Reinforcing Bulk Heterojunction Morphology through Side Chain-Engineered Pyrrolopyrrole-1,3-dione Polymeric Donors for Nonfullerene Organic Solar Cells

Abstract

Organic solar cells (OSCs) are attracting significant attention due to their low cost, lightweight, and flexible nature. The introduction of non-fullerene acceptors (NFAs) has propelled OSC development into a transformative era. However, the limited availability of wide bandgap polymer donors for NFAs poses a critical challenge, hindering further advancements. This study examines the role of developed wide bandgap halogenated pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD)- based polymers, in combination with the Y6 non-fullerene acceptor, in bulk heterojunction (BHJ) OSCs. We first focus on the electronic and absorbance modifications brought about by halogen substitution in PPD-based polymers, revealing how these adjustments influence the HOMO/LUMO energy levels and, subsequently, photovoltaic performance. Despite the increased Voc of halogenated polymers due to the optimal band alignment, power conversion efficiencies (PCE) were decreased due to suboptimal blend morphologies. We secondly implemented PPD as a solid additive to PM6:Y6, forming ternary OSCs and further improving the PCE. The study provides a nuanced understanding of the interplay between molecular design, device morphology and OSC performance, and opens insights for future research to achieve an optimal balance between band alignment and favorable blend morphology for high-efficiency OSCs.