Sequential deposition: optimization of solvent swelling for high-performance polymer solar cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Organic solar cells (OSCs) offer a promising alternative to conventional photovoltaics due to their flexibility and low-cost fabrication.
• Achieving optimal morphology in the bulk heterojunction (BHJ) active layer is crucial for efficient charge generation and transport in OSCs.
• Sequential deposition methods are attractive for OSC fabrication but often require thermal annealing to optimize morphology.

Purpose of the Study:

• To investigate the impact of solvent swelling on the morphology and performance of organic solar cells fabricated via sequential deposition.
• To explore solvent swelling as an alternative to thermal annealing for optimizing BHJ morphology in DPP-based OSCs.
• To achieve high power conversion efficiency (PCE) in OSCs using a simplified sequential processing method.

Main Methods:

• Systematic optimization of organic solar cells using a DPP polymer via a solvent swelling assisted sequential deposition process.
• Morphological and structural characterization of the active layer films.
• Device performance testing to evaluate power conversion efficiency (PCE), open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF).

Main Results:

• Solvent swelling successfully induced ideal bulk heterojunction morphology, leading to improved device performance.
• A distinct trilayered morphology was observed, with preferential segregation of donor and acceptor materials.
• The optimized sequential deposition strategy, by tuning PC71BM solution concentration, yielded a high PCE of 7.59% without thermal annealing.

Conclusions:

• Solvent swelling is an effective strategy for controlling morphology and enhancing performance in sequentially deposited organic solar cells.
• This approach offers a simplified and efficient alternative to thermal annealing for fabricating high-performance DPP-based OSCs.
• The achieved 7.59% PCE represents a significant advancement for sequential processing methods in organic photovoltaics.