High-efficiency single and tandem fullerene solar cells with asymmetric monofluorinated diketopyrrolopyrrole-based polymer

Design and synthesis of low bandgap(LBG) polymer donors is inevitably challenging and their processability from a non-halogenated solvent system remains a hurdle to overcome in the area of highperformance polymer solar cells(PSCs).Due to a high aggregation tendency of LBG polymers,especially diketopyrrolopyrrole(DPP)-based polymers coupled with bithiophenes in the polymer backbones,their widespread adoption in non-ha logena ted solvent-processed PSCs has been limited.Herein,a novel LBG DPP-based polymer,called PDPP4 T-1 F with asymmetric arrangement of fluorine atom,has been successfully synthesized and showed an outstanding power conversion efficiency(PCE) of 10.10% in a singlejunction fullerene-based PSCs.Furthermore,an impressive PCE of 13.21% has been achieved in a tandem device from a fully non-halogenated solvent system,which integrates a wide bandgap PDTBTBz-2 F polymer in the bottom cell and LBG PDPP4 T-1 F polymer in the top cell.The achieved efficiency is the highest value reported in the literature to date in fullerene-based tandem PSCs.We found that a uniformly distributed interpenetrating fibril network with nano-scale phase separation and anisotropy of the polymer backbone orientation for efficient charge transfer/transport and suppressed charge recombination in PDPP4 T-1 F-based PSCs led to outstanding PCEs in single and tandem-junction PSCs.

Path to the fabrication of efficient, stable and commercially viable large-area organic solar cells

Organic solar cells(OSCs)have reached an outstanding certified power conversion efficiency(PCE)of over 19%in single junction and 20%in tandem architecture design.Such high PCEs have emerged with outstanding Y-shaped Y6 non-fullerene acceptors(NFAs),together with PM6 electron donor polymers.PCEs are on the rise for small-area OSCs.However,large-area OSC sub-modules are still unable to achieve such high PCEs,and the highest certified PCE reported so far is∼12%having an area of 58 cm2.To fabricate efficient large-area OSCs,new custom-designed NFAs for large-area systems are imminent along with improvements in the sub-module fabrication platforms.Moreover,the search for stable yet efficient OSCs is still in progress.In this review,progress in small-area OSCs is presented with reference to the advancement in the chemical structure of NFAs and donor polymers.Finally,the life-cycle assessment of OSCs is presented and the energy payback time of the efficient and stable OSCs is discussed and lastly,an outlook for the OSCs is given.