High Performance All-Polymer Solar Cells by Synergistic Effects of Fine-Tuned Crystallinity and Solvent Annealing

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Polymer acceptors are emerging as alternatives to fullerene derivatives in high-performance all-polymer solar cells (all-PSCs).
• Low fill factor (FF), often below 0.65, is a significant limitation in all-PSC efficiency, linked to poor charge mobility and film morphology in polymer:polymer blends.

Purpose of the Study:

• To develop a facile method for modulating the crystallinity of naphthalene diimide (NDI)-based polymer acceptors.
• To enhance the performance of all-polymer solar cells (all-PSCs) by optimizing polymer blend morphology and charge transport properties.

Main Methods:

• Synthesized a series of random polymers (PNDI-Tx) by replacing bithiophene (2T) units with single thiophene (T) units in the N2200 backbone.
• Investigated the miscibility and nanostructure of PNDI-T10 with the donor polymer PTB7-Th.
• Employed solvent annealing (SA) to improve film morphology, charge mobility, and reduce recombination.

Main Results:

• The PNDI-T10 acceptor showed good miscibility with PTB7-Th, leading to a nanostructured blend that facilitated exciton dissociation and charge transport.
• Solvent annealing significantly increased hole and electron mobilities and suppressed bimolecular recombination.
• PTB7-Th:PNDI-T10 solar cells achieved a power conversion efficiency (PCE) of 7.6% and a fill factor (FF) of 0.71, a significant improvement over PTB7-Th:N2200 cells.

Conclusions:

• Rational design of polymer acceptors with fine-tuned crystallinity is crucial for high-performance all-PSCs.
• Optimized structure and morphology engineering of semicrystalline polymer:polymer blends show high potential for advancing all-PSC technology.
• Achieved record fill factor (FF) of 0.71 highlights the effectiveness of the developed strategy.