Conjugated Polymers for High Fill Factor Solar Cells
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Solution Overview
Problem
Bulk-heterojunction polymer solar cells face limitations in achieving high fill factors due to constraints in carrier mobility, film morphology, and interfacial charge recombination, which hinder their power conversion efficiency despite advancements in short-circuit current and open-circuit voltage.
Innovation Solution
Development of novel polymeric compounds with optimized optical absorption, charge transport characteristics, and chemical stability, incorporating bithiopheneimide and terthiophene units, which enhance fill factor and power conversion efficiency by promoting crystallinity and interfacial interactions in solar cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly crystalline polymers are used to enhance carrier mobility and fill factor, then charge transport is improved, but aggregation, solubility, and phase separation deteriorate
Solution Approach 1:
The patent modifies the polymer structure by introducing specific side chains and controlling molecular weight to achieve optimal crystallinity without excessive aggregation. This parameter optimization allows the material to maintain high carrier mobility while preserving good solubility and controlled phase separation in PCBM blends.
Solution Approach 2:
The patent creates composite systems by blending the polymer with PCBM (phenyl-C61-butyric acid methyl ester) in controlled ratios. This composite approach allows the crystalline polymer domains to provide high carrier mobility while the PCBM matrix maintains solubility and prevents excessive aggregation, achieving synergistic performance.
2Quantity of substance
If narrow bandgap polymers are developed to maximize solar photon capture and increase Jsc, then short-circuit current is improved, but fill factor and power conversion efficiency remain constrained
Solution Approach 1:
The patent introduces specific functional groups and side chain modifications at localized positions within the polymer structure. These local structural optimizations enhance charge transport properties and crystallinity in specific regions, allowing the material to maintain narrow bandgap for high photon capture while achieving improved fill factor through enhanced local order and mobility.
3Reliability
If polymers are optimized for high open-circuit voltage by lowering HOMO level, then Voc and environmental stability are improved, but fill factor remains below 70%
Solution Approach 1:
The patent divides the polymer structure into distinct functional segments: a core unit responsible for high Voc through low HOMO level, and side chain segments optimized for crystallinity and charge transport. This segmentation allows independent optimization of each function, achieving both high environmental stability and improved fill factor above 70%.
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 novel polymeric compounds demonstrate high fill factors and power conversion efficiencies, exceeding 7% in some cases, by optimizing the microstructure and charge transport in polymer solar cells, leading to improved solar energy harvesting performance.
Implementation Method 1
Bulk-heterojunction (BHJ) polymer solar cells (PSCs) based on interpenetrating polymer donor and fullerene acceptor networks offer a compelling approach to efficient solar energy harvesting
Implementation Method 2
Mobilities in turn are sensitive to the film morphology, with order typically enhancing transport. However, highly crystalline polymers can also exhibit deleterious aggregation
Data Source
AI summary
The present invention relates to certain polymeric compounds and their use as organic semiconductors in organic and hybrid optical, optoelectronic, and/or electronic devices such as photovoltaic cells, light emitting diodes, light emitting transistors, and field effect transistors. The present compounds can provide improved device performance, for example, as measured by power conversion efficiency, fill factor, open circuit voltage, field-effect mobility, on/off current ratios, and/or air stability when used in photovoltaic cells or transistors. The present compounds can have good solubility in common solvents enabling device fabrication via solution processes.