed due to lack of electron-transporting defect states
Solution Approach 1:
The patent copies the successful cathode buffer design from conventional structures and applies it symmetrically to both electrodes. By using the same wide energy gap molecule as buffer at both cathode and anode interfaces, the device achieves symmetric ITO contacts while maintaining reliable charge carrier extraction at both electrodes.
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 inverted PM-HJ architecture achieves >10% higher power conversion efficiency compared to mixed HJ cells and optimal tandem cells reach PCE=5.3% with balanced transparency and efficiency, while single junction cells can be tailored for specific applications.
Implementation Method 1
The ZnO has a high electron mobility of ∼10 cm2/V·s
Implementation Method 2
inverted semitransparent photovoltaic cells
Data Source
AI summary
Semitransparent organic photovoltaic (OPV) cells provide integrated photovoltaic needs, such as use on windows and other architectural surfaces. These cells can achieve high power conversion efficiency and supply acceptable transparency. Inverted, semitransparent OPV cells are provided that include a mixed organic heterojunction layer or a planar-mixed heterojunction layer. These cells can additionally be used to create a tandem cell, which absorbs light over a broader range of wavelengths.