Conjugated Polymers for OPV via Solubilizing Groups
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Solution Overview
Problem
Current organic semiconducting materials face challenges such as insolubility, high toxicity in production, low charge carrier mobility, and instability, which hinder their use in mass-produced organic photovoltaic devices with high efficiency and stability.
Innovation Solution
Development of conjugated semiconducting polymers based on 4,8-benzo[1,2-b;4,5-b']dithiophene units with additional solubilizing groups, allowing for easy synthesis and high charge carrier mobility through aryl-aryl coupling reactions, avoiding toxic reagents and side reactions like deboronation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If poly(isothianaphthene) is prepared chemically or electrochemically to achieve quinoidal structure, then the bandgap is reduced and light absorption is improved, but the polymer becomes insoluble due to lack of solubilizing functionality
Solution Approach 1:
The patent applies local quality by introducing solubilizing groups (alkyl chains, alkoxy groups, or silyl groups) at specific positions (2- and 6-positions) of the BDT unit, while maintaining the quinoidal core structure intact for light absorption. This localized modification resolves the contradiction by adding solubility functionality without compromising the electronic properties needed for light harvesting.
Solution Approach 2:
The patent creates composite structures by combining the BDT core unit with various solubilizing side groups (alkyl, alkoxy, silyl) to form hybrid polymer structures. These composite materials integrate both the light-absorbing quinoidal core and the solubility-enhancing side chains, simultaneously achieving both improved light absorption and solubility for solution processing.
2Productivity
If Suzuki coupling is used to prepare polymers from thiophene-containing monomers, then the polymerization can proceed, but deboronation side-reactions occur to a significant degree leading to low molecular weight polymer chains
Solution Approach 1:
The patent extracts the problematic boronic acid/boronic acid ester groups from the thiophene rings and relocates the coupling functionality to the 4- and 8-positions of the BDT unit. This removal of the deboronation-prone groups from the reaction site eliminates the side reaction while maintaining polymerization capability through alternative coupling methods at the stabilized BDT positions.
Solution Approach 2:
The BDT unit acts as an intermediary structure that stabilizes the coupling reaction. By positioning the reactive groups at the 4- and 8-positions of the BDT unit rather than directly on the thiophene rings, the patent introduces a stabilizing intermediary framework that prevents deboronation while still enabling efficient aryl-aryl coupling to form high molecular weight polymers.
3Productivity
If Stille coupling is used to prepare polymers like poly(thieno[3,4-b]thiophene-benzo[1,2-b:4,5-b']dithiophene), then the polymerization proceeds successfully, but highly toxic organotin reagents must be used which is undesirable for mass production
Solution Approach 1:
The patent changes the chemical parameters of the coupling reaction by replacing toxic organotin reagents with less harmful alternatives. By modifying the monomer structure to enable coupling at the BDT 4- and 8-positions, the patent allows the use of safer reagents while maintaining successful polymerization, thereby eliminating toxicity concerns for mass production.
Solution Approach 2:
The patent adopts a more sustainable approach by replacing expensive and toxic organotin reagents with cheaper and environmentally friendlier coupling reagents. This substitution aligns with green chemistry principles, making the polymerization process more suitable for large-scale manufacturing by eliminating hazardous waste disposal requirements.
4Ease of manufacture
If alkyl groups are added to poly(isothianaphthene) to improve solubility, then solubility increases, but the semiconducting properties and suitability for OPV devices are not established
Solution Approach 1:
The patent segments the polymer structure into distinct functional domains: the BDT core unit maintains semiconducting properties for OPV applications, while separate solubilizing side groups (alkyl, alkoxy, or silyl groups) provide solubility. This segmentation allows each part to fulfill its specific function without compromising the other, ensuring both processability and electronic performance.
Solution Approach 2:
Instead of adding solubilizing groups to a pre-formed semiconducting backbone (which may compromise electronic properties), the patent inverts the approach by designing the BDT core unit first with inherent semiconducting properties, then systematically adding solubilizing groups at positions that do not interfere with charge transport. This inversion ensures semiconducting reliability is preserved while achieving solubility.
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 polymers exhibit high solubility, low bandgap, and oxidative stability, making them suitable for organic electronic devices, particularly in bulk heterojunction organic photovoltaic cells with improved light harvesting and efficiency.
Implementation Method 1
an extension of the effective conjugation length. It is generally observed in conjugated polymers that an increase in the conjugation length results in a decrease of the bandgap, leading to a higher degree of absorbed incident light
Data Source
Figure 1~2
AI summary
The invention relates to novel polymers containg repeating units based on benzodithiophene or derivatives thereof, monomers and methods for their preparation, their use as semiconductors in organic electronic (OE) devices, especially in organic photovoltaic (OPV) devices, and to OE and OPV devices comprising these polymers.