Scientists at Osaka Metropolitan University have developed a new molecule, TISQ, capable of naturally forming p/n junctions. These junctions are essential for converting sunlight into electricity, and this discovery offers a new method for producing more efficient organic thin-film solar cells. This research focuses on overcoming challenges in creating optimal interfaces between p-type and n-type semiconductor materials in organic solar cells.
Organic thin-film solar cells are lightweight, flexible, and cost-effective alternatives to traditional silicon cells, with potential applications in printable electronics. However, their efficiency has lagged. Traditionally, p/n interfaces are formed by physically mixing p-type and n-type molecules, which can lead to inconsistencies and reduced performance due to processing variations.
The Osaka team explored an alternative strategy where p-type and n-type semiconductor components are integrated within a single molecule. They designed TISQ, a donor–acceptor–donor molecule that includes a squaraine-based p-type segment (donor) and a naphthalene diimide n-type segment (acceptor). These segments are linked by amide groups, which facilitate hydrogen bonding and enable TISQ to spontaneously self-assemble into distinct nanoscale structures.
Their research revealed that TISQ forms either J-type or H-type aggregates depending on the solvent used. J-type aggregates, formed in polar solvents through a cooperative nucleation–elongation process, exhibited nearly double the photocurrent response compared to H-type aggregates, which assembled in low-polarity solvents via an isodesmic mechanism.
To test the practical application, the team fabricated organic thin-film solar cells using TISQ as a single-component photoactive material. The molecule successfully formed nanoscale p/n heterojunctions through self-assembly, demonstrating the viability of designing molecules that autonomously organize into functional electronic structures.
While the power conversion efficiency of these initial cells is currently low and requires further development for practical use, the study highlights how variations in self-assembled nanoscale p/n heterojunction structures directly impact the photocurrent response within a single-component system. The researchers aim to deepen the understanding of this structure–function relationship to expand the design possibilities for organic thin-film solar cells and related optoelectronic materials.