Side chain engineering in DTBDT-based small molecules for efficient organic photovoltaics

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Small-molecule organic photovoltaics (OPVs) offer potential for low-cost, flexible solar energy conversion.
• Achieving optimal morphology and charge transport in small-molecule/fullerene blends remains a key challenge.
• Dithieno[2,3-d:2',3'-d']-benzo[1,2-b:4,5-b']-dithiophene (DTBDT) core-based materials are promising for OPVs.

Purpose of the Study:

• To design and synthesize a new DTBDT-based small-molecule donor with improved miscibility and intermolecular interactions.
• To investigate the effect of alkyl and alkylthio substituents on blend morphology and photovoltaic performance.
• To enhance the performance of DTBDT-based OPVs through solvent vapor annealing (SVA) treatment.

Main Methods:

• Synthesis of a novel small-molecule donor, DTBDT-S-C8-TTR, featuring DTBDT core with alkyl and alkylthio substituents.
• Fabrication of bulk heterojunction solar cells using DTBDT-S-C8-TTR and PC71BM.
• Characterization of blend morphology using techniques sensitive to molecular ordering and aggregation.
• Optimization of film morphology via solvent vapor annealing (SVA) treatment.

Main Results:

• The synthesized DTBDT-S-C8-TTR exhibits good miscibility with PC71BM, forming homogenous blends with small domains and edge-on crystalline structures.
• The initial blend achieved a maximum power conversion efficiency (PCE) of 8.43%.
• SVA treatment induced well-developed crystalline domains and interconnected fibrillar structures, significantly improving charge carrier transport.
• The SVA-treated devices reached a maximum PCE of 9.18%.

Conclusions:

• The strategic incorporation of both alkylthio and alkyl groups onto the DTBDT core effectively enhances miscibility and intermolecular interactions in small-molecule OPVs.
• Solvent vapor annealing is a viable strategy to recover and improve the crystallinity of small-molecule/fullerene blends, leading to superior photovoltaic performance.
• DTBDT-based small molecules with tailored substituents show significant promise for high-performance organic photovoltaic applications.