A research team from Osaka Metropolitan University has developed a donor-acceptor-donor molecule that can spontaneously self-assemble into nanoscale structures, providing a more stable route to built-in p/n heterojunctions in organic solar cells.
Scientists from Osaka Metropolitan University have developed a molecular architecture that provides a new design strategy for the production of more efficient organic thin-film solar cells.
Their donor-acceptor-donor (DAD) molecule, known as TISQ, integrates a squaraine-based p-type segment and a naphthalene diimide n-type segment within a single molecule. It is able to naturally form p/n junctions, also known as the interface between p-type and n-type semiconductors.
The two segments are linked via amide groups that promote hydrogen bonding, meaning TISQ can spontaneously self-assemble into various nanoscale structures, which the scientists say could provide a more stable route to built-in p/n heterojunctions.
Takeshi Maeda, associate professor at the university’s Graduate School of Engineering and lead author of the study, explained that depending on the solvent, TISQ can spontaneously organize into nanoparticle-like J-type or nanofibrous H-type aggregates.
The university’s press release explains that polar solvents cause TISQ to form nanoparticle-like J-type aggregates via a cooperative nucleation-extension process, while low-polarity solvents cause it to assemble into fibrous H-type aggregates via an isodesmic mechanism. “Both exhibit different electronic behavior, especially in how efficiently they transport charges when light hits them,” Maeda said.
The team’s research fabricated organic thin-film solar cells incorporating TISQ as a single-component photoactive material in a test of the device’s applicability. The molecule was shown to form nanoscale p/n heterojunctions through self-assembly, which the scientists say highlights the feasibility of molecular designs that autonomously organize into functional electronic structures.
Because the energy conversion efficiency of the fabricated cells remains low, the team recognized that further research is needed before putting it into practice. Nevertheless, they concluded that their findings demonstrate how differences in nanoscale self-assembled p/n heterojunction structures directly influence the photocurrent response in a single-component system.
“Our focus is on developing molecular design strategies that use self-assembly to connect nanoscale p/n heterojunction structures with photoelectronic responses in single-component organic systems,” said Maeda. “By deepening this understanding of structure and function, we aim to broaden the design space of organic thin-film solar cells and related optoelectronic materials.”
The new molecule is described in the research article “Solvent-controlled supramolecular polymerization and morphology-dependent photoconductivity modulation in a squaraine-naphthalene diimide-squaraine bulk p/n heterojunction”, available in the magazine Angewandte Chemie International Edition.
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